Maven example of annotation preprocessing and generation of classes in same compile process?

Question

Does anyone have a clean example of a maven project preprocessing class annotations at compile time with subsequent generation of classes to be compiled in the same compilation process?

Does anyone have a step-by-step procedure to implement such a project?

Solution 1

After navigating a lot in existing documentation on the net, I came up with the following:

What needs to be clarified:

• In order to process annotations on a given project P, you first need an annotation processor compiled in a separate library S. P should have a dependency on S.
• Implementing annotation processing in Java 5 is absolutely not the same thing as in Java 6.
• Java 5 relies on a separate execution of apt. The corresponding tutorials here and here help understanding the basics of annotation processing and implementation in Java 5. Good reading for newbies.
• Implementing annotation processing in Java 5 with Maven is tricky. One needs to add a local dependency to tools.jar to access the API described in these tutorials. Not clean. Some third-party plugins calling the apt are available, but not well documented.
• Those using Java 6 should not jump-start implementing their processors according to the above tutorials.

Annotation Processing in Java 6 with Maven

• A new package has been delivered in Java 6 to process annotations: the Pluggable Annotation Processing.
• To implement a processor, create a separate Maven project. The above tutorial or this one explains how to proceed. This is our library S.
• Then, create your project P and add a Maven dependency on S.
• There is currently an issue with the maven-compiler-plugin, but a workaround is available here. Use it to compile your generated code as part of existing annotated code.

...and code generation

• A great Java code generation library called CodeModel is available from Maven central. A good tutorial is available here. The javax annotation processing package offers some tools to generate output too.

Solution 2

maven-processor-plugin can do that...

https://code.google.com/p/maven-annotation-plugin/

Example from documentation:

<build> <plugins>
  <!-- Run annotation processors on src/main/java sources -->
  <plugin>
    <groupId>org.bsc.maven</groupId>
    <artifactId>maven-processor-plugin</artifactId>
    <executions>
      <execution>
        <id>process</id>
        <goals>
          <goal>process</goal>
        </goals>
        <phase>generate-sources</phase>
      </execution>
    </executions>
  </plugin>
  <!-- Disable annotation processors during normal compilation -->
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
      <compilerArgument>-proc:none</compilerArgument>
    </configuration>
  </plugin>
</plugins> </build>

Comments

[Jérôme Verstrynge]

Thanks, but honestly I think maven-antlr-plugin is overkill. Moreover, the site does not provide a complete example explaining how to solve the issue I raise. I am thinking more about something along the AnnotationProcessor.The maven-annotation-plugin looks interesting, but it is work-in-progress with incomplete documentation. Not helpful.

[Admin]

I don't think he was advocating using the antlr plugin directly, but looking at its source to see how it does what it does.

[user1050755]

There is a lot of good stuff in this answer. But one thing is NOT true: you can do it in one maven pass. Here is an example that also includes an annotation processor using JCodeModel: github.com/jjYBdx4IL/example-maven-project-setups/tree/maste‌​r/…

[Don Rhummy]

@user1050755 Thanks for a great suggestion. One question: why did you use that JCodeModel and not the official one? github.com/javaee/jaxb-codemodel