From 134e34c6fefc644279780b812e0cb1b6fc6acea7 Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Mon, 14 Dec 2020 21:07:37 -0800
Subject: [PATCH 1/7] Implemente LRO Operation Callable Method sample code

---
 .../composer/ServiceClientClassComposer.java  | 44 +++++++--
 .../ServiceClientCommentComposer.java         |  7 +-
 .../ServiceClientSampleCodeComposer.java      | 96 ++++++++++++++++++
 .../gapic/composer/goldens/EchoClient.golden  | 14 ++-
 .../goldens/asset/AssetServiceClient.java     | 16 +++
 .../goldens/redis/CloudRedisClient.java       | 97 +++++++++++++++++++
 6 files changed, 264 insertions(+), 10 deletions(-)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
index ccd8cafaf2..e9ec95a840 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
@@ -500,7 +500,8 @@ private static List<MethodDefinition> createServiceMethods(
                 resourceNames));
       }
       if (method.hasLro()) {
-        javaMethods.add(createLroCallableMethod(service, method, types));
+        javaMethods.add(
+            createLroCallableMethod(service, method, types, messageTypes, resourceNames));
       }
       if (method.isPaged()) {
         javaMethods.add(createPagedCallableMethod(service, method, types));
@@ -680,25 +681,44 @@ private static MethodDefinition createMethodDefaultMethod(
   }
 
   private static MethodDefinition createLroCallableMethod(
-      Service service, Method method, Map<String, TypeNode> types) {
-    return createCallableMethod(service, method, types, CallableMethodKind.LRO);
+      Service service,
+      Method method,
+      Map<String, TypeNode> types,
+      Map<String, Message> messageTypes,
+      Map<String, ResourceName> resourceNames) {
+    return createCallableMethod(
+        service, method, CallableMethodKind.LRO, types, messageTypes, resourceNames);
   }
 
   private static MethodDefinition createCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
-    return createCallableMethod(service, method, types, CallableMethodKind.REGULAR);
+    return createCallableMethod(
+        service,
+        method,
+        CallableMethodKind.REGULAR,
+        types,
+        Collections.emptyMap(),
+        Collections.emptyMap());
   }
 
   private static MethodDefinition createPagedCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
-    return createCallableMethod(service, method, types, CallableMethodKind.PAGED);
+    return createCallableMethod(
+        service,
+        method,
+        CallableMethodKind.PAGED,
+        types,
+        Collections.emptyMap(),
+        Collections.emptyMap());
   }
 
   private static MethodDefinition createCallableMethod(
       Service service,
       Method method,
+      CallableMethodKind callableMethodKind,
       Map<String, TypeNode> types,
-      CallableMethodKind callableMethodKind) {
+      Map<String, Message> messageTypes,
+      Map<String, ResourceName> resourceNames) {
     TypeNode rawCallableReturnType = null;
     if (callableMethodKind.equals(CallableMethodKind.LRO)) {
       rawCallableReturnType = types.get("OperationCallable");
@@ -740,9 +760,19 @@ private static MethodDefinition createCallableMethod(
             .setReturnType(returnType)
             .build();
 
+    Optional<String> sampleCode = Optional.empty();
+    // TODO (summerji): Implement sample code for CallableMethodKind.PAGED and
+    // CallableMethodKind.REGULAR
+    if (callableMethodKind.equals(CallableMethodKind.LRO)) {
+      sampleCode =
+          Optional.of(
+              ServiceClientSampleCodeComposer.composeRpcLroCallableMethodHeaderSampleCode(
+                  method, types.get(getClientClassName(service)), resourceNames, messageTypes));
+    }
+
     return MethodDefinition.builder()
         .setHeaderCommentStatements(
-            ServiceClientCommentComposer.createRpcCallableMethodHeaderComment(method))
+            ServiceClientCommentComposer.createRpcCallableMethodHeaderComment(method, sampleCode))
         .setScope(ScopeNode.PUBLIC)
         .setIsFinal(true)
         .setName(methodName)
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientCommentComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientCommentComposer.java
index c3b9158d9b..c5ee9a98d6 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientCommentComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientCommentComposer.java
@@ -215,7 +215,8 @@ static CommentStatement createMethodSettingsArgComment(String serviceName) {
     return toSimpleComment(String.format(CREATE_METHOD_SETTINGS_ARG_PATTERN, serviceName));
   }
 
-  static List<CommentStatement> createRpcCallableMethodHeaderComment(Method method) {
+  static List<CommentStatement> createRpcCallableMethodHeaderComment(
+      Method method, Optional<String> sampleCode) {
     JavaDocComment.Builder methodJavadocBuilder = JavaDocComment.builder();
 
     if (method.hasDescription()) {
@@ -224,7 +225,9 @@ static List<CommentStatement> createRpcCallableMethodHeaderComment(Method method
     }
 
     methodJavadocBuilder.addParagraph(METHOD_DESCRIPTION_SAMPLE_CODE_SUMMARY_STRING);
-    // TODO(summerji): Add sample code here.
+    if (sampleCode.isPresent()) {
+      methodJavadocBuilder.addSampleCode(sampleCode.get());
+    }
 
     return Arrays.asList(
         CommentComposer.AUTO_GENERATED_METHOD_COMMENT,
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
index b60c329ab5..6d59f71051 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
@@ -15,6 +15,7 @@
 package com.google.api.generator.gapic.composer;
 
 import com.google.api.gax.core.FixedCredentialsProvider;
+import com.google.api.gax.longrunning.OperationFuture;
 import com.google.api.generator.engine.ast.AssignmentExpr;
 import com.google.api.generator.engine.ast.CommentStatement;
 import com.google.api.generator.engine.ast.ConcreteReference;
@@ -289,6 +290,101 @@ public static String composeRpcDefaultMethodHeaderSampleCode(
             .build());
   }
 
