Java 11 module-info: 如何注册注解处理器

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英文:

Java 11 module-info: how to register an annotation processor

问题

要在Java 11中注册一个服务提供者,可以使用以下"provides"模块信息(module-info)条目:

module com.mycompany.mylib {

    provides ServiceInterface with ServiceImpl;

}

但是使用注解处理器似乎无法正常工作。(注解处理器的特殊之处在于,编译器应该在编译时选择实现,而不是在运行时选择应用程序。)

为了测试这一点,我在GitHub上创建了一些SSCCE

有两个模块:

  • java11-sample-annotation-processor:提供@Foo注解和FooApplicationProcessor
  • java11-sample-lib:提供两个示例类,都使用@Foo注解

预期输出:java11-sample-lib JAR中应该有一个foo.txt文件

master分支中的版本是有效的

  • Java 11
  • 未使用module-info
  • 注解处理器在src/main/resources/META-INF/services/javax.annotation.processing.Processor中注册

在以下版本中,不会生成foo.txt文件:

registration-in-module-info分支中,我将两个库更改为使用Java 11模块和module-info。在这里,注解处理器在module-info中注册:

import com.github.puce77.java11annotationprocessortest.annotation.impl.FooApplicationProcessor;

module com.github.puce77.java11annotationprocessortest.annotation {
    exports com.github.puce77.java11annotationprocessortest.annotation;

    provides javax.annotation.processing.Processor with FooApplicationProcessor;

    requires java.compiler;
}

registration-in-module-info-moduleAndPkg分支中,是一个轻微的变化,我指定了目标模块和目标包(硬编码),而不是根包。

registration-meta-inf分支中,两者仍然具有module-info,但是注解处理器是在src/main/resources/META-INF/services/javax.annotation.processing.Processor中注册,而不是在module-info中(如果编译器无法处理module-info中的provides语句怎么办!?)

only-one-module分支中,我再次从java11-sample-annotation-processor中删除了module-info。注解处理器在src/main/resources/META-INF/services/javax.annotation.processing.Processor中注册。

因此,我的问题是:在使用Java 11模块时,如何配置注解处理器?

英文:

To register a service provider in a Java 11 the following "provides" module-info entry can be used:

module com.mycompany.mylib {

    provides ServiceInterface with ServiceImpl;

}

With annotation processors this doesn't seem to work, however. (The special thing with annotation processors is that it's the compiler which should pick up the implementation during compile time rather than the application during runtime.)

To test this out, I've created some SSCCEs on GitHub.

There are 2 modules:

  • java11-sample-annotation-processor: provides the @Foo annotation and the FooApplicationProcessor
  • java11-sample-lib: provides 2 sample classes, both using the @Foo annotation

Expected output: in the java11-sample-lib JAR there should be a foo.txt file

The version in the master branch is the one that works:

  • Java 11
  • no module-info used
  • annotation processor registration in src/main/resources/META-INF/services/javax.annotation.processing.Processor

In the following versions the foo.txt file is not generated:

In the registration-in-module-info branch I've changed the 2 libs to Java 11 modules with module-info.
The annotation processor is here registered in the module-info:

import com.github.puce77.java11annotationprocessortest.annotation.impl.FooApplicationProcessor;

module com.github.puce77.java11annotationprocessortest.annotation {
    exports com.github.puce77.java11annotationprocessortest.annotation;

    provides javax.annotation.processing.Processor with FooApplicationProcessor;

    requires java.compiler;
}

The registration-in-module-info-moduleAndPkg branch is a slight variation, where I specified the target module and target package (hardcoded) rather than the root package.

In the registration-meta-inf branch still both have a module-info but the annotation processor is registered in src/main/resources/META-INF/services/javax.annotation.processing.Processor rather than in the module-info (in case the compiler can not work with provides statements in the module-info!?)

In the only-one-module branch I've removed the module-info from the java11-sample-annotation-processor again. The annotation processor is registered in src/main/resources/META-INF/services/javax.annotation.processing.Processor.

So my question: how can I configure an annotation processor when working with Java 11 modules?

答案1

得分: 4

过去,在编译过程中将注解处理器放置在类路径上时,注解处理器会被自动检测到。您可以从javac文档中看到这一点:

--class-path path-classpath path-cp path

指定查找用户类文件和注解处理器的位置 [已加重]。该类路径会覆盖CLASSPATH环境变量中的用户类路径。

  • 如果未指定 --class-path-classpath-cp,则用户类路径为CLASSPATH环境变量的值,如果设置了的话,否则为当前目录。
  • 如果未为模块编译代码,且未指定 --source-path-sourcepath 选项,则还会在用户类路径中查找源文件。
  • 如果未指定 -processorpath 选项,则也会在类路径中查找注解处理器 [已加重]

[...]

--processor-path path-processorpath path

指定查找注解处理器的位置。如果未使用此选项,则会在类路径中查找处理器 [已加重]

只要您使用类路径,这仍然适用。然而,在使用模块路径时情况就不同了。为了检测到模块化注解处理器,您必须使用另一个选项明确指向它们:

--module-path path-p path

指定查找应用程序模块的位置。

[...]

--processor-module-path path

指定用于查找注解处理器的模块路径。

没有提到会使用模块路径自动检测注解处理器。

英文:

It used to be that annotation processors were automatically detected when placed on the class-path during compilation. You can see this from the documentation of javac:

>--class-path path, -classpath path, or -cp path
>
> Specifies where to find user class files and annotation processors [emphasis added]. This class path overrides the user class path in the CLASSPATH environment variable.
>
>* If --class-path, -classpath, or -cp are not specified, then the user class path is the value of the CLASSPATH environment variable, if that is set, or else the current directory.
>* If not compiling code for modules, if the --source-path or -sourcepath option is not specified, then the user class path is also searched for source files.
>* If the -processorpath option is not specified, then the class path is also searched for annotation processors [emphasis added].
>
>[...]
>
>--processor-path path or -processorpath path
>
>Specifies where to find annotation processors. If this option is not used, then the class path is searched for processors [emphasis added].

And this is still the case as long as you're using the class-path. This is not the case, however, when using the module-path. For modular annotation processors to be detected you have to explicitly point to them with another option:

>--module-path path or -p path
>
>Specifies where to find application modules.
>
> [...]
>
>--processor-module-path path
>
>Specifies the module path used for finding annotation processors.

No mention of the module-path being used to automatically detect annotation processors.

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  • 本文由 发表于 2020年3月15日 21:07:51
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