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

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深蓝 · Answer 1 · 2021-10-23T18:34:42+0000

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.