Java中,如何在外部获取方法参数的注解值?

Question

现有注解如下:

 package anno;

/**
 * Created by adinlead on 17-5-22.
 */
public @interface NoNull {
    boolean fields() default true;
}

方法如下:

package controllers;

import anno.NoNull;

/**
 * Created by adinlead on 17-5-22.
 */
public class Test {
    public static void test(@NoNull String str) {
        if (str == null){
            System.out.println("拦截失败");
        }
        System.out.println("拦截成功");
    }
}

在框架调用test之前,我可以手动写个方法来检查
我想在检查中获取test方法的参数是否带有@NoNull注解
应该怎么做?

Answer 1

 @Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface NoNull {
    boolean fields() default true;
}

 public class Test {
    public static void test(@NoNull String str) {
        if (str == null){
            System.out.println("拦截失败");
        }
        System.out.println("拦截成功");
    }
}

public class Demo1 {

    public static void main(String[] args) {
        f1(Test.class);
    }

    private static <T> void f1(Class<T> cls) {
        Method[] methods = cls.getDeclaredMethods();
        for (int i = 0; i < methods.length; i++) {
            Method method = methods[i];
            method.setAccessible(true);
            Parameter[] parameters = method.getParameters();
            for (int j = 0; j < parameters.length; j++) {
                Parameter parameter = parameters[j];
                Annotation[] annotations = parameter.getDeclaredAnnotations();
                for (int k = 0; k < annotations.length; k++) {
                    Annotation annotation = annotations[k];
                    System.out.println(annotation);
                }
            }
        }
    }
}