Add interface for enhancing logback events

google-cloud-contrib/google-cloud-logging-logback/src/main/java/com/google/cloud/logging/logback/LoggingAppender.java

@@ -67,12 +67,14 @@ public class LoggingAppender extends UnsynchronizedAppenderBase<ILoggingEvent> {
 
   private volatile Logging logging;
   private List<LoggingEnhancer> loggingEnhancers;
+  private List<LoggingEventEnhancer> loggingEventEnhancers;
   private WriteOption[] defaultWriteOptions;
 
   private Level flushLevel;
   private String log;
   private String resourceType;
   private Set<String> enhancerClassNames = new HashSet<>();
+  private Set<String> loggingEventEnhancerClassNames = new HashSet<>();
 
   /**
    * Batched logging requests get immediately flushed for logs at or above this level.
@@ -114,6 +116,11 @@ public void setResourceType(String resourceType) {
   public void addEnhancer(String enhancerClassName) {
     this.enhancerClassNames.add(enhancerClassName);
   }
+
+  public void addLoggingEventEnhancer(String enhancerClassName) {
+    this.loggingEventEnhancerClassNames.add(enhancerClassName);
+  }
+
 
   Level getFlushLevel() {
     return (flushLevel != null) ? flushLevel : Level.ERROR;
@@ -128,11 +135,19 @@ MonitoredResource getMonitoredResource(String projectId) {
   }
 
   List<LoggingEnhancer> getLoggingEnhancers() {
-    List<LoggingEnhancer> loggingEnhancers = new ArrayList<>();
-    if (enhancerClassNames != null) {
-      for (String enhancerClassName : enhancerClassNames) {
+    return getEnhancers(enhancerClassNames);
+  }
+
+  List<LoggingEventEnhancer> getLoggingEventEnhancers() {
+    return getEnhancers(loggingEventEnhancerClassNames);
+  }
+
+  <T> List<T> getEnhancers(Set<String> classNames) {
+    List<T> loggingEnhancers = new ArrayList<>();
+    if (classNames != null) {
+      for (String enhancerClassName : classNames) {
         if (enhancerClassName != null) {
-          LoggingEnhancer enhancer = getEnhancer(enhancerClassName);
+          T enhancer = getEnhancer(enhancerClassName);
           if (enhancer != null) {
             loggingEnhancers.add(enhancer);
           }
@@ -142,10 +157,10 @@ List<LoggingEnhancer> getLoggingEnhancers() {
     return loggingEnhancers;
   }
 
-  private LoggingEnhancer getEnhancer(String enhancerClassName) {
+  private <T> T getEnhancer(String enhancerClassName) {
     try {
-      Class<? extends LoggingEnhancer> clz =
-          (Class<? extends LoggingEnhancer>)
+      Class<T> clz =
+          (Class<T>)
               Loader.loadClass(enhancerClassName.trim());
       return clz.newInstance();
     } catch (Exception ex) {
@@ -170,6 +185,9 @@ public synchronized void start() {
     List<LoggingEnhancer> resourceEnhancers = MonitoredResourceUtil.getResourceEnhancers();
     loggingEnhancers.addAll(resourceEnhancers);
     loggingEnhancers.addAll(getLoggingEnhancers());
+    loggingEventEnhancers = new ArrayList<>();
+    loggingEventEnhancers.addAll(getLoggingEventEnhancers());
+
     super.start();
   }
 
@@ -227,6 +245,12 @@ private LogEntry logEntryFor(ILoggingEvent e) {
       }
     }
 
+    if (loggingEventEnhancers != null) {
+      for (LoggingEventEnhancer enhancer : loggingEventEnhancers) {
+        enhancer.enhanceLogEntry(builder, e);
+      }
+    }
+
     return builder.build();
   }
 

google-cloud-contrib/google-cloud-logging-logback/src/main/java/com/google/cloud/logging/logback/LoggingEventEnhancer.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2017 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.logging.logback;
+
+import com.google.cloud.logging.LogEntry;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+
+/**
+ * An enhancer for {@linkplain ILoggingEvent} log entries.
+ * Used to add custom labels to the {@link LogEntry.Builder}.
+ */
+public interface LoggingEventEnhancer {
+  void enhanceLogEntry(LogEntry.Builder builder, ILoggingEvent e);
+}