+  public static String composeRpcLroCallableMethodHeaderSampleCode(
+      Method method,
+      TypeNode clientType,
+      Map<String, ResourceName> resourceNames,
+      Map<String, Message> messageTypes) {
+    VariableExpr clientVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder()
+                .setName(JavaStyle.toLowerCamelCase(clientType.reference().name()))
+                .setType(clientType)
+                .build());
+    // Assign method's request variable with the default value.
+    VariableExpr requestVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder().setName("request").setType(method.inputType()).build());
+    Message requestMessage = messageTypes.get(method.inputType().reference().simpleName());
+    Preconditions.checkNotNull(requestMessage);
+    Expr requestBuilderExpr =
+        DefaultValueComposer.createSimpleMessageBuilderExpr(
+            requestMessage, resourceNames, messageTypes);
+    List<Expr> bodyExprs = new ArrayList<>();
+    bodyExprs.add(
+        AssignmentExpr.builder()
+            .setVariableExpr(requestVarExpr.toBuilder().setIsDecl(true).build())
+            .setValueExpr(requestBuilderExpr)
+            .build());
+    TypeNode operationFutureType =
+        TypeNode.withReference(
+            ConcreteReference.builder()
+                .setClazz(OperationFuture.class)
+                .setGenerics(
+                    method.lro().responseType().reference(),
+                    method.lro().metadataType().reference())
+                .build());
+    VariableExpr operationFutureVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder().setName("future").setType(operationFutureType).build());
+    MethodInvocationExpr rpcMethodInvocationExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(clientVarExpr)
+            .setMethodName(
+                String.format("%sOperationCallable", JavaStyle.toLowerCamelCase(method.name())))
+            .build();
+    rpcMethodInvocationExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(rpcMethodInvocationExpr)
+            .setMethodName("futureCall")
+            .setArguments(requestVarExpr)
+            .setReturnType(operationFutureType)
+            .build();
+    bodyExprs.add(
+        AssignmentExpr.builder()
+            .setVariableExpr(operationFutureVarExpr.toBuilder().setIsDecl(true).build())
+            .setValueExpr(rpcMethodInvocationExpr)
+            .build());
+    List<Statement> bodyStatements =
+        bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList());
+    bodyExprs.clear();
+    bodyStatements.add(CommentStatement.withComment(LineComment.withComment("Do something;")));
+    MethodInvocationExpr futureGetMethodExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(operationFutureVarExpr)
+            .setMethodName("get")
+            .setReturnType(method.lro().responseType())
+            .build();
+    boolean returnVoid = isProtoEmptyType(method.lro().responseType());
+    if (returnVoid) {
+      bodyExprs.add(futureGetMethodExpr);
+    } else {
+      VariableExpr responseVarExpr =
+          VariableExpr.builder()
+              .setVariable(
+                  Variable.builder()
+                      .setName("response")
+                      .setType(method.lro().responseType())
+                      .build())
+              .setIsDecl(true)
+              .build();
+      bodyExprs.add(
+          AssignmentExpr.builder()
+              .setVariableExpr(responseVarExpr)
+              .setValueExpr(futureGetMethodExpr)
+              .build());
+    }
+    bodyStatements.addAll(
+        bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList()));
+    bodyExprs.clear();
+    return SampleCodeWriter.write(
+        TryCatchStatement.builder()
+            .setTryResourceExpr(assignClientVariableWithCreateMethodExpr(clientVarExpr))
+            .setTryBody(bodyStatements)
+            .setIsSampleCode(true)
+            .build());
+  }
+
   private static List<Statement> composeUnaryRpcMethodSampleCodeBodyStatements(
       Method method,
       VariableExpr clientVarExpr,
diff --git a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
index 15d93be4eb..6e1e81732d 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
+++ b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
@@ -504,7 +504,19 @@ public class EchoClient implements BackgroundResource {
   }
 
   // AUTO-GENERATED DOCUMENTATION AND METHOD.
-  /** Sample code: */
+  /**
+   * Sample code:
+   *
+   * <pre>{@code
+   * try (EchoClient echoClient = EchoClient.create()) {
+   *   WaitRequest request = WaitRequest.newBuilder().build();
+   *   OperationFuture<WaitResponse, WaitMetadata> future =
+   *       echoClient.waitOperationCallable().futureCall(request);
+   *   // Do something;
+   *   WaitResponse response = future.get();
+   * }
+   * }</pre>
+   */
   public final OperationCallable<WaitRequest, WaitResponse, WaitMetadata> waitOperationCallable() {
     return stub.waitOperationCallable();
   }
diff --git a/test/integration/goldens/asset/AssetServiceClient.java b/test/integration/goldens/asset/AssetServiceClient.java
index 24702ea4f4..ecfe104374 100644
--- a/test/integration/goldens/asset/AssetServiceClient.java
+++ b/test/integration/goldens/asset/AssetServiceClient.java
@@ -202,6 +202,22 @@ public final OperationFuture<ExportAssetsResponse, ExportAssetsRequest> exportAs
    * export operation usually finishes within 5 minutes.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (AssetServiceClient assetServiceClient = AssetServiceClient.create()) {
+   *   ExportAssetsRequest request =
+   *       ExportAssetsRequest.newBuilder()
+   *           .setParent(FeedName.ofProjectFeedName("[PROJECT]", "[FEED]").toString())
+   *           .setReadTime(Timestamp.newBuilder().build())
+   *           .addAllAssetTypes(new ArrayList<String>())
+   *           .setOutputConfig(OutputConfig.newBuilder().build())
+   *           .build();
+   *   OperationFuture<ExportAssetsResponse, ExportAssetsRequest> future =
+   *       assetServiceClient.exportAssetsOperationCallable().futureCall(request);
+   *   // Do something;
+   *   ExportAssetsResponse response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<ExportAssetsRequest, ExportAssetsResponse, ExportAssetsRequest>
       exportAssetsOperationCallable() {
diff --git a/test/integration/goldens/redis/CloudRedisClient.java b/test/integration/goldens/redis/CloudRedisClient.java
index 72ebd6d532..40b756ba86 100644
--- a/test/integration/goldens/redis/CloudRedisClient.java
+++ b/test/integration/goldens/redis/CloudRedisClient.java
@@ -561,6 +561,21 @@ public final OperationFuture<Instance, OperationMetadata> createInstanceAsync(
    * call DeleteOperation.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   CreateInstanceRequest request =
+   *       CreateInstanceRequest.newBuilder()
+   *           .setParent(LocationName.of("[PROJECT]", "[LOCATION]").toString())
+   *           .setInstanceId("instanceId902024336")
+   *           .setInstance(Instance.newBuilder().build())
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.createInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<CreateInstanceRequest, Instance, OperationMetadata>
       createInstanceOperationCallable() {
@@ -658,6 +673,20 @@ public final OperationFuture<Instance, OperationMetadata> updateInstanceAsync(
    * DeleteOperation.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   UpdateInstanceRequest request =
+   *       UpdateInstanceRequest.newBuilder()
+   *           .setUpdateMask(FieldMask.newBuilder().build())
+   *           .setInstance(Instance.newBuilder().build())
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.updateInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<UpdateInstanceRequest, Instance, OperationMetadata>
       updateInstanceOperationCallable() {
@@ -765,6 +794,20 @@ public final OperationFuture<Instance, OperationMetadata> upgradeInstanceAsync(
    * Upgrades Redis instance to the newer Redis version specified in the request.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   UpgradeInstanceRequest request =
+   *       UpgradeInstanceRequest.newBuilder()
+   *           .setName(InstanceName.of("[PROJECT]", "[LOCATION]", "[INSTANCE]").toString())
+   *           .setRedisVersion("redisVersion-1972584739")
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.upgradeInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<UpgradeInstanceRequest, Instance, OperationMetadata>
       upgradeInstanceOperationCallable() {
@@ -856,6 +899,20 @@ public final OperationFuture<Instance, OperationMetadata> importInstanceAsync(
    * call DeleteOperation.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   ImportInstanceRequest request =
+   *       ImportInstanceRequest.newBuilder()
+   *           .setName("name3373707")
+   *           .setInputConfig(InputConfig.newBuilder().build())
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.importInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<ImportInstanceRequest, Instance, OperationMetadata>
       importInstanceOperationCallable() {
@@ -950,6 +1007,20 @@ public final OperationFuture<Instance, OperationMetadata> exportInstanceAsync(
    * call DeleteOperation.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   ExportInstanceRequest request =
+   *       ExportInstanceRequest.newBuilder()
+   *           .setName("name3373707")
+   *           .setOutputConfig(OutputConfig.newBuilder().build())
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.exportInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<ExportInstanceRequest, Instance, OperationMetadata>
       exportInstanceOperationCallable() {
@@ -1068,6 +1139,19 @@ public final OperationFuture<Instance, OperationMetadata> failoverInstanceAsync(
    * Cloud Memorystore for Redis instance.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   FailoverInstanceRequest request =
+   *       FailoverInstanceRequest.newBuilder()
+   *           .setName(InstanceName.of("[PROJECT]", "[LOCATION]", "[INSTANCE]").toString())
+   *           .build();
+   *   OperationFuture<Instance, OperationMetadata> future =
+   *       cloudRedisClient.failoverInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   Instance response = future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<FailoverInstanceRequest, Instance, OperationMetadata>
       failoverInstanceOperationCallable() {
@@ -1161,6 +1245,19 @@ public final OperationFuture<Empty, OperationMetadata> deleteInstanceAsync(
    * Deletes a specific Redis instance. Instance stops serving and data is deleted.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   DeleteInstanceRequest request =
+   *       DeleteInstanceRequest.newBuilder()
+   *           .setName(InstanceName.of("[PROJECT]", "[LOCATION]", "[INSTANCE]").toString())
+   *           .build();
+   *   OperationFuture<Empty, OperationMetadata> future =
+   *       cloudRedisClient.deleteInstanceOperationCallable().futureCall(request);
+   *   // Do something;
+   *   future.get();
+   * }
+   * }</pre>
    */
   public final OperationCallable<DeleteInstanceRequest, Empty, OperationMetadata>
       deleteInstanceOperationCallable() {

