显示目录

Spring Hello World

项目的结构图

spring-beans.xml

叫做 Bean configuration file,定义 bean 的属性和其他 bean 之间的依赖,Spring 根据 bean 的定义生成 bean。

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<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="userDao" class="com.xtuer.dao.UserDaoMySqlImpl"/>
</beans>

UserDao

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package com.xtuer.dao;
public interface UserDao {
public void deleteUser(int id);
}

UserDaoMySqlImpl

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package com.xtuer.dao;
public class UserDaoMySqlImpl implements UserDao {
@Override
public void deleteUser(int id) {
System.out.println("UserDaoMySqlImpl.deleteUser()");
}
}

UserDaoOracleImpl

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package com.xtuer.dao;
public class UserDaoOracleImpl implements UserDao {
@Override
public void deleteUser(int id) {
System.out.println("UserDaoOracleImpl.deleteUser()");
}
}

HelloWorld

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import com.xtuer.dao.UserDao;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class HelloWorld {
@Test
public void test() {
// Spring 读取 bean 的定义文件并生成 bean
ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");
// 从 Spring IoC 容器里获取 bean
UserDao userDao = context.getBean("userDao", UserDao.class);
userDao.deleteUser(0);
}
}

输出

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UserDaoMySqlImpl.deleteUser()

更换 UserDao 的实现

<bean id="userDao" class="com.xtuer.dao.UserDaoMySqlImpl"/> 修改为
<bean id="userDao" class="com.xtuer.dao.UserDaoOracleImpl"/>,输出

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UserDaoOracleImpl.deleteUser()

把 UserDao 的实现从 UserDaoMySqlImpl 修改为 UserDaoOracleImpl,只需要修改 XML 配置文件,不需要修改代码。

Spring IoC + 接口 ==> 容易实现非侵入式的开发,扩展已有代码