Spring中DI配合接口编程

一：DI基本概念

依赖注入(DI)，是spring容器实现的基础，在spring-core模块中实现的。所谓DI，就是指对象是被动接受依赖类而不是自己主动去找，换句话说就是指对象不是从容器中查找它依赖的类，而是在容器实例化对象的时候主动将它依赖的类注入给它。

DI作用：

di配合接口编程，的确可以减少层(web层) 和业务层的耦合度.

二：案例-模拟大小写转换

1.编写接口代码

<span style="font-size:18px;">package com.cloud.di;

public interface ChangeLetter {
	public String change();
}</span>

2.编写2个接口实现类

LowerLetter.java

<span style="font-size:18px;">package com.cloud.di;
public class LowerLetter implements ChangeLetter{
	public String str;
	public String getStr() {
		return str;
	}
	public void setStr(String str) {
		this.str = str;
	}
	@Override
	public String change() {
		return str.toLowerCase();
	}
}</span>

UpperLetter.java

<span style="font-size:18px;">package com.cloud.di;
public class UpperLetter implements ChangeLetter{
	private String str;
	public String getStr() {
		return str;
	}
	public void setStr(String str) {
		this.str = str;
	}
	@Override
	public String change() {
		return str.toUpperCase();
	}
}</span>

3.编写Spring配置文件

<span style="font-size:18px;"><beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:aop="http://www.springframework.org/schema/aop" 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.xsd 
		http://www.springframework.org/schema/mvc 
		http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd 
		http://www.springframework.org/schema/context 
		http://www.springframework.org/schema/context/spring-context-3.2.xsd 
		http://www.springframework.org/schema/aop 
		http://www.springframework.org/schema/aop/spring-aop-3.2.xsd 
		http://www.springframework.org/schema/tx 
		http://www.springframework.org/schema/tx/spring-tx-3.2.xsd ">
	<bean id="chanegLetter1" class="com.cloud.di.UpperLetter">
		<property name="str" value="abcdef"></property>
	</bean>
	<bean id="chanegLetter2" class="com.cloud.di.LowerLetter">
		<property name="str" value="ABCDEF"></property>
	</bean>
</beans></span>

4.编写测试文件

<span style="font-size:18px;">package com.cloud.di;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
	/**
	 * 测试大小写字母的转换
	 */
	public static void main(String[] args) {
		ApplicationContext ac= new ClassPathXmlApplicationContext("applicationContext.xml");
		UpperLetter ul = (UpperLetter) ac.getBean("chanegLetter1");
		String changeRes1 = ul.change();
		System.out.println("小写->大写"+changeRes1);
		
		LowerLetter ll = (LowerLetter) ac.getBean("chanegLetter2");
		String changeRes2 = ll.change();
		System.out.println("大写->小写"+changeRes2);
	}
}</span>