From fd01194021edea4e7781f68b9a5488b29752178b Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Tue, 15 Dec 2020 13:59:49 -0800
Subject: [PATCH 2/7] Add todo comment

---
 .../generator/gapic/composer/ServiceClientClassComposer.java    | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
index e9ec95a840..c6b3d19fc1 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
@@ -692,6 +692,7 @@ private static MethodDefinition createLroCallableMethod(
 
   private static MethodDefinition createCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
+    // TODO(summerji): Implement sample code for callable method and pass in actual map of Messages and ResourceNames
     return createCallableMethod(
         service,
         method,
@@ -703,6 +704,7 @@ private static MethodDefinition createCallableMethod(
 
   private static MethodDefinition createPagedCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
+    // TODO(summerji): Implement sample code for paged callable method and pass in actual map of Messages and ResourceNames
     return createCallableMethod(
         service,
         method,

From 3a73ee277ccf78d5f14e0833ceebb5013f019614 Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Thu, 17 Dec 2020 00:08:11 -0800
Subject: [PATCH 3/7] Add unit test

---
 .../composer/ServiceClientClassComposer.java  |  13 ++-
 .../ServiceClientSampleCodeComposer.java      |  11 +-
 .../ServiceClientSampleCodeComposerTest.java  | 108 ++++++++++++++++++
 3 files changed, 124 insertions(+), 8 deletions(-)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
index c6b3d19fc1..e90223575f 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
@@ -692,7 +692,8 @@ private static MethodDefinition createLroCallableMethod(
 
   private static MethodDefinition createCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
-    // TODO(summerji): Implement sample code for callable method and pass in actual map of Messages and ResourceNames
+    // TODO(summerji): Implement sample code for callable method and pass in actual map of Messages
+    // and ResourceNames
     return createCallableMethod(
         service,
         method,
@@ -704,7 +705,8 @@ private static MethodDefinition createCallableMethod(
 
   private static MethodDefinition createPagedCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
-    // TODO(summerji): Implement sample code for paged callable method and pass in actual map of Messages and ResourceNames
+    // TODO(summerji): Implement sample code for paged callable method and pass in actual map of
+    // Messages and ResourceNames
     return createCallableMethod(
         service,
         method,
@@ -768,8 +770,11 @@ private static MethodDefinition createCallableMethod(
     if (callableMethodKind.equals(CallableMethodKind.LRO)) {
       sampleCode =
           Optional.of(
-              ServiceClientSampleCodeComposer.composeRpcLroCallableMethodHeaderSampleCode(
-                  method, types.get(getClientClassName(service)), resourceNames, messageTypes));
+              ServiceClientSampleCodeComposer.composeLroCallableMethodHeaderSampleCode(
+                  method,
+                  types.get(ClassNames.getServiceClientClassName(service)),
+                  resourceNames,
+                  messageTypes));
     }
 
     return MethodDefinition.builder()
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
index 6d59f71051..b2fa6c9e02 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
@@ -290,7 +290,7 @@ public static String composeRpcDefaultMethodHeaderSampleCode(
             .build());
   }
 
-  public static String composeRpcLroCallableMethodHeaderSampleCode(
+  public static String composeLroCallableMethodHeaderSampleCode(
       Method method,
       TypeNode clientType,
       Map<String, ResourceName> resourceNames,
@@ -310,12 +310,15 @@ public static String composeRpcLroCallableMethodHeaderSampleCode(
     Expr requestBuilderExpr =
         DefaultValueComposer.createSimpleMessageBuilderExpr(
             requestMessage, resourceNames, messageTypes);
-    List<Expr> bodyExprs = new ArrayList<>();
-    bodyExprs.add(
+    AssignmentExpr requestAssignmentExpr =
         AssignmentExpr.builder()
             .setVariableExpr(requestVarExpr.toBuilder().setIsDecl(true).build())
             .setValueExpr(requestBuilderExpr)
-            .build());
+            .build();
+
+    List<Expr> bodyExprs = new ArrayList<>();
+    bodyExprs.add(requestAssignmentExpr);
+
     TypeNode operationFutureType =
         TypeNode.withReference(
             ConcreteReference.builder()
diff --git a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
index 3e5d82a8b0..b89c138163 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
+++ b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
@@ -1397,4 +1397,112 @@ public void validComposeRpcDefaultMethodHeaderSampleCode_pureUnaryReturnResponse
             "}");
     assertEquals(results, expected);
   }
+
+  // ================================LRO Callable Method Sample Code ====================//
+  @Test
+  public void validComposeLroCallableMethodHeaderSampleCode_withReturnResponse() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("WaitRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder().setName("Operation").setPakkage(LRO_PACKAGE_NAME).build());
+    TypeNode responseType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("WaitResponse")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode metadataType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("WaitMetadata")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    LongrunningOperation lro = LongrunningOperation.withTypes(responseType, metadataType);
+    Method method =
+        Method.builder()
+            .setName("Wait")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setLro(lro)
+            .build();
+    String results =
+        ServiceClientSampleCodeComposer.composeLroCallableMethodHeaderSampleCode(
+            method, clientType, resourceNames, messageTypes);
+    String expected =
+        LineFormatter.lines(
+            "try (EchoClient echoClient = EchoClient.create()) {\n",
+            "  WaitRequest request = WaitRequest.newBuilder().build();\n",
+            "  OperationFuture<WaitResponse, WaitMetadata> future =\n",
+            "      echoClient.waitOperationCallable().futureCall(request);\n",
+            "  // Do something;\n",
+            "  WaitResponse response = future.get();\n",
+            "}");
+    assertEquals(results, expected);
+  }
+
+  @Test
+  public void validComposeLroCallableMethodHeaderSampleCode_withReturnVoid() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("WaitRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder().setName("Operation").setPakkage(LRO_PACKAGE_NAME).build());
+    TypeNode responseType =
+        TypeNode.withReference(
+            VaporReference.builder().setName("Empty").setPakkage(PROTO_PACKAGE_NAME).build());
+    TypeNode metadataType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("WaitMetadata")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    LongrunningOperation lro = LongrunningOperation.withTypes(responseType, metadataType);
+    Method method =
+        Method.builder()
+            .setName("Wait")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setLro(lro)
+            .build();
+    String results =
+        ServiceClientSampleCodeComposer.composeLroCallableMethodHeaderSampleCode(
+            method, clientType, resourceNames, messageTypes);
+    String expected =
+        LineFormatter.lines(
+            "try (EchoClient echoClient = EchoClient.create()) {\n",
+            "  WaitRequest request = WaitRequest.newBuilder().build();\n",
+            "  OperationFuture<Empty, WaitMetadata> future =\n",
+            "      echoClient.waitOperationCallable().futureCall(request);\n",
+            "  // Do something;\n",
+            "  future.get();\n",
+            "}");
+    assertEquals(results, expected);
+  }
 }

