浅谈 Spring 框架
Spring框架是分模块存在，除了最核心的Spring Core Container(即Spring容器)是必要模块之外，其他模块都是可选，视需要而定。大约有20多个模块。
Spring的核心是控制反转（IoC）和面向切面（AOP）。
简单来说，Spring是一个分层的JavaSE/EE full-stack(一站式) 轻量级开源框架。
一般来说，Spring主要分为7个模块：
构建项目
文件目录：
代码：
配置文件：applicationContext.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"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="hello" class="com.neuedu.hello.HelloWorld"></bean>
<bean id="userDaoOracle" class="com.neuedu.dao.impl.UserDaoOracleImpl"></bean>
</beans>
Test.java
package com.neuedu.test;
import com.neuedu.hello.HelloWorld;
import com.neuedu.service.UserService;
import com.neuedu.dao.impl.UserDaoOracleImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main(String[] args) {
/*HelloWorld hw = new HelloWorld();
hw.say();*/
/*
ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
HelloWorld hw = (HelloWorld)ac.getBean("hello");
hw.say();
HelloWorld hw2 = (HelloWorld)ac.getBean("hello");
System.out.println(hw == hw2);*/
/*UserService us = new UserService();
us.save();*/
ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
UserDaoOracleImpl ud = (UserDaoOracleImpl)ac.getBean("userDaoOracle");
ud.save();
}
}
ClassPathXmlApplicationContext 创建了一个 spring 容器，在容器中加载了一个配置文件（applicationContext.xml）
通过配置文件可以读取到所有的bean标签（id/class)
通过 class 可以 new 一个对象，class.forName("com.neuedu.hello.HelloWorld").newInstance();
UserDao.java
package com.neuedu.dao;
public interface UserDao {
public void save();
}
UserService.java
package com.neuedu.service;
import com.neuedu.dao.UserDao;
import com.neuedu.dao.impl.UserDaoOracleImpl;
import com.neuedu.dao.impl.UserDaoMysqlImpl;
public class UserService {
//UserDaoOracleImpl dao = new UserDaoOracleImpl();
//UserDaoMysqlImpl udml = new UserDaoMysqlImpl();
UserDao dao = new UserDaoMysqlImpl();//new UserDaoOracleImpl();
public void save() {
dao.save();
//dao.insert();
}
}
UserDaoMysqlImpl.java
package com.neuedu.dao.impl;
import com.neuedu.dao.UserDao;
public class UserDaoMysqlImpl implements UserDao{
public void save() {
System.out.println("通过mysql数据库将用户信息保存到数据库中");
}
}
UserDaoOracleImpl.java
package com.neuedu.dao.impl;
import com.neuedu.dao.UserDao;
public class UserDaoOracleImpl implements UserDao{
public void save() {
System.out.println("通过oracle数据库将用户信息保存到数据库中");
}
/*public void insert() {
System.out.println("通过mysql数据库将用户信息保存到数据库中");
}*/
}
输出：
改进：控制反转（IOC）
上面的方法，UserDao 注入是通过 UserService 自身 new 一个 dao 实现类 下面方法 将控制权交给 sping 容器，因为Service 和
Dao 都在 spring中，故当 Service 需要 Dao 时，会自动将 dao 的实现类的对象放入 Service 中
<?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="hello" class="com.neuedu.hello.HelloWorld"></bean>
<bean id="userDaoOracle" class="com.neuedu.dao.impl.UserDaoOracleImpl"></bean>
<bean id="userService" class="com.neuedu.service.UserService">
<!-- SQL注入 -->
<property name="dao" ref="userDaoOracle"></property>
</bean>
</beans>
package com.neuedu.test;
import com.neuedu.hello.HelloWorld;
import com.neuedu.service.UserService;
import com.neuedu.dao.impl.UserDaoOracleImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
/*UserDaoOracleImpl ud = (UserDaoOracleImpl)ac.getBean("userDaoOracle");
ud.save();*/
UserService us = (UserService)ac.getBean("userService");
us.save();
}
}
package com.neuedu.service;
import com.neuedu.dao.UserDao;
import com.neuedu.dao.impl.UserDaoOracleImpl;
import com.neuedu.dao.impl.UserDaoMysqlImpl;
public class UserService {
//UserDaoOracleImpl dao = new UserDaoOracleImpl();
//UserDaoMysqlImpl udml = new UserDaoMysqlImpl();
//UserDao dao = new UserDaoMysqlImpl();//new UserDaoOracleImpl();
private UserDao dao;
public void save() {
dao.save();
//dao.insert();
}
public UserDao getDao() {
return dao;
}
public void setDao(UserDao dao) {
this.dao = dao;
}
}
好处：Service 和 Dao 彻底解耦，只需更改配置文件：applicationContext.xml中的调用即可
<?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="hello" class="com.neuedu.hello.HelloWorld"></bean>
<bean id="userDaoMysql" class="com.neuedu.dao.impl.UserDaoMysqlImpl"></bean>
<bean id="userDaoOracle" class="com.neuedu.dao.impl.UserDaoOracleImpl"></bean>
<bean id="userService" class="com.neuedu.service.UserService">
<!-- SQL注入 -->
<property name="dao" ref="userDaoMysql"></property>
</bean>
</beans>