Spring 自动装配AutoWire

引用:

在xml配置文件中，autowire有5种类型，可以在<bean/>元素中使用autowire属性指定



模式 说明

no 不使用自动装配，必须通过ref元素指定依赖，默认设置。

byName 根据属性名自动装配。此选项将检查容器并根据名字查找与

属性完全一致的bean，并将其与属性自动装配。

byType 如果容器中存在一个与指定属性类型相同的bean，那么将与

该属性自动装配；如果存在多个该类型bean，那么抛出异

常，并指出不能使用byType方式进行自动装配；如果没有找

到相匹配的bean，则什么事都不发生，也可以通过设置

dependency-check="objects"让Spring抛出异常。

constructor 与byType方式类似，不同之处在于它应用于构造器参数。如

果容器中没有找到与构造器参数类型一致的bean，那么抛出

异常。

autodetect 通过bean类的自省机制（introspection）来决定是使用

constructor还是byType方式进行自动装配。如果发现默认的

构造器，那么将使用byType方式。

可以设置bean使自动装配失效：

采用xml格式配置bean时，将<bean/>元素的autowire-candidate属性设置为false，这样容器在查找自动装配对象时，将不考虑该bean，即它不会被考虑作为其它bean自动装配的候选者，但是该bean本身还是可以使用自动装配来注入其它bean的。

测试:

test文件:

package com.bjsxt.dao;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bjsxt.model.User;
import com.bjsxt.service.UserService;

 class Test {
	public static void main(String[] args){
   ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
		
		
		UserService service = (UserService)ctx.getBean("userService");
		
		System.out.println(service.getUserDAO());
	}

}

首先采用 "byName" 的方式.配置文件如下:

<?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 name="userDAO2" class="com.bjsxt.dao.impl.UserDAOImpl">
  	<property name="daoId" value="1"></property>
  </bean>
  
  <bean name="userDAO" class="com.bjsxt.dao.impl.UserDAOImpl">
  	<property name="daoId" value="2"></property>
  </bean>
	
  <bean id="userService" class="com.bjsxt.service.UserService" scope="prototype" autowire="byName">
  
   <!--  autowire="byType"
   <property name="userDAO" ref="userDAO" />-->
  </bean>
  

</beans>

因为service中存在 名为userDAO的成员:

package com.bjsxt.service;
import com.bjsxt.dao.UserDAO;
import com.bjsxt.model.User;

public class UserService {
	
	private UserDAO userDAO;  
	public void add(User user) {
		userDAO.save(user);
	}
	public UserDAO getUserDAO() {
		return userDAO;
	}
	public void setUserDAO(UserDAO userDAO) {
		this.userDAO = userDAO;
	}
	

}

所以采用byName方式匹配时, 选中的name为 userDAO的bean.

Test输出如下:

<span style="background-color: rgb(255, 255, 255);"><span style="color:#ff6666;">INFO: Loading XML bean definitions from class path resource [beans.xml]
五月 26, 2014 10:42:23 上午 org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.context.support.ClassPathXmlApplicationContext@34b172ef]: org.springframework.beans.factory.support.DefaultListableBeanFactory@2ea8bf33
五月 26, 2014 10:42:23 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@2ea8bf33: defining beans [userDAO2,userDAO,userService]; root of factory hierarchy</span></span><span style="color:#232323;">
daoId=2</span>

换成"byType"

因为存在两个类型相同的bean. 程序报错

五月 26, 2014 10:45:23 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908: display name [org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908]; startup date [Mon May 26 10:45:23 CST 2014]; root of context hierarchy
五月 26, 2014 10:45:23 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [beans.xml]
五月 26, 2014 10:45:24 上午 org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908]: org.springframework.beans.factory.support.DefaultListableBeanFactory@73354684
五月 26, 2014 10:45:24 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@73354684: defining beans [userDAO2,userDAO,userService]; root of factory hierarchy
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService' defined in class path resource [beans.xml]: Unsatisfied dependency expressed through bean property 'userDAO': : No unique bean of type [com.bjsxt.dao.UserDAO] is defined: expected single matching bean but found 2: [userDAO2, userDAO]; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.bjsxt.dao.UserDAO] is defined: expected single matching bean but found 2: [userDAO2, userDAO]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1091)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:982)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
	at java.security.AccessController.doPrivileged(Native Method)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:283)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:880)
	at com.bjsxt.dao.Test.main(Test.java:15)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.bjsxt.dao.UserDAO] is defined: expected single matching bean but found 2: [userDAO2, userDAO]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:621)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1076)
	... 10 more

在此基础上,如果将第二个bean的autowire-candidate 属性设为false:

<?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 name="userDAO2" class="com.bjsxt.dao.impl.UserDAOImpl">
  	<property name="daoId" value="1"></property>
  </bean>
  
  <bean name="userDAO" class="com.bjsxt.dao.impl.UserDAOImpl" autowire-candidate="false">
  	<property name="daoId" value="2"></property>
  </bean>
	
  <bean id="userService" class="com.bjsxt.service.UserService" scope="prototype" autowire="byType">
  
   <!--  autowire="byType"
   <property name="userDAO" ref="userDAO" />-->
  </bean>
  

</beans>

则在匹配时只有第一个bean符合条件, 不发生冲突, 正常输出结果:

<span style="color:#ff6666;">五月 26, 2014 10:46:46 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908: display name [org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908]; startup date [Mon May 26 10:46:46 CST 2014]; root of context hierarchy
五月 26, 2014 10:46:46 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [beans.xml]
五月 26, 2014 10:46:46 上午 org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.context.support.ClassPathXmlApplicationContext@2c4a1908]: org.springframework.beans.factory.support.DefaultListableBeanFactory@73354684
五月 26, 2014 10:46:46 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@73354684: defining beans [userDAO2,userDAO,userService]; root of factory hierarchy</span><span style="color:#232323;">
daoId=1</span>