Spring自动装配----注解装配----Spring自带的@Autowired注解

父类

package cn.ychx;public interface Person {public void sayHello();}

学生子类

package cn.ychx;public class Student implements Person {@Overridepublic void sayHello() {System.out.println("Hello! My name is Tom, I'm a Student.");}}

教师子类

package cn.ychx;public class Teacher implements Person {@Overridepublic void sayHello() {System.out.println("Hello! My name is Alice, I'm a Teacher.");}}

表演类

package cn.ychx;public interface Performer {public void perform();
}

玩游戏

package cn.ychx;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;public class PlayGame implements Performer {@Autowired(required=false)@Qualifier("student")private Person person;@Overridepublic void perform() {if (person == null) {System.out.println("Person is not exist.");return;}person.sayHello();}
}

配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsdhttp://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd"><!-- 启用注解支持 --><context:annotation-config/><bean id="student" class="cn.ychx.Student"/><bean id="teacher" class="cn.ychx.Teacher"/><bean id="playGame" class="cn.ychx.PlayGame"></bean>
</beans>

执行

package cn.ychx;import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test {private static ApplicationContext ctx;public static void main(String[] args) {ctx = new ClassPathXmlApplicationContext("applicationContext.xml");Performer performer = (Performer) ctx.getBean("playGame");if (performer != null) {performer.perform();} else {System.out.println("Object is null.");}}
}

执行结果

Hello! My name is Tom, I'm a Student.

通过修改@Qualifier("teacher")可以得到结果

Hello! My name is Alice, I'm a Teacher.

示例使用的是Spring自带的@Autowired注解，实现将Person的实现类（student或者teacher）注入PlayGame类的person属性中。

1.启用Spring注解支持

<context:annotation-config/>

2.@Autowired(required=false)注解

可以标注在属性，set方法，构造器上，使用byType寻找上下文的bean。可以看到示例中标注在属性上面，这时可以省略set方法，不受private的影响。

required=false说明Bean的注入不是必须的，也就是说可以删除配置文件中的student和teacher的Bean，这时PlayGame中的person属性为null

4.@Qualifier("student")注解

用来明确指定要使用的bean（双引号中的）是谁，为什么使用这个注解，因为可以满足PlayGame中的person属性的Bean不是唯一的，有两个分别是student和teacher，