Spring IOC深入学习

接上篇<<模拟Spring实现>>，本节来学习IOC。

在上篇的基础上，保留model，DAO，Service，我们加入Spring依赖，这里我用的Spring版本是2.6.5。spring.jar，commons-logging.jar。

1.beans.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-2.5.xsd">

  <bean id="u" class="com.yuwl.dao.impl.UserDAOImpl">
  </bean>
	
  <bean id="userService" class="com.yuwl.service.UserService">
  	<property name="userDAO" ref="u" />
  </bean>

</beans>

2.测试

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.yuwl.model.User;

//Dependency Injection
//Inverse of Control
public class UserServiceTest {

	@Test
	public void testAdd() throws Exception {
		ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
		UserService service = (UserService)ctx.getBean("userService");
		
		User u = new User();
		u.setUsername("yuwl");
		u.setPassword("123456");
		service.add(u);
	}

}

结果，执行成功：user saved!

说明：这里为什么使用ApplicationContext，而不用BeanFactory，根据官方文档，BeanFactory是基类，子类ApplicationContext比它做了更好的扩展，功能更强大，因此官方推荐使用ApplicationContext。

3.理解IOC

理解DI：

直接理解IOC，不太好说，先来说DI—Dependency Injection，依赖注入。

看配置文件beans.xml，userService依赖Spring容器注入userDAO，从而得到userDAO实例。

再看另一方面，userService也是通过Spring容器注入com.bjsxt.service.UserService，我们才能不用new而获得其实例，userDAO也是一样。

理解IOC：

依赖注入搞明白了，再来看IOC—Inverse of Control，控制反转，以前写程序都是我们自己new的service，自己new的dao，但是现在交给Spring容器来完成了，配下配置文件，简单又灵活就搞定了，是不是把这控制权交给了Spring，这就是控制反转。把控制权由我们人为控制交给Spring来控制。

4.注入类型

Spring提供的注入类型有三种：

a.setter(最常用)

b.构造方法(不常用)

c.接口或属性(基本不用)

我们一般用的最多的就是setter，其它两种可以不用掌握。

5.<bean中的scope属性

a.singleton单例

b.proptotype 每次创建新的对象

不写默认为singleton单例，一般配置Action的bean时，设置为proptotype。

6.自动装配

a.byName—根据bean name来自动选择

b.byType—根据bean class来自动选择

c.如果所有的bean都用同一种，可以使用beans的属性：default-autowire

byName:

<?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-2.5.xsd"
          >
  <!-- byName -->
  <bean name="userDAO" class="com.yuwl.dao.impl.UserDAOImpl">
  	<property name="daoId" value="1"></property>
  </bean>
  
  <bean name="userDAO2" class="com.yuwl.dao.impl.UserDAOImpl">
  	<property name="daoId" value="2"></property>
  </bean>
	
  <bean id="userService" class="com.yuwl.service.UserService" autowire="byName">
  </bean>

</beans>

byType:

<?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-2.5.xsd"
          >
  <!-- byType -->
  <bean name="userDAO" class="com.yuwl.dao.impl.UserDAOImpl">
  	<property name="daoId" value="1"></property>
  </bean>
  <!--  
  <bean name="userDAO2" class="com.yuwl.dao.impl.UserDAOImpl">
  	<property name="daoId" value="2"></property>
  </bean>
  -->
  <bean id="userService" class="com.yuwl.service.UserService" autowire="byType">
  </bean>

</beans>

7.Annotation第一步

修改xml文件，加入<context:annotation-config />

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">
	
	<context:annotation-config />
	
  	<bean id="u" class="com.yuwl.dao.impl.UserDAOImpl">
  	</bean>
  	
  	<bean id="u2" class="com.yuwl.dao.impl.UserDAOImpl">
  	</bean>
	
	<bean id="userService" class="com.yuwl.service.UserService" >
	</bean>

</beans>

8.@Autowired

a.默认按类型byType

b.如果想用byName，使用@Qulifier

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

public class UserService {
	
	private UserDAO userDAO;  
	
	public void init() {
		System.out.println("init");
	}
	
	public void add(User user) {
		userDAO.save(user);
	}
	public UserDAO getUserDAO() {
		return userDAO;
	}
	
	@Autowired
	public void setUserDAO(@Qualifier("u") UserDAO userDAO) {
		this.userDAO = userDAO;
	}
	
	public void destroy() {
		System.out.println("destroy");
	}
}

9.@Resource（重要）

a.加入：j2ee/common-annotations.jar

b.默认按名称byName，名称找不到，按类型byType

c.可以指定特定名称

d.推荐使用

import javax.annotation.Resource;
import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

public class UserService {
	
	private UserDAO userDAO;  
	
	public void init() {
		System.out.println("init");
	}
	
	public void add(User user) {
		userDAO.save(user);
	}
	public UserDAO getUserDAO() {
		return userDAO;
	}
	
	@Resource
	public void setUserDAO( UserDAO userDAO) {
		this.userDAO = userDAO;
	}
	
	public void destroy() {
		System.out.println("destroy");
	}
}

10.@Component @Service @Controller @Repository

a.初始化的名字默认为类名首字母小写

b.可以指定初始化bean的名字

beans.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"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">
	<context:annotation-config />
	<context:component-scan base-package="com.yuwl"/>
 
</beans>

Spring容器按包结构base-package="com.yuwl"来搜索要初始化的bean

UserDAOImpl:

import org.springframework.stereotype.Component;
import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

@Component("u") 
public class UserDAOImpl implements UserDAO {

	public void save(User user) {
		//Hibernate or Jdbc add
		System.out.println("user saved!");
	}

}

UserService:

import javax.annotation.Resource;
import org.springframework.stereotype.Component;
import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

@Component("userService")
public class UserService {
	
	private UserDAO userDAO;  
	
	public void init() {
		System.out.println("init");
	}
	
	public void add(User user) {
		userDAO.save(user);
	}
	public UserDAO getUserDAO() {
		return userDAO;
	}
	
	@Resource(name="u")
	public void setUserDAO( UserDAO userDAO) {
		this.userDAO = userDAO;
	}
	
	public void destroy() {
		System.out.println("destroy");
	}
}

Spring IOC最主要的核心内容就学到这，下面将深入AOP的学习。

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