Java 寻找具有特定注解的方法及其注解元素

Question

假设我有这个注解类

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MethodXY {
    public int x();
    public int y();
}

public class AnnotationTest {
    @MethodXY(x=5, y=5)
    public void myMethodA(){ ... }

    @MethodXY(x=3, y=2)
    public void myMethodB(){ ... }
}

那么有没有办法查看一个对象，“寻找”带有@MethodXY 注释的方法，其中它的元素x = 3，y = 2，然后调用它？

谢谢

Answer 1

这是一个方法，它返回带有特定注释的方法:

public static List<Method> getMethodsAnnotatedWith(final Class<?> type, final Class<? extends Annotation> annotation) {
    final List<Method> methods = new ArrayList<Method>();
    Class<?> klass = type;
    while (klass != Object.class) { // need to traverse a type hierarchy in order to process methods from super types
        // iterate though the list of methods declared in the class represented by klass variable, and add those annotated with the specified annotation
        for (final Method method : klass.getDeclaredMethods()) {
            if (method.isAnnotationPresent(annotation)) {
                Annotation annotInstance = method.getAnnotation(annotation);
                // TODO process annotInstance
                methods.add(method);
            }
        }
        // move to the upper class in the hierarchy in search for more methods
        klass = klass.getSuperclass();
    }
    return methods;
}

它可以根据您的特定需求轻松修改。请注意，提供的方法会遍历类层次结构，以便找到具有所需注释的方法。

这是满足您特定需求的方法:

public static List<Method> getMethodsAnnotatedWithMethodXY(final Class<?> type) {
    final List<Method> methods = new ArrayList<Method>();
    Class<?> klass = type;
    while (klass != Object.class) { // need to iterated thought hierarchy in order to retrieve methods from above the current instance
        // iterate though the list of methods declared in the class represented by klass variable, and add those annotated with the specified annotation
        for (final Method method : klass.getDeclaredMethods()) {
            if (method.isAnnotationPresent(MethodXY.class)) {
                MethodXY annotInstance = method.getAnnotation(MethodXY.class);
                if (annotInstance.x() == 3 && annotInstance.y() == 2) {         
                    methods.add(method);
                }
            }
        }
        // move to the upper class in the hierarchy in search for more methods
        klass = klass.getSuperclass();
    }
    return methods;
}

对于找到的方法的调用请引用 tutorial .这里的潜在困难之一是方法参数的数量，它可能因找到的方法而异，因此需要一些额外的处理。