Expand value interning optimization and fix XML factory transformer usage

api/maven-api-core/src/main/java/org/apache/maven/api/Constants.java

@@ -539,6 +539,16 @@ public final class Constants {
     public static final String MAVEN_VERSION_RANGE_RESOLVER_NATURE_OVERRIDE =
             "maven.versionRangeResolver.natureOverride";
 
+    /**
+     * Comma-separated list of XML contexts/fields to intern during POM parsing for memory optimization.
+     * When not specified, a default set of commonly repeated contexts will be used.
+     * Example: "groupId,artifactId,version,scope,type"
+     *
+     * @since 4.0.0
+     */
+    @Config
+    public static final String MAVEN_MODEL_BUILDER_INTERNS = "maven.modelBuilder.interns";
+
     /**
      * All system properties used by Maven Logger start with this prefix.
      *

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultModelXmlFactory.java

@@ -92,7 +92,9 @@ private Model doRead(XmlReaderRequest request) throws XmlReaderException {
                 source = new InputSource(
                         request.getModelId(), path != null ? path.toUri().toString() : null);
             }
-            MavenStaxReader xml = new MavenStaxReader();
+            MavenStaxReader xml = request.getTransformer() != null
+                    ? new MavenStaxReader(request.getTransformer()::transform)
+                    : new MavenStaxReader();
             xml.setAddDefaultEntities(request.isAddDefaultEntities());
             if (inputStream != null) {
                 return xml.read(inputStream, request.isStrict(), source);

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultPluginXmlFactory.java

@@ -56,7 +56,9 @@ public PluginDescriptor read(@Nonnull XmlReaderRequest request) throws XmlReader
             throw new IllegalArgumentException("path, url, reader or inputStream must be non null");
         }
         try {
-            PluginDescriptorStaxReader xml = new PluginDescriptorStaxReader();
+            PluginDescriptorStaxReader xml = request.getTransformer() != null
+                    ? new PluginDescriptorStaxReader(request.getTransformer()::transform)
+                    : new PluginDescriptorStaxReader();
             xml.setAddDefaultEntities(request.isAddDefaultEntities());
             if (inputStream != null) {
                 return xml.read(inputStream, request.isStrict());

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultSettingsXmlFactory.java

@@ -55,7 +55,9 @@ public Settings read(@Nonnull XmlReaderRequest request) throws XmlReaderExceptio
             if (request.getModelId() != null || request.getLocation() != null) {
                 source = new InputSource(request.getLocation());
             }
-            SettingsStaxReader xml = new SettingsStaxReader();
+            SettingsStaxReader xml = request.getTransformer() != null
+                    ? new SettingsStaxReader(request.getTransformer()::transform)
+                    : new SettingsStaxReader();
             xml.setAddDefaultEntities(request.isAddDefaultEntities());
             if (reader != null) {
                 return xml.read(reader, request.isStrict(), source);

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultToolchainsXmlFactory.java

@@ -57,7 +57,9 @@ public PersistedToolchains read(@Nonnull XmlReaderRequest request) throws XmlRea
             if (request.getModelId() != null || request.getLocation() != null) {
                 source = new InputSource(request.getLocation());
             }
-            MavenToolchainsStaxReader xml = new MavenToolchainsStaxReader();
+            MavenToolchainsStaxReader xml = request.getTransformer() != null
+                    ? new MavenToolchainsStaxReader(request.getTransformer()::transform)
+                    : new MavenToolchainsStaxReader();
             xml.setAddDefaultEntities(request.isAddDefaultEntities());
             if (reader != null) {
                 return xml.read(reader, request.isStrict(), source);

impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultModelBuilder.java

@@ -26,6 +26,7 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -1254,7 +1255,7 @@ Model doReadFileModel() throws ModelBuilderException {
                             .path(modelSource.getPath())
                             .rootDirectory(rootDirectory)
                             .inputStream(is)
-                            .transformer(new InliningTransformer())
+                            .transformer(new InterningTransformer(session))
                             .build());
                 } catch (XmlReaderException e) {
                     if (!strict) {
@@ -1267,7 +1268,7 @@ Model doReadFileModel() throws ModelBuilderException {
                                 .path(modelSource.getPath())
                                 .rootDirectory(rootDirectory)
                                 .inputStream(is)
-                                .transformer(new InliningTransformer())
+                                .transformer(new InterningTransformer(session))
                                 .build());
                     } catch (XmlReaderException ne) {
                         // still unreadable even in non-strict mode, rethrow original error
@@ -2144,23 +2145,94 @@ public R getRequest() {
         }
     }
 
-    static class InliningTransformer implements XmlReaderRequest.Transformer {
-        static final Set<String> CONTEXTS = Set.of(
+    static class InterningTransformer implements XmlReaderRequest.Transformer {
+        static final Set<String> DEFAULT_CONTEXTS = Set.of(
+                // Core Maven coordinates
                 "groupId",
                 "artifactId",
                 "version",
                 "namespaceUri",
                 "packaging",
+
+                // Dependency-related fields
                 "scope",
+                "type",
+                "classifier",
+
+                // Build and plugin-related fields
                 "phase",
+                "goal",
+                "execution",
+
+                // Repository-related fields
                 "layout",
                 "policy",
                 "checksumPolicy",
-                "updatePolicy");
+                "updatePolicy",
+
+                // Common metadata fields
+                "modelVersion",
+                "name",
+                "url",
+                "system",
+                "distribution",
+                "status",
+
+                // SCM fields
+                "connection",
+                "developerConnection",
+                "tag",
+
+                // Common enum-like values that appear frequently
+                "id",
+                "inherited",
+                "optional");
+
+        private final Set<String> contexts;
+
+        /**
+         * Creates an InterningTransformer with default contexts.
+         */
+        InterningTransformer() {
+            this.contexts = DEFAULT_CONTEXTS;
+        }
+
+        /**
+         * Creates an InterningTransformer with contexts from session properties.
+         *
+         * @param session the Maven session to read properties from
+         */
+        InterningTransformer(Session session) {
+            this.contexts = parseContextsFromSession(session);
+        }
+
+        private Set<String> parseContextsFromSession(Session session) {
+            String contextsProperty = session.getUserProperties().get(Constants.MAVEN_MODEL_BUILDER_INTERNS);
+            if (contextsProperty == null) {
+                contextsProperty = session.getSystemProperties().get(Constants.MAVEN_MODEL_BUILDER_INTERNS);
+            }
+
+            if (contextsProperty == null || contextsProperty.trim().isEmpty()) {
+                return DEFAULT_CONTEXTS;
+            }
+
+            return Arrays.stream(contextsProperty.split(","))
+                    .map(String::trim)
+                    .filter(s -> !s.isEmpty())
+                    .collect(Collectors.toSet());
+        }
 
         @Override
         public String transform(String input, String context) {
-            return CONTEXTS.contains(context) ? input.intern() : input;
+            return input != null && contexts.contains(context) ? input.intern() : input;
+        }
+
+        /**
+         * Get the contexts that will be interned by this transformer.
+         * Used for testing purposes.
+         */
+        Set<String> getContexts() {
+            return contexts;
         }
     }
 }