From 6719f882b9272a7a9c92626d549d4af42bbb8733 Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Thu, 17 Dec 2020 00:27:15 -0800
Subject: [PATCH 4/7] add comments

---
 .../gapic/composer/ServiceClientClassComposer.java     |  5 +++--
 .../composer/ServiceClientSampleCodeComposer.java      | 10 ++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
index e90223575f..1634f121b7 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
@@ -692,8 +692,9 @@ private static MethodDefinition createLroCallableMethod(
 
   private static MethodDefinition createCallableMethod(
       Service service, Method method, Map<String, TypeNode> types) {
-    // TODO(summerji): Implement sample code for callable method and pass in actual map of Messages
-    // and ResourceNames
+    // TODO(summerji): Implement sample code for callable methods which include stream methods and
+    // unary methods,
+    //  and pass in actual map of Messages and ResourceNames
     return createCallableMethod(
         service,
         method,
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
index b2fa6c9e02..0c8acf717c 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
@@ -319,6 +319,9 @@ public static String composeLroCallableMethodHeaderSampleCode(
     List<Expr> bodyExprs = new ArrayList<>();
     bodyExprs.add(requestAssignmentExpr);
 
+    // Create OperationFuture variable expr with invoking client's lro callable method.
+    // e.g. OperationFuture<Empty, WaitMetadata> future =
+    //          echoClient.waitOperationCallable().futureCall(request);
     TypeNode operationFutureType =
         TypeNode.withReference(
             ConcreteReference.builder()
@@ -348,10 +351,16 @@ public static String composeLroCallableMethodHeaderSampleCode(
             .setVariableExpr(operationFutureVarExpr.toBuilder().setIsDecl(true).build())
             .setValueExpr(rpcMethodInvocationExpr)
             .build());
+
     List<Statement> bodyStatements =
         bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList());
     bodyExprs.clear();
+    // Add a line comment
     bodyStatements.add(CommentStatement.withComment(LineComment.withComment("Do something;")));
+
+    // Assign response variable with invoking client's lro method.
+    // e.g. if return void, future.get(); or,
+    // e.g. if return other type, WaitResponse response = future.get();
     MethodInvocationExpr futureGetMethodExpr =
         MethodInvocationExpr.builder()
             .setExprReferenceExpr(operationFutureVarExpr)
@@ -380,6 +389,7 @@ public static String composeLroCallableMethodHeaderSampleCode(
     bodyStatements.addAll(
         bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList()));
     bodyExprs.clear();
+
     return SampleCodeWriter.write(
         TryCatchStatement.builder()
             .setTryResourceExpr(assignClientVariableWithCreateMethodExpr(clientVarExpr))

From b7b7b2ee2d559dc89090f867e87c285b65b8d094 Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Thu, 17 Dec 2020 16:31:37 -0800
Subject: [PATCH 5/7] address the comments

---
 .../composer/ServiceClientSampleCodeComposer.java  |  8 ++++----
 .../ServiceClientSampleCodeComposerTest.java       |  4 ++--
 .../gapic/composer/goldens/EchoClient.golden       |  2 +-
 .../goldens/asset/AssetServiceClient.java          |  2 +-
 .../goldens/redis/CloudRedisClient.java            | 14 +++++++-------
 5 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
index 0c8acf717c..d26a1f129a 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
@@ -319,7 +319,7 @@ public static String composeLroCallableMethodHeaderSampleCode(
     List<Expr> bodyExprs = new ArrayList<>();
     bodyExprs.add(requestAssignmentExpr);
 
-    // Create OperationFuture variable expr with invoking client's lro callable method.
+    // Create OperationFuture variable expr with invoking client's LRO callable method.
     // e.g. OperationFuture<Empty, WaitMetadata> future =
     //          echoClient.waitOperationCallable().futureCall(request);
     TypeNode operationFutureType =
@@ -356,9 +356,9 @@ public static String composeLroCallableMethodHeaderSampleCode(
         bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList());
     bodyExprs.clear();
     // Add a line comment
-    bodyStatements.add(CommentStatement.withComment(LineComment.withComment("Do something;")));
+    bodyStatements.add(CommentStatement.withComment(LineComment.withComment("Do something.")));
 
