Spring中DI配合接口编程

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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;}@Overridepublic 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;}@Overridepublic 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>

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