转自：http://blessht.iteye.com/blog/1162131
平常的java开发中，程序员在某个类中需要依赖其它类的方法，则通常是new一个依赖类再调用类实例的方法，这种开发存在的问题是new的类实例不好统一管理，spring提出了依赖注入的思想，即依赖类不由程序员实例化，而是通过spring容器帮我们new指定实例并且将实例注入到需要该对象的类中。依赖注入的另一种说法是“控制反转”，通俗的理解是：平常我们new一个实例，这个实例的控制权是我们程序员，而控制反转是指new实例工作不由我们程序员来做而是交给spring容器来做。
spring有多种依赖注入的形式，下面仅介绍spring通过xml进行IOC配置的方式：
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Set注入
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package com.bless.springdemo.action;
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publicclass SpringAction {
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//注入对象springDao
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private SpringDao springDao;
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//一定要写被注入对象的set方法
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publicvoid setSpringDao(SpringDao springDao) {
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this.springDao = springDao;
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}
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}
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<!--配置bean,配置后该类由spring管理-->
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<bean name="springAction"class="com.bless.springdemo.action.SpringAction">
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<!--(1)依赖注入,配置当前类中相应的属性-->
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<property name="springDao" ref="springDao"></property>
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</bean>
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<bean name="springDao"class="com.bless.springdemo.dao.impl.SpringDaoImpl"></bean>
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构造器注入
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publicclass SpringAction {
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//注入对象springDao
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private SpringDao springDao;
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private User user;
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public SpringAction(SpringDao springDao,User user){
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this.springDao = springDao;
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this.user = user;
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System.out.println("构造方法调用springDao和user");
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}
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}
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<!--配置bean,配置后该类由spring管理-->
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<beanname="springAction"class="com.bless.springdemo.action.SpringAction">
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<!--(2)创建构造器注入,如果主类有带参的构造方法则需添加此配置-->
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<constructor-arg ref="springDao"></constructor-arg>
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<constructor-arg ref="user"></constructor-arg>
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</bean>
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<beanname="springDao"class="com.bless.springdemo.dao.impl.SpringDaoImpl"></bean>
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<beanname="user"class="com.bless.springdemo.vo.User"></bean>
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<beanname="springAction"class="com.bless.springdemo.action.SpringAction">
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<constructor-arg index="0" ref="springDao"></constructor-arg>
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<constructor-arg index="1" ref="user"></constructor-arg>
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</bean>
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<constructor-argtype="java.lang.String"ref=""/>
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静态工厂的方法注入
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package com.bless.springdemo.factory;
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import com.bless.springdemo.dao.FactoryDao;
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import com.bless.springdemo.dao.impl.FactoryDaoImpl;
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import com.bless.springdemo.dao.impl.StaticFacotryDaoImpl;
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publicclass DaoFactory {
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//静态工厂
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publicstaticfinal FactoryDao getStaticFactoryDaoImpl(){
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return new StaticFacotryDaoImpl();
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}
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}
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publicclass SpringAction {
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//注入对象
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private FactoryDao staticFactoryDao;
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publicvoid staticFactoryOk(){
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staticFactoryDao.saveFactory();
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}
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//注入对象的set方法
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publicvoid setStaticFactoryDao(FactoryDao staticFactoryDao) {
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this.staticFactoryDao = staticFactoryDao;
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}
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}
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<!--配置bean,配置后该类由spring管理-->
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<bean name="springAction" class="com.bless.springdemo.action.SpringAction">
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<!--(3)使用静态工厂的方法注入对象,对应下面的配置文件(3)-->
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<property name="staticFactoryDao" ref="staticFactoryDao"></property>
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</bean>
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<!--(3)此处获取对象的方式是从工厂类中获取静态方法-->
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<bean name="staticFactoryDao" class="com.bless.springdemo.factory.DaoFactory" factory-method="getStaticFactoryDaoImpl"></bean>
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实例工厂的方法注入
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publicclass DaoFactory {
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//实例工厂
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public FactoryDao getFactoryDaoImpl(){
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returnnew FactoryDaoImpl();
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}
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}
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publicclass SpringAction {
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//注入对象
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private FactoryDao factoryDao;
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publicvoid factoryOk(){
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factoryDao.saveFactory();
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}
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publicvoid setFactoryDao(FactoryDao factoryDao) {
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this.factoryDao = factoryDao;
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}
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}
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<!--配置bean,配置后该类由spring管理-->
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<beanname="springAction"class="com.bless.springdemo.action.SpringAction">
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<!--(4)使用实例工厂的方法注入对象,对应下面的配置文件(4)-->
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<propertyname="factoryDao"ref="factoryDao"></property>
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</bean>
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<!--(4)此处获取对象的方式是从工厂类中获取实例方法-->
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<beanname="daoFactory"class="com.bless.springdemo.factory.DaoFactory"></bean>
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<beanname="factoryDao"factory-bean="daoFactory"factory-method="getFactoryDaoImpl"></bean>
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总结
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<bean name="..."class="..." scope="prototype">