-    // Assign response variable with invoking client's lro method.
+    // Assign response variable with invoking client's LRO method.
     // e.g. if return void, future.get(); or,
     // e.g. if return other type, WaitResponse response = future.get();
     MethodInvocationExpr futureGetMethodExpr =
@@ -494,7 +494,7 @@ private static List<Statement> composeUnaryLroRpcMethodSampleCodeBodyStatements(
       VariableExpr clientVarExpr,
       List<VariableExpr> rpcMethodArgVarExprs,
       List<Expr> bodyExprs) {
-    // Assign response variable with invoking client's lro method.
+    // Assign response variable with invoking client's LRO method.
     // e.g. if return void, echoClient.waitAsync(ttl).get(); or,
     // e.g. if return other type, WaitResponse response = echoClient.waitAsync(ttl).get();
     Expr invokeLroGetMethodExpr =
diff --git a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
index b89c138163..441bea4c65 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
+++ b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
@@ -1448,7 +1448,7 @@ public void validComposeLroCallableMethodHeaderSampleCode_withReturnResponse() {
             "  WaitRequest request = WaitRequest.newBuilder().build();\n",
             "  OperationFuture<WaitResponse, WaitMetadata> future =\n",
             "      echoClient.waitOperationCallable().futureCall(request);\n",
-            "  // Do something;\n",
+            "  // Do something.\n",
             "  WaitResponse response = future.get();\n",
             "}");
     assertEquals(results, expected);
@@ -1500,7 +1500,7 @@ public void validComposeLroCallableMethodHeaderSampleCode_withReturnVoid() {
             "  WaitRequest request = WaitRequest.newBuilder().build();\n",
             "  OperationFuture<Empty, WaitMetadata> future =\n",
             "      echoClient.waitOperationCallable().futureCall(request);\n",
-            "  // Do something;\n",
+            "  // Do something.\n",
             "  future.get();\n",
             "}");
     assertEquals(results, expected);
diff --git a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
index 6e1e81732d..b9585ec489 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
+++ b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
@@ -512,7 +512,7 @@ public class EchoClient implements BackgroundResource {
    *   WaitRequest request = WaitRequest.newBuilder().build();
    *   OperationFuture<WaitResponse, WaitMetadata> future =
    *       echoClient.waitOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   WaitResponse response = future.get();
    * }
    * }</pre>
diff --git a/test/integration/goldens/asset/AssetServiceClient.java b/test/integration/goldens/asset/AssetServiceClient.java
index ecfe104374..6a39beb127 100644
--- a/test/integration/goldens/asset/AssetServiceClient.java
+++ b/test/integration/goldens/asset/AssetServiceClient.java
@@ -214,7 +214,7 @@ public final OperationFuture<ExportAssetsResponse, ExportAssetsRequest> exportAs
    *           .build();
    *   OperationFuture<ExportAssetsResponse, ExportAssetsRequest> future =
    *       assetServiceClient.exportAssetsOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   ExportAssetsResponse response = future.get();
    * }
    * }</pre>
diff --git a/test/integration/goldens/redis/CloudRedisClient.java b/test/integration/goldens/redis/CloudRedisClient.java
index 40b756ba86..bf6aba5541 100644
--- a/test/integration/goldens/redis/CloudRedisClient.java
+++ b/test/integration/goldens/redis/CloudRedisClient.java
@@ -572,7 +572,7 @@ public final OperationFuture<Instance, OperationMetadata> createInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.createInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -683,7 +683,7 @@ public final OperationFuture<Instance, OperationMetadata> updateInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.updateInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -804,7 +804,7 @@ public final OperationFuture<Instance, OperationMetadata> upgradeInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.upgradeInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -909,7 +909,7 @@ public final OperationFuture<Instance, OperationMetadata> importInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.importInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -1017,7 +1017,7 @@ public final OperationFuture<Instance, OperationMetadata> exportInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.exportInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -1148,7 +1148,7 @@ public final OperationFuture<Instance, OperationMetadata> failoverInstanceAsync(
    *           .build();
    *   OperationFuture<Instance, OperationMetadata> future =
    *       cloudRedisClient.failoverInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   Instance response = future.get();
    * }
    * }</pre>
@@ -1254,7 +1254,7 @@ public final OperationFuture<Empty, OperationMetadata> deleteInstanceAsync(
    *           .build();
    *   OperationFuture<Empty, OperationMetadata> future =
    *       cloudRedisClient.deleteInstanceOperationCallable().futureCall(request);
-   *   // Do something;
+   *   // Do something.
    *   future.get();
    * }
    * }</pre>

From 4bc25482658c1cab75f55b8a74f9a4f1b09f4eeb Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Thu, 17 Dec 2020 12:26:01 -0800
Subject: [PATCH 6/7] Implement Paged Callable Method

---
 .../composer/ServiceClientClassComposer.java  |  27 ++--
 .../ServiceClientSampleCodeComposer.java      | 116 ++++++++++++++++++
 .../gapic/composer/goldens/EchoClient.golden  |  41 ++++++-
 .../composer/goldens/IdentityClient.golden    |  19 ++-
 .../goldens/asset/AssetServiceClient.java     |  38 ++++++
 .../goldens/library/LibraryServiceClient.java |  31 +++++
 .../goldens/logging/ConfigClient.java         |  52 ++++++++
 .../goldens/logging/LoggingClient.java        |  50 ++++++++
 .../goldens/logging/MetricsClient.java        |  16 +++
 .../goldens/redis/CloudRedisClient.java       |  17 +++
 10 files changed, 394 insertions(+), 13 deletions(-)

diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
index 1634f121b7..424e1d23c4 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientClassComposer.java
@@ -504,7 +504,8 @@ private static List<MethodDefinition> createServiceMethods(
             createLroCallableMethod(service, method, types, messageTypes, resourceNames));
       }
       if (method.isPaged()) {
-        javaMethods.add(createPagedCallableMethod(service, method, types));
+        javaMethods.add(
+            createPagedCallableMethod(service, method, types, messageTypes, resourceNames));
       }
       javaMethods.add(createCallableMethod(service, method, types));
     }
@@ -705,16 +706,13 @@ private static MethodDefinition createCallableMethod(
   }
 
   private static MethodDefinition createPagedCallableMethod(
-      Service service, Method method, Map<String, TypeNode> types) {
-    // TODO(summerji): Implement sample code for paged callable method and pass in actual map of
-    // Messages and ResourceNames
+      Service service,
+      Method method,
+      Map<String, TypeNode> types,
+      Map<String, Message> messageTypes,
+      Map<String, ResourceName> resourceNames) {
     return createCallableMethod(
-        service,
-        method,
-        CallableMethodKind.PAGED,
-        types,
-        Collections.emptyMap(),
-        Collections.emptyMap());
+        service, method, CallableMethodKind.PAGED, types, messageTypes, resourceNames);
   }
 
   private static MethodDefinition createCallableMethod(
@@ -777,6 +775,15 @@ private static MethodDefinition createCallableMethod(
                   resourceNames,
                   messageTypes));
     }
+    if (callableMethodKind.equals(CallableMethodKind.PAGED)) {
+      sampleCode =
+          Optional.of(
+              ServiceClientSampleCodeComposer.composePagedCallableMethodHeaderSampleCode(
+                  method,
+                  types.get(ClassNames.getServiceClientClassName(service)),
+                  resourceNames,
+                  messageTypes));
+    }
 
     return MethodDefinition.builder()
         .setHeaderCommentStatements(
diff --git a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
index d26a1f129a..59ecd59a4f 100644
--- a/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
+++ b/src/main/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposer.java
@@ -14,6 +14,7 @@
 
 package com.google.api.generator.gapic.composer;
 
+import com.google.api.core.ApiFuture;
 import com.google.api.gax.core.FixedCredentialsProvider;
 import com.google.api.gax.longrunning.OperationFuture;
 import com.google.api.generator.engine.ast.AssignmentExpr;
@@ -398,6 +399,121 @@ public static String composeLroCallableMethodHeaderSampleCode(
             .build());
   }
 
