Spring2.5学习3.3_@Autowire注解实现手动装配

@Autowired默认按类型装配，假设我在personDao 字段上加了@Autowired注解，那么就会默认取personDao 字段的类型在Spring容器中寻找与这个类型匹配的bean,寻找到相应的bean之后就会把这个bean注入到该字段上来。

默认情况下必需要求依赖对象必须存在。假设要同意null 值，能够设置它的required属性为false，如：@Autowired(required=false) 。假设我们想使用名称装配能够结合@Qualifier注解进行使用，例如以下： 

@Autowired() @Qualifier("personDao")     
private PersonDao personDao ;

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/>
          
          <bean id="personDao" class="xjj.dao.impl.PersonDaoBean"></bean>
          <bean id="personService" class="xjj.service.impl.PersonServiceBean" ></bean>
</beans>

首先看看默认按类型装配：PersonServiceBean.java 

package xjj.service.impl;

import org.springframework.beans.factory.annotation.Autowired;

import xjj.dao.PersonDao;
import xjj.service.PersonService;

public class PersonServiceBean implements PersonService {
	@Autowired
	private PersonDao personDao;
	
	public void setPersonDao(PersonDao personDao) {
		this.personDao = personDao;
	}

	public void save(){
		personDao.add();
	}
}
在測试类SpringTest2.java中，我们调用personservice的save方法，假设装配失败，会出现空指针异常

如今我们看一下測试结果：注入成功

接下来我们验证一下，结合@Qualifier注解按名称装配

@Autowired @Qualifier("personDaoxxxx")
	private PersonDao personDao;
beans.xml中bean的名称没有与注入名称一致的bean，就会发生异常 

<bean id="personDao" class="xjj.dao.impl.PersonDaoBean"></bean>
<bean id="personService" class="xjj.service.impl.PersonServiceBean" ></bean>

结果： 

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'personService': Autowiring of fields failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private xjj.dao.PersonDao xjj.service.impl.PersonServiceBean.personDao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [xjj.dao.PersonDao] is defined: Unsatisfied dependency of type [interface xjj.dao.PersonDao]: expected at least 1 matching bean
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessAfterInstantiation(AutowiredAnnotationBeanPostProcessor.java:243)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:959)
	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$1.getObject(AbstractBeanFactory.java:264)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
	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.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
	at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
	at junit.test.SpringTest2.instanceSpring(SpringTest2.java:13)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private xjj.dao.PersonDao xjj.service.impl.PersonServiceBean.personDao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [xjj.dao.PersonDao] is defined: Unsatisfied dependency of type [interface xjj.dao.PersonDao]: expected at least 1 matching bean
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:435)
	at org.springframework.beans.factory.annotation.InjectionMetadata.injectFields(InjectionMetadata.java:105)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessAfterInstantiation(AutowiredAnnotationBeanPostProcessor.java:240)
	... 39 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [xjj.dao.PersonDao] is defined: Unsatisfied dependency of type [interface xjj.dao.PersonDao]: expected at least 1 matching bean
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:613)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:412)
	... 41 more

假设我们把两个bean名称改成一致，就会注入成功 

<bean id="personDaoxxxx" class="xjj.dao.impl.PersonDaoBean"></bean>
<bean id="personService" class="xjj.service.impl.PersonServiceBean" ></bean>
结果：



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原文地址：https://www.cnblogs.com/zfyouxi/p/5137347.html