第27 章 ： 反射与Annotation

120 反射取得Annotation信息

JDK > 1.5

不同的Annotation 有他的存在范围

public enum RetentionPolicy { SOURCE, CLASS, RUNTIME
}


  

 

  
1
  
2
  
3
  
4
  
5
  
6
 

import java.lang.annotation.Annotation;

@Deprecated
class Person{

}

class Demo{ public static void main(String[] args) { Annotation[] annotations = Person.class.getAnnotations(); for (Annotation a: annotations){ System.out.println(a); // @java.lang.Deprecated() } }
}

  

 

  
1
  
2
  
3
  
4
  
5
  
6
  
7
  
8
  
9
  
10
  
11
  
12
  
13
  
14
  
15
  
16
 

121 自定义Annotation

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

// 定义运行时策略
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation{ public String name(); public int age() default 23; // 设置默认值
}


class Message { @MyAnnotation(name="Tom") public void send(String msg){ System.out.println(msg); }
}

class Demo{ public static void main(String[] args) throws Exception { Method method = Message.class.getDeclaredMethod("send", String.class); MyAnnotation annotation = method.getAnnotation(MyAnnotation.class); String name = annotation.name(); // Tom int age = annotation.age();  // 23 String msg = String.format("[%s] %s ", name, age); method.invoke(Message.class.getDeclaredConstructor().newInstance(), msg); // [Tom] 23  }
}

  

 

  
1
  
2
  
3
  
4
  
5
  
6
  
7
  
8
  
9
  
10
  
11
  
12
  
13
  
14
  
15
  
16
  
17
  
18
  
19
  
20
  
21
  
22
  
23
  
24
  
25
  
26
  
27
  
28
  
29
  
30
  
31
  
32
 

122 工厂设计模式与Annotation整合

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

// 消息接口
interface IMessage { public void send(String msg);
}

// 消息实现类
class MessageImpl implements IMessage { public void send(String msg) { System.out.println("消息发送"); }
}


// 动态代理类
class MessageProxy implements InvocationHandler { private Object target; public Object bind(Object target) { this.target = target; return Proxy.newProxyInstance( target.getClass().getClassLoader(), target.getClass().getInterfaces(), this ); } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Object obj = null; if (this.connect()) { obj = method.invoke(this.target, args); } this.close(); return obj; } public boolean connect() { System.out.println("打开连接"); return true; } public void close() { System.out.println("关闭连接"); }

}

// 工厂类
class Factory { private Factory() { } public static <T> T getInstance(Class<T> clazz) { try { return (T) new MessageProxy().bind(clazz.getDeclaredConstructor().newInstance()); } catch (Exception e) { e.printStackTrace(); return null; } }
}

@Retention(RetentionPolicy.RUNTIME)
@interface UseMessage { public Class<?> clazz();
}

// 利用注解实现类的使用
@UseMessage(clazz = MessageImpl.class)
class MessageService { private IMessage message; public MessageService() { UseMessage use = MessageService.class.getAnnotation(UseMessage.class); this.message = (IMessage) Factory.getInstance(use.clazz()); } public void send(String msg) { this.message.send(msg); }
}

class Demo { public static void main(String[] args) { MessageService message = new MessageService(); message.send("发送消息"); }
}

  

 

  
1
  
2
  
3
  
4
  
5
  
6
  
7
  
8
  
9
  
10
  
11
  
12
  
13
  
14
  
15
  
16
  
17
  
18
  
19
  
20
  
21
  
22
  
23
  
24
  
25
  
26
  
27
  
28
  
29
  
30
  
31
  
32
  
33
  
34
  
35
  
36
  
37
  
38
  
39
  
40
  
41
  
42
  
43
  
44
  
45
  
46
  
47
  
48
  
49
  
50
  
51
  
52
  
53
  
54
  
55
  
56
  
57
  
58
  
59
  
60
  
61
  
62
  
63
  
64
  
65
  
66
  
67
  
68
  
69
  
70
  
71
  
72
  
73
  
74
  
75
  
76
  
77
  
78
  
79
  
80
  
81
  
82
  
83
  
84
  
85
  
86
  
87
  
88
  
89
  
90
  
91
  
92
  
93
  
94
  
95
  
96
  
97
 

文章来源: pengshiyu.blog.csdn.net，作者：彭世瑜，版权归原作者所有，如需转载，请联系作者。

原文链接：pengshiyu.blog.csdn.net/article/details/103789433