+  public static String composePagedCallableMethodHeaderSampleCode(
+      Method method,
+      TypeNode clientType,
+      Map<String, ResourceName> resourceNames,
+      Map<String, Message> messageTypes) {
+    VariableExpr clientVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder()
+                .setName(JavaStyle.toLowerCamelCase(clientType.reference().name()))
+                .setType(clientType)
+                .build());
+    // Assign method's request variable with the default value.
+    VariableExpr requestVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder().setName("request").setType(method.inputType()).build());
+    Message requestMessage = messageTypes.get(method.inputType().reference().simpleName());
+    Preconditions.checkNotNull(requestMessage);
+    Expr requestBuilderExpr =
+        DefaultValueComposer.createSimpleMessageBuilderExpr(
+            requestMessage, resourceNames, messageTypes);
+    AssignmentExpr requestAssignmentExpr =
+        AssignmentExpr.builder()
+            .setVariableExpr(requestVarExpr.toBuilder().setIsDecl(true).build())
+            .setValueExpr(requestBuilderExpr)
+            .build();
+
+    List<Expr> bodyExprs = new ArrayList<>();
+    bodyExprs.add(requestAssignmentExpr);
+
+    // Find the repeated field.
+    Message methodOutputMessage = messageTypes.get(method.outputType().reference().simpleName());
+    Field repeatedPagedResultsField = methodOutputMessage.findAndUnwrapFirstRepeatedField();
+    Preconditions.checkNotNull(
+        repeatedPagedResultsField,
+        String.format(
+            "No repeated field found on message %s for method %s",
+            methodOutputMessage.name(), method.name()));
+    TypeNode repeatedResponseType = repeatedPagedResultsField.type();
+
+    // Create ApiFuture Variable Expression with assign value by invoking client paged callable
+    // method.
+    // e.g. ApiFuture<ListExclusionsPagedResponse> future =
+    //          configServiceV2Client.listExclusionsPagedCallable().futureCall(request);
+    TypeNode apiFutureType =
+        TypeNode.withReference(
+            ConcreteReference.builder()
+                .setClazz(ApiFuture.class)
+                .setGenerics(repeatedResponseType.reference())
+                .build());
+    VariableExpr apiFutureVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder().setName("future").setType(apiFutureType).build());
+    MethodInvocationExpr pagedCallableFutureMethodExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(clientVarExpr)
+            .setMethodName(
+                String.format("%sPagedCallable", JavaStyle.toLowerCamelCase(method.name())))
+            .build();
+    pagedCallableFutureMethodExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(pagedCallableFutureMethodExpr)
+            .setMethodName("futureCall")
+            .setArguments(requestVarExpr)
+            .setReturnType(apiFutureType)
+            .build();
+    AssignmentExpr apiFutureAssignmentExpr =
+        AssignmentExpr.builder()
+            .setVariableExpr(apiFutureVarExpr.toBuilder().setIsDecl(true).build())
+            .setValueExpr(pagedCallableFutureMethodExpr)
+            .build();
+    bodyExprs.add(apiFutureAssignmentExpr);
+
+    List<Statement> bodyStatements =
+        bodyExprs.stream().map(e -> ExprStatement.withExpr(e)).collect(Collectors.toList());
+    bodyExprs.clear();
+
+    // Add line comment
+    bodyStatements.add(CommentStatement.withComment(LineComment.withComment("Do something.")));
+
+    // For-loop on repeated response element
+    // e.g. for (ListExclusionsResponse element : future.get().iterateAll()) {
+    //        // doThingsWith(element);
+    //      }
+    VariableExpr repeatedResponseVarExpr =
+        VariableExpr.withVariable(
+            Variable.builder().setName("element").setType(repeatedResponseType).build());
+    MethodInvocationExpr futureGetIterateAllMethodExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(apiFutureVarExpr)
+            .setMethodName("get")
+            .build();
+    futureGetIterateAllMethodExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(futureGetIterateAllMethodExpr)
+            .setMethodName("iterateAll")
+            .setReturnType(repeatedResponseType)
+            .build();
+    CommentStatement lineCommentStatement =
+        CommentStatement.withComment(LineComment.withComment("doThingsWith(element);"));
+    ForStatement repeatedResponseForStatement =
+        ForStatement.builder()
+            .setLocalVariableExpr(repeatedResponseVarExpr.toBuilder().setIsDecl(true).build())
+            .setCollectionExpr(futureGetIterateAllMethodExpr)
+            .setBody(Arrays.asList(lineCommentStatement))
+            .build();
+    bodyStatements.add(repeatedResponseForStatement);
+
+    return SampleCodeWriter.write(
+        TryCatchStatement.builder()
+            .setTryResourceExpr(assignClientVariableWithCreateMethodExpr(clientVarExpr))
+            .setTryBody(bodyStatements)
+            .setIsSampleCode(true)
+            .build());
+  }
+
   private static List<Statement> composeUnaryRpcMethodSampleCodeBodyStatements(
       Method method,
       VariableExpr clientVarExpr,
diff --git a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
index b9585ec489..8aee6f2f12 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
+++ b/src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClient.golden
@@ -377,7 +377,25 @@ public class EchoClient implements BackgroundResource {
   }
 
   // AUTO-GENERATED DOCUMENTATION AND METHOD.
-  /** Sample code: */
+  /**
+   * Sample code:
+   *
+   * <pre>{@code
+   * try (EchoClient echoClient = EchoClient.create()) {
+   *   PagedExpandRequest request =
+   *       PagedExpandRequest.newBuilder()
+   *           .setContent("content951530617")
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<EchoResponse> future = echoClient.pagedExpandPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (EchoResponse element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
+   */
   public final UnaryCallable<PagedExpandRequest, PagedExpandPagedResponse>
       pagedExpandPagedCallable() {
     return stub.pagedExpandPagedCallable();
@@ -435,7 +453,26 @@ public class EchoClient implements BackgroundResource {
   }
 
   // AUTO-GENERATED DOCUMENTATION AND METHOD.
-  /** Sample code: */
+  /**
+   * Sample code:
+   *
+   * <pre>{@code
+   * try (EchoClient echoClient = EchoClient.create()) {
+   *   PagedExpandRequest request =
+   *       PagedExpandRequest.newBuilder()
+   *           .setContent("content951530617")
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<EchoResponse> future =
+   *       echoClient.simplePagedExpandPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (EchoResponse element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
+   */
   public final UnaryCallable<PagedExpandRequest, SimplePagedExpandPagedResponse>
       simplePagedExpandPagedCallable() {
     return stub.simplePagedExpandPagedCallable();
diff --git a/src/test/java/com/google/api/generator/gapic/composer/goldens/IdentityClient.golden b/src/test/java/com/google/api/generator/gapic/composer/goldens/IdentityClient.golden
index cfc332034f..07dc235155 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/goldens/IdentityClient.golden
+++ b/src/test/java/com/google/api/generator/gapic/composer/goldens/IdentityClient.golden
@@ -405,7 +405,24 @@ public class IdentityClient implements BackgroundResource {
   }
 
