反射 注解 应用

今天才知道Java的反射这么强大，可以完全不知道方法名、参数、返回值就能进行方法调用,而且还能拿到方法的返回值，遍历返回值中的集合等。

自定义注解：

package Reflect;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @ClassName TestMethod
 * @description:
 * @author: isquz
 * @time: 2020/10/20 22:08
 */
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface TestMethod {
    String params();
}

方法使用注解：

package Reflect;

import java.util.ArrayList;
import java.util.List;

/**
 * @ClassName MethodAnnotation
 * @description:
 * @author: isquz
 * @time: 2020/10/20 22:11
 */
public class MethodAnnotation {

    public List<String> returnParamList(){
        List<String> list = new ArrayList<>();
        list.add("String1");
        list.add("String2");
        list.add("String3");
        return list;
    }

    @TestMethod(params = "returnParamList")
    public void testMethodWithAnnotation(String s){
        System.out.println("获取注解传递的参数集合" + s);
    }
}

反射调用注解：

package Reflect;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Iterator;

/**
 * @ClassName TestMethodAnnotation
 * @description:
 * @author: isquz
 * @time: 2020/10/20 22:07
 */
public class TestMethodAnnotation {
    public static void main(String[] args) {
        Class<?> cls = MethodAnnotation.class;
        Method[] methods = cls.getDeclaredMethods();
        try {
            for(Method method:methods){
                TestMethod methodInfo = method.getAnnotation(TestMethod.class);
                if(methodInfo != null){
                    System.out.println("添加注解的方法名：" + method.getName());
                    String param = methodInfo.params();
                    Class<?>[] methodParamType = method.getParameterTypes();
                    String variable = methodParamType[0].getSimpleName();
                    System.out.println("测试方法所需参数类型：" + variable);
                    System.out.println("注解中参数来源方法：" + param);

                    Method paramMethod = cls.getDeclaredMethod(param);
                    Method testMethod = cls.getDeclaredMethod(method.getName(), variable.getClass());

                    Iterable<?> paramList = (Iterable<?>) paramMethod.invoke(cls.newInstance());
                    Iterator<?> iterator = paramList.iterator();
                    while (iterator.hasNext()){
                        testMethod.invoke(cls.newInstance(), iterator.next());
                    }
                }
            }
        }catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

    }
}