Spring 理解IOC
纸上得来终觉浅
做笔记一个重要的问题是，在没有系统的掌握一项技能之前，无法系统的对其进行总结。 实际上，能够做的就是盲人摸象，一点点总结和记录，在回头的时候做更深入的总结和理解
1.初识Spring IOC
1) IOC即控制反转，inverse of control， 既然是反转，原来的控制权在哪里？，现在的控制权又在哪里？，如何反转。 首先看一张对IOC进行描述的图片：
可以这样来理解：类1中包含了类2，那么在类1实例化的时候，类2会进行实例化，而类2如何实例化是由类1控制的，这时候控制权在类1，如果采用Spring的控制反转的话，用一个文件来确定类1，类2的关系，采用文件综合的来指定类1，类2的关系的这种方式，叫做依赖注入(DI)。 IOC是思想，DI是实现。下面用代码来描述：
2)代码实现
A:传统方式
package com.roadArchitectWeb.dao;
public interface AnimalDao {
/*所有动物有一个说话的方法*/
public void say();
}
package com.roadArchitectWeb.dao;
public class CatDaoImpl implements AnimalDao{
String says="喵喵";
public void say(){
System.out.println("CatDaoImpl.say():"+says);
}
}
package com.roadArchitectWeb.dao;
public class DogDaoImpl implements AnimalDao{
String says="汪汪";
public void say() {
System.out.println("DogDaoImpl.say():"+says);
}
}
package com.roadArchitectWeb.dao;
class AnimalSay1{
AnimalDao animalDao = new CatDaoImpl();
public void Say(){
animalDao.say();
}
}
class AnimalSay2{
AnimalDao animalDao = new CatDaoImpl();
public void Say(){
animalDao.say();
}
}
class AnimalSay3{
AnimalDao animalDao = new CatDaoImpl();
public void Say(){
animalDao.say();
}
}
public class AnimalMain {
public static void main(String[] args) {
AnimalSay1 animalSay = new AnimalSay1();
animalSay.Say();
AnimalSay2 animalSay2 = new AnimalSay2();
animalSay2.Say();
AnimalSay3 animalSay3 = new AnimalSay3();
animalSay3.Say();
}
}
结果是：
CatDaoImpl.say():喵喵
CatDaoImpl.say():喵喵
CatDaoImpl.say():喵喵
B：Spring 配置方式
修改CatDaoImpl：
package com.roadArchitectWeb.dao;
public class CatDaoImpl implements AnimalDao{
/*这个时候并没有值，会有xml文件注入*/
private String says;
/*set方法，为了bean注入*/
public void setSays(String says) {
this.says = says;
}
public void say(){
System.out.println("CatDaoImpl.say():"+says);
}
/*一个无参的构造方法*/
public CatDaoImpl(){
}
}
修改AnimalMain：
package com.roadArchitectWeb.dao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
class AnimalSay1{
/*创建Spring的IOX容器对象*/
ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
/*从IOC容器中获取Bean实例*/
CatDaoImpl catDaoImpl = (CatDaoImpl)ctx.getBean("CatDaoImpl");
/*调用其中的say方法*/
AnimalDao animalDao = catDaoImpl;
public void Say(){
animalDao.say();
}
}
class AnimalSay2{
AnimalDao animalDao = new CatDaoImpl();
public void Say(){
animalDao.say();
}
}
class AnimalSay3{
AnimalDao animalDao = new CatDaoImpl();
public void Say(){
animalDao.say();
}
}
public class AnimalMain {
public static void main(String[] args) {
AnimalSay1 animalSay1 = new AnimalSay1();
animalSay1.Say();
}
}把AnimalSay1中实例化方式catDaoImpl实例化方式改为从xml文件中获取bean；
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="CatDaoImpl" class="com.roadArchitectWeb.dao.CatDaoImpl"> <property name="says" value="喵喵喵"></property> </bean> </beans>
CatDaoImpl.say():喵喵喵
2.Spring
上面代码会有这样一个问题，AnimalSay1如果实现类不是CatDaoImpl，而是DogDaoImpl， 当然我们可以在xml中再增加一个bean，然后在AnimalSay1中获取这个bean；不过如果这个步骤也采用注入的方法完成，那么在实现类由CatDaoImpl改为DogDaoImpl的时候，AnimalSay1将不做任何改动。 AnimalSay2和AnimalSay3同AnimalSay1
DogDaoImpl：
package com.roadArchitectWeb.dao;
public class DogDaoImpl implements AnimalDao{
private String says;
public void setSays(String says) {
this.says = says;
}
public void say() {
System.out.println("DogDaoImpl.say():"+says);
}
public DogDaoImpl(){
}
}
AnimalMain：
package com.roadArchitectWeb.dao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
class AnimalSay1{
private AnimalDao animalDao;
public void setAnimalDao(AnimalDao animalDao) {
this.animalDao = animalDao;
}
public void Say(){
animalDao.say();
}
public AnimalSay1(){
}
}
class AnimalSay2{
private AnimalDao animalDao;
public void setAnimalDao(AnimalDao animalDao) {
this.animalDao = animalDao;
}
public void Say(){
animalDao.say();
}
public AnimalSay2(){
}
}
class AnimalSay3{
private AnimalDao animalDao;
public void setAnimalDao(AnimalDao animalDao) {
this.animalDao = animalDao;
}
public void Say(){
animalDao.say();
}
public AnimalSay3(){
}
}
public class AnimalMain {
public static void main(String[] args) {
/*创建Spring的IOX容器对象*/
ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
/*从IOC容器中获取Bean实例*/
AnimalSay1 animalSay1 = (AnimalSay1)ctx.getBean("AnimalSay1");
/*调用其中的say方法*/
animalSay1.Say();
/*从IOC容器中获取Bean实例*/
AnimalSay2 animalSay2 = (AnimalSay2)ctx.getBean("AnimalSay2");
/*调用其中的say方法*/
animalSay2.Say();
/*从IOC容器中获取Bean实例*/
AnimalSay3 animalSay3 = (AnimalSay3)ctx.getBean("AnimalSay3");
/*调用其中的say方法*/
animalSay3.Say();
}
}
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="CatDaoImpl" class="com.roadArchitectWeb.dao.CatDaoImpl"> <property name="says" value="喵喵喵"></property> </bean> <bean id="DogDaoImpl" class="com.roadArchitectWeb.dao.CatDaoImpl"> <property name="says" value="汪汪汪"></property> </bean> <bean id="AnimalSay1" class="com.roadArchitectWeb.dao.AnimalSay1"> <property name="animalDao" ref="CatDaoImpl"></property> </bean> <bean id="AnimalSay2" class="com.roadArchitectWeb.dao.AnimalSay2"> <property name="animalDao" ref="DogDaoImpl"></property> </bean> <bean id="AnimalSay3" class="com.roadArchitectWeb.dao.AnimalSay3"> <property name="animalDao" ref="CatDaoImpl"></property> </bean> </beans>
结果如下：
CatDaoImpl.say():喵喵喵
CatDaoImpl.say():汪汪汪
CatDaoImpl.say():喵喵喵