   // AUTO-GENERATED DOCUMENTATION AND METHOD.
-  /** Sample code: */
+  /**
+   * Sample code:
+   *
+   * <pre>{@code
+   * try (IdentityClient identityClient = IdentityClient.create()) {
+   *   ListUsersRequest request =
+   *       ListUsersRequest.newBuilder()
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<User> future = identityClient.listUsersPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (User element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
+   */
   public final UnaryCallable<ListUsersRequest, ListUsersPagedResponse> listUsersPagedCallable() {
     return stub.listUsersPagedCallable();
   }
diff --git a/test/integration/goldens/asset/AssetServiceClient.java b/test/integration/goldens/asset/AssetServiceClient.java
index 6a39beb127..89dd018fdb 100644
--- a/test/integration/goldens/asset/AssetServiceClient.java
+++ b/test/integration/goldens/asset/AssetServiceClient.java
@@ -737,6 +737,26 @@ public final SearchAllResourcesPagedResponse searchAllResources(
    * on the desired scope, otherwise the request will be rejected.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (AssetServiceClient assetServiceClient = AssetServiceClient.create()) {
+   *   SearchAllResourcesRequest request =
+   *       SearchAllResourcesRequest.newBuilder()
+   *           .setScope("scope109264468")
+   *           .setQuery("query107944136")
+   *           .addAllAssetTypes(new ArrayList<String>())
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .setOrderBy("orderBy-1207110587")
+   *           .build();
+   *   ApiFuture<ResourceSearchResult> future =
+   *       assetServiceClient.searchAllResourcesPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (ResourceSearchResult element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<SearchAllResourcesRequest, SearchAllResourcesPagedResponse>
       searchAllResourcesPagedCallable() {
@@ -858,6 +878,24 @@ public final SearchAllIamPoliciesPagedResponse searchAllIamPolicies(
    * permission on the desired scope, otherwise the request will be rejected.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (AssetServiceClient assetServiceClient = AssetServiceClient.create()) {
+   *   SearchAllIamPoliciesRequest request =
+   *       SearchAllIamPoliciesRequest.newBuilder()
+   *           .setScope("scope109264468")
+   *           .setQuery("query107944136")
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<IamPolicySearchResult> future =
+   *       assetServiceClient.searchAllIamPoliciesPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (IamPolicySearchResult element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<SearchAllIamPoliciesRequest, SearchAllIamPoliciesPagedResponse>
       searchAllIamPoliciesPagedCallable() {
diff --git a/test/integration/goldens/library/LibraryServiceClient.java b/test/integration/goldens/library/LibraryServiceClient.java
index 67c5a4a57b..7a569548f2 100644
--- a/test/integration/goldens/library/LibraryServiceClient.java
+++ b/test/integration/goldens/library/LibraryServiceClient.java
@@ -324,6 +324,21 @@ public final ListShelvesPagedResponse listShelves(ListShelvesRequest request) {
    * necessarily be added to the end of this list.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (LibraryServiceClient libraryServiceClient = LibraryServiceClient.create()) {
+   *   ListShelvesRequest request =
+   *       ListShelvesRequest.newBuilder()
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<Shelf> future = libraryServiceClient.listShelvesPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (Shelf element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListShelvesRequest, ListShelvesPagedResponse>
       listShelvesPagedCallable() {
@@ -827,6 +842,22 @@ public final ListBooksPagedResponse listBooks(ListBooksRequest request) {
    * exist.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (LibraryServiceClient libraryServiceClient = LibraryServiceClient.create()) {
+   *   ListBooksRequest request =
+   *       ListBooksRequest.newBuilder()
+   *           .setName("name3373707")
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<Book> future = libraryServiceClient.listBooksPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (Book element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListBooksRequest, ListBooksPagedResponse> listBooksPagedCallable() {
     return stub.listBooksPagedCallable();
diff --git a/test/integration/goldens/logging/ConfigClient.java b/test/integration/goldens/logging/ConfigClient.java
index 8f3b649b27..0deaeb413b 100644
--- a/test/integration/goldens/logging/ConfigClient.java
+++ b/test/integration/goldens/logging/ConfigClient.java
@@ -366,6 +366,24 @@ public final ListBucketsPagedResponse listBuckets(ListBucketsRequest request) {
    * Lists buckets (Beta).
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (ConfigClient configClient = ConfigClient.create()) {
+   *   ListBucketsRequest request =
+   *       ListBucketsRequest.newBuilder()
+   *           .setParent(
+   *               LogBucketName.ofProjectLocationBucketName("[PROJECT]", "[LOCATION]", "[BUCKET]")
+   *                   .toString())
+   *           .setPageToken("pageToken873572522")
+   *           .setPageSize(883849137)
+   *           .build();
+   *   ApiFuture<LogBucket> future = configClient.listBucketsPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (LogBucket element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListBucketsRequest, ListBucketsPagedResponse>
       listBucketsPagedCallable() {
@@ -633,6 +651,22 @@ public final ListSinksPagedResponse listSinks(ListSinksRequest request) {
    * Lists sinks.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (ConfigClient configClient = ConfigClient.create()) {
+   *   ListSinksRequest request =
+   *       ListSinksRequest.newBuilder()
+   *           .setParent(LogSinkName.ofProjectSinkName("[PROJECT]", "[SINK]").toString())
+   *           .setPageToken("pageToken873572522")
+   *           .setPageSize(883849137)
+   *           .build();
+   *   ApiFuture<LogSink> future = configClient.listSinksPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (LogSink element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListSinksRequest, ListSinksPagedResponse> listSinksPagedCallable() {
     return stub.listSinksPagedCallable();
@@ -1424,6 +1458,24 @@ public final ListExclusionsPagedResponse listExclusions(ListExclusionsRequest re
    * Lists all the exclusions in a parent resource.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (ConfigClient configClient = ConfigClient.create()) {
+   *   ListExclusionsRequest request =
+   *       ListExclusionsRequest.newBuilder()
+   *           .setParent(
+   *               LogExclusionName.ofProjectExclusionName("[PROJECT]", "[EXCLUSION]").toString())
+   *           .setPageToken("pageToken873572522")
+   *           .setPageSize(883849137)
+   *           .build();
+   *   ApiFuture<LogExclusion> future =
+   *       configClient.listExclusionsPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (LogExclusion element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListExclusionsRequest, ListExclusionsPagedResponse>
       listExclusionsPagedCallable() {
diff --git a/test/integration/goldens/logging/LoggingClient.java b/test/integration/goldens/logging/LoggingClient.java
index db2dcc3bdc..45467735be 100644
--- a/test/integration/goldens/logging/LoggingClient.java
+++ b/test/integration/goldens/logging/LoggingClient.java
@@ -535,6 +535,24 @@ public final ListLogEntriesPagedResponse listLogEntries(ListLogEntriesRequest re
    * Logs](https://cloud.google.com/logging/docs/export).
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (LoggingClient loggingClient = LoggingClient.create()) {
+   *   ListLogEntriesRequest request =
+   *       ListLogEntriesRequest.newBuilder()
+   *           .addAllResourceNames(new ArrayList<String>())
+   *           .setFilter("filter-1274492040")
+   *           .setOrderBy("orderBy-1207110587")
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<LogEntry> future = loggingClient.listLogEntriesPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (LogEntry element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListLogEntriesRequest, ListLogEntriesPagedResponse>
       listLogEntriesPagedCallable() {
@@ -587,6 +605,22 @@ public final ListMonitoredResourceDescriptorsPagedResponse listMonitoredResource
    * Lists the descriptors for monitored resource types used by Logging.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (LoggingClient loggingClient = LoggingClient.create()) {
+   *   ListMonitoredResourceDescriptorsRequest request =
+   *       ListMonitoredResourceDescriptorsRequest.newBuilder()
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<MonitoredResourceDescriptor> future =
+   *       loggingClient.listMonitoredResourceDescriptorsPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (MonitoredResourceDescriptor element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<
           ListMonitoredResourceDescriptorsRequest, ListMonitoredResourceDescriptorsPagedResponse>
@@ -774,6 +808,22 @@ public final ListLogsPagedResponse listLogs(ListLogsRequest request) {
    * entries are listed.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (LoggingClient loggingClient = LoggingClient.create()) {
+   *   ListLogsRequest request =
+   *       ListLogsRequest.newBuilder()
+   *           .setParent(LogName.ofProjectLogName("[PROJECT]", "[LOG]").toString())
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<String> future = loggingClient.listLogsPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (String element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListLogsRequest, ListLogsPagedResponse> listLogsPagedCallable() {
     return stub.listLogsPagedCallable();
diff --git a/test/integration/goldens/logging/MetricsClient.java b/test/integration/goldens/logging/MetricsClient.java
index c3a53ec4b8..0c5310dc93 100644
--- a/test/integration/goldens/logging/MetricsClient.java
+++ b/test/integration/goldens/logging/MetricsClient.java
@@ -231,6 +231,22 @@ public final ListLogMetricsPagedResponse listLogMetrics(ListLogMetricsRequest re
    * Lists logs-based metrics.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (MetricsClient metricsClient = MetricsClient.create()) {
+   *   ListLogMetricsRequest request =
+   *       ListLogMetricsRequest.newBuilder()
+   *           .setParent(ProjectName.of("[PROJECT]").toString())
+   *           .setPageToken("pageToken873572522")
+   *           .setPageSize(883849137)
+   *           .build();
+   *   ApiFuture<LogMetric> future = metricsClient.listLogMetricsPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (LogMetric element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListLogMetricsRequest, ListLogMetricsPagedResponse>
       listLogMetricsPagedCallable() {
diff --git a/test/integration/goldens/redis/CloudRedisClient.java b/test/integration/goldens/redis/CloudRedisClient.java
index bf6aba5541..e8701aa91d 100644
--- a/test/integration/goldens/redis/CloudRedisClient.java
+++ b/test/integration/goldens/redis/CloudRedisClient.java
@@ -298,6 +298,23 @@ public final ListInstancesPagedResponse listInstances(ListInstancesRequest reque
    * are queried, and the results are aggregated.
    *
    * <p>Sample code:
+   *
+   * <pre>{@code
+   * try (CloudRedisClient cloudRedisClient = CloudRedisClient.create()) {
+   *   ListInstancesRequest request =
+   *       ListInstancesRequest.newBuilder()
+   *           .setParent(LocationName.of("[PROJECT]", "[LOCATION]").toString())
+   *           .setPageSize(883849137)
+   *           .setPageToken("pageToken873572522")
+   *           .build();
+   *   ApiFuture<Instance> future =
+   *       cloudRedisClient.listInstancesPagedCallable().futureCall(request);
+   *   // Do something.
+   *   for (Instance element : future.get().iterateAll()) {
+   *     // doThingsWith(element);
+   *   }
+   * }
+   * }</pre>
    */
   public final UnaryCallable<ListInstancesRequest, ListInstancesPagedResponse>
       listInstancesPagedCallable() {

