使用元注释触发注释处理器

Question

我已经建立了一个通过注释触发的注释处理器com.foo.FooEntity。有必要能够创建更多的构造型，以触发该注释处理器。

例如，控制器还应该触发此注释处理器。我想知道是否有一种方法可以@FooEntity在上面放置注释。就像是：

@FooEntity
@Target(TYPE)
@Retention(RUNTIME)
public @interface Controller {}

并使用它，以便此类触发注释处理

@Controller
public class MyController { ... }

当然，这里的想法是我想添加新的构造型，而不必接触注释处理器本身。

Answer 1

我不认为有可配置的处理器，处理的方式@FooEntity以及注释元注解与@FooEntity（@Controller在这种情况下）。相反，您可以做的是拥有一个支持任何注释（@SupportedAnnotationTypes("*")）的处理器，然后在处理器本身内实现一些其他逻辑，以便确定您要处理的注释。根据我对问题的理解，这是一个这样的实现：

package acme.annotation.processing;

import java.util.HashSet;
import java.util.Set;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.lang.model.element.TypeElement;

import acme.annotation.FooEntity;

@SupportedAnnotationTypes("*")
public class FooEntityExtendedProcessor extends AbstractProcessor {

    private void log(String msg) {
        System.out.println(msg);
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        log("Initially I was asked to process:" + annotations.toString());

        Set<TypeElement> fooAnnotations = new HashSet<>();
        for (TypeElement elem : annotations) {
            if (isFoo(elem)) fooAnnotations.add(elem);
        }

        if (fooAnnotations.size() > 0) {
            log("... but I am now going to process:" + fooAnnotations.toString());
            processInternal(fooAnnotations, roundEnv);
        } else {
            log("... but none of those was my business!");
        }

        // always return false so that other processors get a chance to process the annotations not consumed here
        return false;
    }

    private void processInternal(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        // TODO: do your foo processing here
    }

    private boolean isFoo(TypeElement elem) {
        if (elem.getQualifiedName().toString().equals("acme.annotation.FooEntity")
                || elem.getAnnotation(FooEntity.class) != null) {
            return true;            
        } else {
            return false;
        }
    }

}

样本运行将为您提供：

Initially I was asked to process:[acme.annotation.FooEntity, skriptor.annotation.ScriptArg, java.lang.Override, skriptor.annotation.ScriptCodeRT, skriptor.annotation.ScriptCode, skriptor.annotation.ScriptObject, javax.ws.rs.Path, javax.ws.rs.GET, acme.annotation.Controller, com.sun.jersey.spi.resource.Singleton, skriptor.annotation.ScriptImport, javax.ws.rs.ext.Provider, javax.ws.rs.Produces, javax.annotation.PostConstruct]
... but I am now going to process:[acme.annotation.Controller, acme.annotation.FooEntity]