一、Java還提供了4中註解，專門負責新註解的建立。

二、事例

    實現了註解的定義、使用註解進行類屬性值注入，廢話不多說，開始貼程式碼。

2.1 註解定義

package com.alex.annocation;

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

//註解的生命週期
@Retention(RetentionPolicy.RUNTIME)
//註解的作用範圍
@Target(ElementType.FIELD)
public @interface MyAnnocation {

	public String name() default "gaga";
	
	public int age() default 2;
}
 

2.2 Entity定義

package com.alex.annocation;

public class User {

	private String name;
	private int age;
	public void talk() {
		if (this.name.equals("alexZhang")) {
			System.out.println("我叫"+this.name+"，我今年"+this.age+"了，"+"劉濤，好漂亮，我好喜歡...");
		}else if(this.name.equals("liuTao")) {
			System.out.println("我叫"+this.name+"，我今年"+this.age+"了，"+"alex,你好帥，好像嫁給你...");
		}else {
			System.out.println("我叫"+this.name+"，我今年"+this.age+"了，"+"別說話，讓我靜靜的coding...");
		}
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
}
 

2.3 註解使用

package com.alex.annocation;

public class UserFactory {

	@MyAnnocation(name="liuTao",age=18)
	private User liu;
	@MyAnnocation(name="alexZhang",age=18)
	private User alex;
	@MyAnnocation
	private User man;
	public User getLiu() {
		return liu;
	}
	public void setLiu(User liu) {
		this.liu = liu;
	}
	public User getAlex() {
		return alex;
	}
	public void setAlex(User alex) {
		this.alex = alex;
	}
	public User getMan() {
		return man;
	}
	public void setMan(User man) {
		this.man = man;
	}
}

2.4 註解值注入實現

package com.alex.annocation;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class DealAnnocation {

	private static final UserFactory userFactory;
	
	static {
		userFactory = new UserFactory();
	}
	
	public static UserFactory getuserFactory() throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
		Field[] fields = userFactory.getClass().getDeclaredFields();
		if (fields != null && fields.length > 0 ) {
			for (Field field : fields) {
				MyAnnocation annotation = field.getAnnotation(MyAnnocation.class);
				String name = annotation.name();
				int age = annotation.age();
				field.setAccessible(true);
				Class<?> clazz = (Class<?>)field.getGenericType();
				Object object = clazz.newInstance();
				if (clazz.getName().equals("com.alex.annocation.User") && annotation != null ) {
					field.set(userFactory, object);
				}else {
					continue;
				}
				
				Method[] methods = clazz.getMethods();
				if ( methods != null && methods.length > 0 ) {
					for (Method umethod : methods) {
						if ("setName".equals(umethod.getName())) {
							umethod.invoke(object, name);
						}
						if ("setAge".equals(umethod.getName())) {
							umethod.invoke(object, age);
						}
					}
				}
			}
		}
		return userFactory;
	}
}

2.5  測試類

package com.alex.annocation;

public class MyMain {

	public static void main(String[] args) throws Exception {
		User alex = DealAnnocation.getuserFactory().getAlex();
		alex.talk();
		User liu = DealAnnocation.getuserFactory().getLiu();
		liu.talk();
		User man = DealAnnocation.getuserFactory().getMan();
		man.talk();
	}
}

2.6 執行Result

我叫alexZhang，我今年18了，劉濤，好漂亮，我好喜歡...
我叫liuTao，我今年18了，alex,你好帥，好像嫁給你...
我叫gaga，我今年2了，別說話，讓我靜靜的coding...

三、說明

    註解的使用很廣泛且方便