java - 注释 - 在构建时读取元素值

Question

是否可以在构建时读取注释元素的值？例如，如果我定义了以下注释:

public @interface State {
    String stage();
}

然后我在类中注释一个方法，如下所示:

public class Foo {
   @State(stage = "build")
   public String doSomething() {
      return "doing something";
   }
}

如何在构建时在注释处理器中读取@State 注释元素“阶段”的值？我有一个如下构建的处理器:

@SupportedAnnotationTypes(value = {"State"})
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class StageProcessor extends AbstractProcessor { 
    @Override
    public boolean process(Set<? extends TypeElement> elementTypes,
            RoundEnvironment roundEnv) {
        for (Element element : roundEnv.getRootElements()) {
               // ... logic to read the value of element 'stage' from
               // annotation 'State' in here.
        }
        return true;
    }
}

Answer 1

这不是最佳答案，因为我自己还没有这样做，但鉴于已经过去 3 个小时，我会尽力而为。

Overview of annotation processing

Unless annotation processing is disabled with the -proc:none option, the compiler searches for any annotation processors that are available. The search path can be specified with the -processorpath option; if it is not given, the user class path is used. Processors are located by means of service provider-configuration files named
META-INF/services/javax.annotation.processing.Processor on the search path. Such files should contain the names of any annotation processors to be used, listed one per line. Alternatively, processors can be specified explicitly, using the -processor option.

看来您需要在 META-INF/services 文件夹中创建一个名为 javax.annotation.processing.Processor 的文件，其中列出了注释的名称处理器，每行一个。

编辑:那么我相信读取注释的代码会像...

    for (Element element : roundEnv.getRootElements()) {
        State state = element.getAnnotation(State.class);
        if(state != null) {
            String stage = state.stage();
            System.out.println("The element " + element + " has stage " + stage);
        }
    }

可以找到注释处理器的真实示例 here .