java 编程基础 注解 :可重复的注解
重复注解
Java8以前,同一个程序元素前最多只能使用一相同类型的注解;如果需要在同一个元素前使用多个相同类型的注解,则必须使用注解"容器"。例如在Struts开发中,有时需要在 Action 类上使用多个@Result注解。在 Java8 以前只能写成如下形式:
@Results({@Result(name="failure", location="failed.jsp"),
@Result(name="success ", location ="succ.jsp")
})
public Acton FooAction{ ... }
java8以后可以这样写
@Result(name="failure", location="failed.jsp"),@Result(name="success ", location ="succ.jsp")
public Acton FooAction{ ... }
1,首先定义我们需要重复的注解(@Repeatable(ActionTodos.class)就表示我们的注解是可重复的,并且重复的容器是ActionTodos)
package com.zmd.repeatAnotation;import java.lang.annotation.*;
/**
* @ClassName ActionTodo
* @projectName: object1
* @author: Zhangmingda
* @description: 可重复注解
* date: 2021/5/19.
*/
//@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(ActionTodos.class)
public @interface ActionTodo {
String actionListenerName();
}
2,容器注解定义:
package com.zmd.repeatAnotation;import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @ClassName ActionTodos
* @projectName: object1
* @author: Zhangmingda
* @description: 容器注解
* date: 2021/5/19.
*/
//容器
@Retention(RetentionPolicy.RUNTIME)
//@Target(ElementType.TYPE)
public @interface ActionTodos {
ActionTodo[] value();
}
3,具体的使用:
package com.zmd.repeatAnotation;import javax.swing.*;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
/**
* @ClassName UseRepeatable
* @projectName: object1
* @author: Zhangmingda
* @description: XXX
* date: 2021/5/19.
*/
@ActionTodo(actionListenerName = "打鸟")
@ActionTodo(actionListenerName = "掏蛋")
@ActionTodo(actionListenerName = "煮着吃")
public class UseRepeatable {
@ActionTodo(actionListenerName = "打鸟")
@ActionTodo(actionListenerName = "掏蛋")
@ActionTodo(actionListenerName = "煮着吃")
private static JButton okButton = new JButton("一石N鸟");
public static void main(String[] args) throws NoSuchFieldException {
/**
* 获取注解容器
*/
Annotation[] annotations = UseRepeatable.class.getAnnotations();
for (Annotation annotation : annotations){ //获取所有注解,包含容器注解
System.out.println(annotation); //获取所有注解,包含容器注解
}
Field okbtnField = UseRepeatable.class.getDeclaredField("okButton");
Annotation[] actions = okbtnField.getAnnotations(); //获取所有注解,包含容器注解
//ActionTodo[] actions = okbtnField.getAnnotationsByType(ActionTodo.class); //可重复注解
for (Annotation actionTodo :actions) {
System.out.println(actionTodo);
}
/**
* 获取注解类的重复注解
*/
ActionTodo[] actionTodos = UseRepeatable.class.getAnnotationsByType(ActionTodo.class);
for (ActionTodo actionTodo : actionTodos){
System.out.println(actionTodo);
}
/**
* 获取属性(类变量)的重复注解
*/
//获取变量反射对象
Field[] fields = UseRepeatable.class.getDeclaredFields();
//循环判断
for (Field field:fields){
field.setAccessible(true);
//是否被容器注解修饰
if (field.isAnnotationPresent(ActionTodos.class)){
//获取注解列表
ActionTodo[] actionTodos1 = field.getAnnotationsByType(ActionTodo.class);
for (ActionTodo actionTodo:actionTodos1){
System.out.println(actionTodo);
}
}
}
}
}
测试使用输出
@com.zmd.repeatAnotation.ActionTodos(value={@com.zmd.repeatAnotation.ActionTodo(actionListenerName="打鸟"), @com.zmd.repeatAnotation.ActionTodo(actionListenerName="掏蛋"), @com.zmd.repeatAnotation.ActionTodo(actionListenerName="煮着吃")})
@com.zmd.repeatAnotation.ActionTodos(value={@com.zmd.repeatAnotation.ActionTodo(actionListenerName="打鸟"), @com.zmd.repeatAnotation.ActionTodo(actionListenerName="掏蛋"), @com.zmd.repeatAnotation.ActionTodo(actionListenerName="煮着吃")})
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="打鸟")
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="掏蛋")
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="煮着吃")
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="打鸟")
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="掏蛋")
@com.zmd.repeatAnotation.ActionTodo(actionListenerName="煮着吃")
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