spring_01<bean>的两种注入方式

spring的核心思想之一：控制反转也就是依赖注入。在spring的世界里，所有的java对象都是一个bean。程序中类和类之间的互相调用，不再是以往的new的创建。而是依靠spring容器通过反射读取xml配置文件中的一个个的bean来生成一个个的具体的实现类，供程序使用。同时将编程方式提升至面向接口编程。在一定程度上降低了程序的耦合。同时面向接口对后期功能的扩展以及修改降低了难度。只需要修改或增加实现类即可。

下面展示了spring注入bean的两种方式：设置注入、构造注入。

（1）设置注入。

接口Person.java

package com.demo.interfaces;

public interface Person {
public void drive();
}

实现类 Chinese.java

package com.demo.impls;

import com.demo.interfaces.Person;
import com.demo.interfaces.Shop;

public class Chinese implements Person{

private Shop shop;

public void setShop(Shop shop) {
this.shop = shop;
}

@Override
public void drive() {

System.out.println(shop.work());

}

}

接口Shop.java

package com.demo.interfaces;

public interface Shop {

public String work();

}

实现类SShop.java

package com.demo.impls;

import com.demo.interfaces.Shop;

public class Sshop implements Shop{

@Override
public String work() {
return "卖汽车";
}

}

spring 配置文件beans.xml

<?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-4.0.xsd"> 
<bean id="chinese" class="com.demo.impls.Chinese">
<property name="shop" ref="sshop"></property>
</bean>

<bean id="sshop" class="com.demo.impls.Sshop"></bean>

</beans>

测试类Test.java
public static void main(String[] args) {
ApplicationContext ctx = new    ClassPathXmlApplicationContext("beans.xml");
Person p =  ctx.getBean("chinese",Person.class);
p.drive();
}

最后输出结果：卖汽车。

这是第一种设值注入方式，也就是根据

<bean id="chinese" class="com.demo.impls.Chinese">
<property name="shop" ref="sshop"></property>
</bean>

中的name来指定调用Chinese实现类中的哪个set方法，ref指定set方法的传入参数。

（2）构造注入

接口Person.java

package com.demo.interfaces;

public interface Person {
public void drive();
}

实现类 Chinese.java

package com.demo.impls;

import com.demo.interfaces.Person;
import com.demo.interfaces.Shop;

public class Chinese implements Person{

private Shop shop;

public Chinese(Shop shop){
this.shop = shop;
}

@Override
public void drive() {

System.out.println(shop.work());

}

}

接口Shop.java

package com.demo.interfaces;

public interface Shop {

public String work();

}

实现类SShop.java

package com.demo.impls;

import com.demo.interfaces.Shop;

public class Sshop implements Shop{

@Override
public String work() {
return "卖汽车";
}

}

spring 配置文件beans.xml

<?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-4.0.xsd"> 
<bean id="chinese" class="com.demo.impls.Chinese">
<constructor-arg ref="sshop"></constructor-arg>
</bean>

<bean id="sshop" class="com.demo.impls.Sshop"></bean>

</beans>

测试类Test.java
public static void main(String[] args) {
ApplicationContext ctx = new    ClassPathXmlApplicationContext("beans.xml");
Person p =  ctx.getBean("chinese",Person.class);
p.drive();
}

最后输出结果：卖汽车。