spring依赖注入(IOC)——解析

1、spring依赖注入定义（IOC）

依赖注入也叫控制反转，它是指运行过程中，如果需要调用另外一个对象协助时，无需在代码中创建被调用者（实例对象），而是依赖于外部的注入；

依赖注入分两种类型：设置注入，构造注入。

2、依赖注入事例——设置注入

Human接口

package com.centit.service;

public interface Human {
	public void eat();
	public void ask();
}

Lanuage接口

package com.centit.service;

public interface Language {
	public String kind();
}

Chinese对Human的实现类，

package com.centit.serviceImpl;

import com.centit.service.Human;
import com.centit.service.Language;

public class Chinese implements Human {
	private Language language;
	@Override
	public void ask() {
		// TODO Auto-generated method stub
		System.out.println("我是中国人，说普通话");

		System.out.println(language.kind());

	}
	public Chinese() {
		
	}
	
	@Override
	public void eat() {
		// TODO Auto-generated method stub
		System.out.println("我是中国人，只吃中国菜");
	}

	public Language getLanguage() {
		return language;
	}
	//设置注入（依赖注入）
	public void setLanguage(Language language) {
		this.language = language;
	}
	
}

LanguageImpl是Language实现类

package com.centit.serviceImpl;

import com.centit.service.Language;

public class LanguageImpl implements Language {

	@Override
	public String kind() {
		// TODO Auto-generated method stub
		return "中国人也说英文";
	}

}

applicationContext.xml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:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

	<bean id="chinese" class="com.centit.serviceImpl.Chinese">
		<property name="language" ref="language"></property>
	</bean>
	<bean id="american" class="com.centit.serviceImpl.American"></bean>
	<bean id="language" class="com.centit.serviceImpl.LanguageImpl"></bean>
</beans>

Test测试类

package com.centit.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;

import com.centit.SessionFactory.SessionFactory;
import com.centit.service.Human;

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ApplicationContext ctx=new FileSystemXmlApplicationContext("src/applicationContext.xml");
		Human human=(Human)ctx.getBean("chinese");
		human.ask();
		human.eat();
		human=(Human)ctx.getBean("american");
		human.ask();
		human.eat();
	}

}

这就是设置注入的事例，

3、依赖注入——构造注入

构造注入和依赖注入的区别就在Chinese实现中，增加一个含参数的构造函数

public void ask() {
// TODO Auto-generated method stub
System.out.println("我是中国人，说普通话");
System.out.println(language.kind());
}
public Chinese() {

}
public Chinese(Language language) {
super();
this.language = language;
}
同时applicationContext.xml配置文件有点小区别

<?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:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

	<bean id="chinese" class="com.centit.serviceImpl.Chinese">
		<constructor-arg ref="language"></constructor-arg>
	</bean>
	<bean id="american" class="com.centit.serviceImpl.American"></bean>
	<bean id="language" class="com.centit.serviceImpl.LanguageImpl"></bean>
</beans>