Spring 实例化 bean 的形式
- Set注入
- 结构器注入
- 动态工厂注入
- 实例化工厂注入
案例实操
Set注入
xml配置（同时spring也提供了对于根本数据类型的set注入形式）
<?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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="userDao" class="com.xxx.demo.UserDao"></bean> <!-- setter注入 --> <bean id="userService" class="com.xxx.demo.UserService"> <!--ref是对于内部bean对象援用，与被援用的bean对象的id保持一致--> <property name="userDao" ref="userDao"></property> </bean></beans> UserDao.java
public class UserDao { public String userLogin() { return "我是UserDao中的userLogin()的办法"; }} UserService.java
public class UserService { //肯定要提供属性的setter办法 private UserDao userDao; public void userlogin() { String res=userDao.userLogin(); System.out.println(res); } public void setUserDao(UserDao userDao) { this.userDao = userDao; }} App.java
import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class App { public static void main(String[] args) { ApplicationContext applicationContext=new ClassPathXmlApplicationContext("spring-config.xml"); UserService userService=applicationContext.getBean("userService", UserService.class); userService.userlogin(); }} 结构器注入
xml配置（也提供对于根本数据类型、字符串等值的注入）
<?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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="userDao" class="com.xxx.demo.UserDao"></bean> <!-- 结构器注入 --> <bean id="userServiceV2" class="com.xxx.demo.UserServiceV2"> <constructor-arg index="0" ref="userDao"></constructor-arg> <constructor-arg index="1" value="印度三哥"></constructor-arg> </bean></beans> 结构器注入有三种模式：
index属性为参数程序，如果只有一个参数index能够不设置。
name属性依据结构器中属性的名字。
type属性，是依据结构器中属性的类型来匹配的。如果雷同类型属性不惟一，注入的属性依照程序注入进来。
UserServiceV2.java类提供构造函数
/** * 实现结构器注入 * @author Best Liu * */public class UserServiceV2 { private UserDao userDao; private String name; public void userlogin() { String res=userDao.userLogin(); System.out.println(res); System.out.println(name); } public UserServiceV2(UserDao userDao,String name) { super(); this.userDao = userDao; this.name = name; }} 动态工厂注入
xml配置
<?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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 动态工厂注入 --> <bean id="userDao01" class="com.xxx.demo.StaticFactory" factory-method="createuserDao"></bean> <bean id="userService01" class="com.xxx.demo.UserService"> <property name="userDao" ref="userDao01"></property> </bean></beans> StaticFactory.java
public class StaticFactory { public static UserDao createuserDao(){ return new UserDao(); }} UserService.java
public class UserService { private UserDao userDao; public void userlogin() { String res=userDao.userLogin(); System.out.println(res); } public void setUserDao(UserDao userDao) { this.userDao = userDao; }} tips:动态工厂注入就是IoC动态工厂和DI的setter注入，将须要注入的属性对象利用动态工厂创立进去.
2.4 实例化工厂
xml配置
<?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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 实例化工厂 --> <bean id="instanceFactory" class="com.xxx.demo.InstanceFactory"></bean> <bean id="userDao3" factory-bean="instanceFactory" factory-method="createUserDao"></bean> <bean id="userService02" class="com.xxx.demo.UserService"> <property name="userDao" ref="userDao3"></property> </bean></beans> InstanceFactory.java
public class InstanceFactory { public UserDao createUserDao(){ return new UserDao(); }} tips:重点把握set，结构器注入，工厂形式理解即可，理论开发中根本应用set形式注入bean。
扩大
循环依赖的问题的产生
Bean通过结构器注入，之间彼此相互依赖对方导致bean无奈实例化。
注入的抉择：开发我的项目中set形式注入首选
应用结构注入能够在构建对象的同时一并实现依赖关系的建设，对象一建设则所有的所有也就筹备好了，但如果要建设的对象关系很多，应用结构注入会在构建函数上留下一长串的参数，且不易记忆，这时应用Set注入会是个不错的抉择。
应用Set注入能够有明确的名称，能够理解注入的对象会是什么，像setxxx()这样的名称比记忆Constructor上某个参数的地位代表某个对象更好。
xml配置
<?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/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="goodsService" class="com.xxx.demo.GoodsService"> <!-- <constructor-arg index="0" ref="userService"></constructor-arg> --> <property name="userService" ref="userService"></property> </bean> <bean id="userService" class="com.xxx.demo.UserService"> <!-- <constructor-arg index="0" ref="goodsService"></constructor-arg> --> <property name="goodsService" ref="goodsService"></property> </bean></beans> GoodsService.java
public class GoodsService { private UserService userService; /*public GoodsService(UserService userService) { super(); this.userService = userService; }*/ public void setUserService(UserService userService) { this.userService = userService; }} UserService.java
public class UserService { private GoodsService goodsService;/* public UserService(GoodsService goodsService) { super(); this.goodsService = goodsService; }*/ public void setGoodsService(GoodsService goodsService) { this.goodsService = goodsService; } }