[MJAVADOC-697] Allowing to register alternative Javadoc implementation

src/main/java/org/apache/maven/plugins/javadoc/AbstractJavadocMojo.java

@@ -293,6 +293,9 @@ public abstract class AbstractJavadocMojo
     @Component
     private DependencyResolver dependencyResolver;
 
+    @Component
+    private List<JavadocImplementation> javadocInvocators;
+
     /**
      * Project builder
      *
@@ -5721,7 +5724,16 @@ private void executeJavadocCommandLine( Commandline cmd, File javadocOutputDirec
         CommandLineUtils.StringStreamConsumer out = new JavadocUtil.JavadocOutputStreamConsumer();
         try
         {
-            int exitCode = CommandLineUtils.executeCommandLine( cmd, out, err );
+            getLog().debug( "javadocInvocators: " + javadocInvocators );
+            int exitCode;
+            if ( javadocInvocators.isEmpty() )
+            {
+                exitCode = CommandLineUtils.executeCommandLine( cmd, out, err );
+            }
+            else
+            {
+                exitCode = javadocInvocators.get( 0 ).execute( cmd, out, err );
+            }
 
             String output = ( StringUtils.isEmpty( out.getOutput() ) ? null : '\n' + out.getOutput().trim() );
 

src/main/java/org/apache/maven/plugins/javadoc/JavadocImplementation.java

@@ -0,0 +1,39 @@
+package org.apache.maven.plugins.javadoc;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+import org.codehaus.plexus.util.cli.CommandLineException;
+import org.codehaus.plexus.util.cli.CommandLineUtils;
+
+/**
+ * Alternative way to invoke Javadoc. By default the system uses
+ * {@link CommandLineUtils#executeCommandLine}
+ * to invoke the {@code javadoc} command. By registering a different
+ * implementation of {@code JavadocImplementation}, one can change the way
+ * the {@code javadoc} tool is invoked.
+ */
+public interface JavadocImplementation
+{
+  int execute(
+        org.codehaus.plexus.util.cli.Commandline cmd, 
+        org.codehaus.plexus.util.cli.CommandLineUtils.StringStreamConsumer out, 
+        org.codehaus.plexus.util.cli.CommandLineUtils.StringStreamConsumer err
+  ) throws CommandLineException;
+}