From 943f746b0fa3d6a478f1e3f7ea74d831557a278f Mon Sep 17 00:00:00 2001
From: summerji <summerji@google.com>
Date: Thu, 17 Dec 2020 16:53:59 -0800
Subject: [PATCH 7/7] Add unit tests

---
 .../ServiceClientSampleCodeComposerTest.java  | 176 ++++++++++++++++++
 1 file changed, 176 insertions(+)

diff --git a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
index 441bea4c65..f06dc49390 100644
--- a/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
+++ b/src/test/java/com/google/api/generator/gapic/composer/ServiceClientSampleCodeComposerTest.java
@@ -1505,4 +1505,180 @@ public void validComposeLroCallableMethodHeaderSampleCode_withReturnVoid() {
             "}");
     assertEquals(results, expected);
   }
+
+  // ================================Paged Callable Method Sample Code ====================//
+  @Test
+  public void validComposePagedCallableMethodHeaderSampleCode() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("PagedExpandRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("PagedExpandResponse")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    Method method =
+        Method.builder()
+            .setName("PagedExpand")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setIsPaged(true)
+            .build();
+    String results =
+        ServiceClientSampleCodeComposer.composePagedCallableMethodHeaderSampleCode(
+            method, clientType, resourceNames, messageTypes);
+    String expected =
+        LineFormatter.lines(
+            "try (EchoClient echoClient = EchoClient.create()) {\n",
+            "  PagedExpandRequest request =\n",
+            "      PagedExpandRequest.newBuilder()\n",
+            "          .setContent(\"content951530617\")\n",
+            "          .setPageSize(883849137)\n",
+            "          .setPageToken(\"pageToken873572522\")\n",
+            "          .build();\n",
+            "  ApiFuture<EchoResponse> future = echoClient.pagedExpandPagedCallable().futureCall(request);\n",
+            "  // Do something.\n",
+            "  for (EchoResponse element : future.get().iterateAll()) {\n",
+            "    // doThingsWith(element);\n",
+            "  }\n",
+            "}");
+    assertEquals(results, expected);
+  }
+
+  @Test
+  public void invalidComposePagedCallableMethodHeaderSampleCode_inputTypeNotExistInMessage() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("NotExistRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("PagedExpandResponse")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    Method method =
+        Method.builder()
+            .setName("PagedExpand")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setIsPaged(true)
+            .build();
+    assertThrows(
+        NullPointerException.class,
+        () ->
+            ServiceClientSampleCodeComposer.composePagedCallableMethodHeaderSampleCode(
+                method, clientType, resourceNames, messageTypes));
+  }
+
+  @Test
+  public void invalidComposePagedCallableMethodHeaderSampleCode_noExistMethodResponse() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("NoExistResponse")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    Method method =
+        Method.builder()
+            .setName("PagedExpand")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setIsPaged(true)
+            .build();
+    assertThrows(
+        NullPointerException.class,
+        () ->
+            ServiceClientSampleCodeComposer.composePagedCallableMethodHeaderSampleCode(
+                method, clientType, resourceNames, messageTypes));
+  }
+
+  @Test
+  public void invalidComposePagedCallableMethodHeaderSampleCode_noRepeatedResponse() {
+    FileDescriptor echoFileDescriptor = EchoOuterClass.getDescriptor();
+    Map<String, ResourceName> resourceNames = Parser.parseResourceNames(echoFileDescriptor);
+    Map<String, Message> messageTypes = Parser.parseMessages(echoFileDescriptor);
+    TypeNode clientType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoClient")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode inputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("EchoRequest")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    TypeNode outputType =
+        TypeNode.withReference(
+            VaporReference.builder()
+                .setName("NoRepeatedResponse")
+                .setPakkage(SHOWCASE_PACKAGE_NAME)
+                .build());
+    Method method =
+        Method.builder()
+            .setName("PagedExpand")
+            .setInputType(inputType)
+            .setOutputType(outputType)
+            .setIsPaged(true)
+            .build();
+    Field responseField = Field.builder().setName("response").setType(TypeNode.STRING).build();
+    Message noRepeatedResponseMessage =
+        Message.builder()
+            .setName("NoRepeatedResponse")
+            .setType(
+                TypeNode.withReference(
+                    VaporReference.builder()
+                        .setName("NoRepeatedResponse")
+                        .setPakkage(SHOWCASE_PACKAGE_NAME)
+                        .build()))
+            .setFields(Arrays.asList(responseField))
+            .build();
+    messageTypes.put("NoRepeatedResponse", noRepeatedResponseMessage);
+    assertThrows(
+        NullPointerException.class,
+        () ->
+            ServiceClientSampleCodeComposer.composePagedCallableMethodHeaderSampleCode(
+                method, clientType, resourceNames, messageTypes));
+  }
 }