如何在Java注释处理器中获取正确的JavaFileManager？

Question

我已经编写了一个Java注释处理器,通过扩展javax.annotation.processing.AbstractProcessor在Eclipse上下文中调用它并且工作正常,除了我需要有关处理器工作的源路径和类路径的更多信息:

@SupportedAnnotationTypes({"MyAnno"})
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class Processor extends AbstractProcessor {

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        // this used to work in Java4 but not anymore (since Java6?):
        String sourcePath = processingEnv.getOptions().get("sourcepath");
        String classPath = processingEnv.getOptions().get("classpath");

        for (Element e : roundEnv.getElementsAnnotatedWith(MyAnno.class)) {
            myProcess(e, sourcePath, classPath); 
        }

        return true;
    }
}

问题是如何在注释处理上下文(实现process)中检索一个有效的JavaFileManager,它可以给出源路径和当前正在执行注释处理器的编译器的类路径.最好,我会找到一个不涉及对Eclipse/JDT特定接口的依赖的解决方案.

我已经试过这不以下不工作:

DiagnosticCollector<JavaFileObject> diagnostics =
                   new DiagnosticCollector<JavaFileObject>();
StandardJavaFileManager fm = ToolProvider.getSystemJavaCompiler().getStandardFileManager(diagnostics, null, null);
fm.getLocation(StandardLocation.CLASS_PATH); // prints an empty class path

Answer 1

对于 Java 8 及之前版本：

import com.sun.tools.javac.processing.JavacProcessingEnvironment;
import com.sun.tools.javac.util.Context;
import javax.annotation.processing.ProcessingEnvironment;

    protected static JavaFileManager getJavaFileManager(ProcessingEnvironment env) {
        JavaFileManager fm = null;

        if (env instanceof JavacProcessingEnvironment) {
            Context context = ((JavacProcessingEnvironment) env).getContext();

            fm = context.get(JavaFileManager.class);
        }

        return fm;
    }

对于 Java 9 和 10 以及更高版本（和 8），请使用反射来避免出现此 错误：

    protected static JavaFileManager getJavaFileManager(ProcessingEnvironment env) {
        JavaFileManager fm = null;

        try {
            /*
             * Context context = ((JavacProcessingEnvironment) env).getContext();
             */
            Method getContext = env.getClass().getMethod("getContext");
            Object context = getContext.invoke(env);
            /*
             * fm = context.get(JavaFileManager.class);
             */
            Method get = context.getClass().getMethod("get", Class.class);

            fm = (JavaFileManager) get.invoke(context, JavaFileManager.class);
        } catch (Exception exception) {
        }

        return fm;
    }