Message fort intéressant sur comment aggreger simplement la javadoc sous Maven2 en utilisant les options de javadoc : 
Following some recent post about javadoc aggregation, I tried to play with javadoc attachments and dependency unpacking with some success and it was quite easy. Here are the poms:
- For project exporting javadoc:
<?xml version="1.0"?><project>
 <parent>
   <artifactId>merging-javadoc</artifactId>
   <groupId>oqube.maven</groupId>
   <version>1.0-SNAPSHOT</version>
 </parent>
 <modelVersion>4.0.0</modelVersion>
 <groupId>oqube.maven.javadoc</groupId>
 <artifactId>project1</artifactId>
 <version>1.0-SNAPSHOT</version>
<build>
 <plugins>
  <plugin>
   <artifactId>maven-javadoc-plugin</artifactId>
    <executions>
    <execution>
     <id>attach-javadocs</id>
     <goals>
      <goal>jar</goal>
     </goals>
    </execution>
   </executions>
  </plugin>
 </plugins>
</build>
</project>
- For project importing javadoc:
<?xml version="1.0"?><project>
 <parent>
   <artifactId>merging-javadoc</artifactId>
   <groupId>oqube.maven</groupId>
   <version>1.0-SNAPSHOT</version>
 </parent>
 <modelVersion>4.0.0</modelVersion>
 <groupId>oqube.maven.javadoc</groupId>
 <artifactId>aggregate</artifactId>
 <version>1.0-SNAPSHOT</version>
 <build>
  <plugins>
   <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
     <execution>
      <id>unpack</id>
      <phase>package</phase>
      <goals>
       <goal>unpack</goal>
      </goals>
      <configuration>
       <artifactItems>
        <artifactItem>
         <groupId>oqube.maven.javadoc</groupId>
         <artifactId>project1</artifactId>
         <version>1.0-SNAPSHOT</version>
         <type>jar</type>
         <classifier>javadoc</classifier>
         <overWrite>true</overWrite>
         <outputDirectory>
          ${project.build.directory}/site/project1-docs/
         </outputDirectory>
        </artifactItem>
        <artifactItem>
         <groupId>oqube.maven.javadoc</groupId>
         <artifactId>project2</artifactId>
         <version>1.0-SNAPSHOT</version>
         <classifier>javadoc</classifier>
         <type>jar</type>
         <overWrite>true</overWrite>
         <outputDirectory>
          ${project.build.directory}/site/project2-docs/
         </outputDirectory>
        </artifactItem>
       </artifactItems>
       <outputDirectory>
        ${project.build.directory}/site/project2-docs/
       </outputDirectory>
     </configuration>
    </execution>
   </executions>
      </plugin>
 </plugins>
</build>
</project>
- It is then just a matter of adding links on site.xml:
<?xml version="1.0" encoding="ISO-8859-1"?>
<project name="Javadoc aggregation test">
<publishDate position="bottom" format="dd-MM-yyyy"/>
<body>
 <menu name="API Documentation">
  <item name="Project1" href="/project1-docs/index.html"/>
  <item name="Project2" href="/project2-docs/index.html"/>
 </menu>
</body>
</project>
Of course, this is not **true** aggregation, but it works fine. One could achieve true aggregation using similar technique but with:
- exporting sources
- unpackgin source files and tweaking javadoc plugin to use these as inputs