Spring 实例化 bean 的方式
Set注入
构造器注入
静态工厂注入
实例化工厂注入
案例实操
Set注入
xml配置（同时spring也提供了对于基本数据类型的set注入方式）
<?xmlversion="1.0" encoding="UTF-8"?>
<beansxmlns="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">
<beanid="userDao"class="com.xxx.demo.UserDao"></bean>
<!-- setter注入 -->
<beanid="userService"class="com.xxx.demo.UserService">
<!--ref是对于外部bean对象引用，与被引用的bean对象的id保持一致-->
<propertyname="userDao"ref="userDao"></property>
</bean>
</beans>
UserDao.java
publicclassUserDao{
publicStringuserLogin() {
return "我是UserDao中的userLogin()的方法";
}
}
UserService.java
publicclassUserService{
//一定要提供属性的setter方法
privateUserDaouserDao;
publicvoiduserlogin() {
Stringres=userDao.userLogin();
System.out.println(res);
}
publicvoidsetUserDao(UserDaouserDao) {
this.userDao=userDao;
}
}
App.java
importorg.springframework.context.ApplicationContext;
importorg.springframework.context.support.ClassPathXmlApplicationContext;
publicclassApp{
publicstaticvoidmain(String[]args) {
ApplicationContextapplicationContext=newClassPathXmlApplicationContext("spring-config.xml");
UserServiceuserService=applicationContext.getBean("userService",UserService.class);
userService.userlogin();
}
}
构造器注入
xml配置（也提供对于基本数据类型、字符串等值的注入）
<?xmlversion="1.0" encoding="UTF-8"?>
<beansxmlns="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">
<beanid="userDao"class="com.xxx.demo.UserDao"></bean>
<!-- 构造器注入 -->
<beanid="userServiceV2"class="com.xxx.demo.UserServiceV2">
<constructor-argindex="0"ref="userDao"></constructor-arg>
<constructor-argindex="1"value="印度三哥"></constructor-arg>
</bean>
</beans>
构造器注入有三种形式：
index属性为参数顺序，如果只有一个参数index可以不设置。
name属性根据构造器中属性的名字。
type属性，是根据构造器中属性的类型来匹配的。如果相同类型属性不唯一，注入的属性按照顺序注入进来。
UserServiceV2.java类提供构造函数
/**
* 实现构造器注入
* @author Best Liu
*
*/
publicclassUserServiceV2{
privateUserDaouserDao;
privateStringname;
publicvoiduserlogin() {
Stringres=userDao.userLogin();
System.out.println(res);
System.out.println(name);
}
publicUserServiceV2(UserDaouserDao,Stringname) {
super();
this.userDao=userDao;
this.name=name;
}
}
静态工厂注入
xml配置
<?xmlversion="1.0"encoding="UTF-8"?>
<beansxmlns="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">
<!--静态工厂注入-->
<beanid="userDao01"class="com.xxx.demo.StaticFactory"factory-method="createuserDao"></bean>
<beanid="userService01"class="com.xxx.demo.UserService">
<propertyname="userDao"ref="userDao01"></property>
</bean>
</beans>
StaticFactory.java
publicclassStaticFactory{
publicstaticUserDaocreateuserDao(){
returnnewUserDao();
}
}
UserService.java
publicclassUserService{
privateUserDaouserDao;
publicvoiduserlogin() {
Stringres=userDao.userLogin();
System.out.println(res);
}
publicvoidsetUserDao(UserDaouserDao) {
this.userDao=userDao;
}
}
tips:静态工厂注入就是IoC静态工厂和DI的setter注入，将需要注入的属性对象利用静态工厂创建出来.
2.4 实例化工厂
xml配置
<?xmlversion="1.0" encoding="UTF-8"?>
<beansxmlns="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">
<!-- 实例化工厂 -->
<beanid="instanceFactory"class="com.xxx.demo.InstanceFactory"></bean>
<beanid="userDao3"factory-bean="instanceFactory"factory-method="createUserDao"></bean>
<beanid="userService02"class="com.xxx.demo.UserService">
<propertyname="userDao"ref="userDao3"></property>
</bean>
</beans>
InstanceFactory.java
publicclassInstanceFactory{
publicUserDaocreateUserDao(){
returnnewUserDao();
}
}
tips:重点掌握set，构造器注入，工厂方式了解即可，实际开发中基本使用set方式注入bean。
扩展
循环依赖的问题的产生
Bean通过构造器注入，之间彼此相互依赖对方导致bean无法实例化。
注入的选择：开发项目中set方式注入首选
使用构造注入可以在构建对象的同时一并完成依赖关系的建立，对象一建立则所有的一切也就准备好了，但如果要建立的对象关系很多，使用构造注入会在构建函数上留下一长串的参数，且不易记忆，这时使用Set注入会是个不错的选择。
使用Set注入可以有明确的名称，可以了解注入的对象会是什么，像setxxx()这样的名称比记忆Constructor上某个参数的位置代表某个对象更好。
xml配置
<?xmlversion="1.0" encoding="UTF-8"?>
<beansxmlns="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">
<beanid="goodsService"class="com.xxx.demo.GoodsService">
<!-- <constructor-arg index="0" ref="userService"></constructor-arg> -->
<propertyname="userService"ref="userService"></property>
</bean>
<beanid="userService"class="com.xxx.demo.UserService">
<!-- <constructor-arg index="0" ref="goodsService"></constructor-arg> -->
<propertyname="goodsService"ref="goodsService"></property>
</bean>
</beans>
GoodsService.java
publicclassGoodsService{
privateUserServiceuserService;
/*public GoodsService(UserService userService) {
super();
this.userService = userService;
}*/
publicvoidsetUserService(UserServiceuserService) {
this.userService=userService;
}
}
UserService.java
publicclassUserService{
privateGoodsServicegoodsService;
/* public UserService(GoodsService goodsService) {
super();
this.goodsService = goodsService;
}
*/
publicvoidsetGoodsService(GoodsServicegoodsService) {
this.goodsService=goodsService;
}
}
