关于ssh项目的action中@Autowired service和pojo的顺序的疑问

Question

原来代码中写的是
[code="java"]
@Autowired
private UserService userService;
private User user;
[/code]
没有问题。
今天手欠改了下顺序
[code="java"]
@Autowired
private User user;
private UserService userService;
[/code]
然后就报错：
[code="java"]
严重: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'usermanagementAction': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.wangy.demo.models.User com.wangy.demo.actions.usermanagement.UsermanagementAction.user; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.wangy.demo.models.User] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:287)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:384)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:283)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:111)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4791)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5285)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:618)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1100)
at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1618)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.wangy.demo.models.User com.wangy.demo.actions.usermanagement.UsermanagementAction.user; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.wangy.demo.models.User] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:506)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:284)
... 27 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.wangy.demo.models.User] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:924)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:793)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:707)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:478)
... 29 more
[/code]

估计跟UserService有些关系，但是其中只有用到UserDAO
[code="java"]
@Service("userService")
public class UserService {
@Autowired
private UserDAO userDAO;

public UserDAO getUserDAO() {
    return userDAO;
}

public void setUserDAO(UserDAO userDAO) {
    this.userDAO = userDAO;
}

/**
 * 
 * @param username
 * @param password
 * @return
 */
public User login(String username, String password){
    List userList = userDAO.findByUsernameAndPassword(username, password);
    if(userList != null && !userList.isEmpty()){
        User user = (User)userList.get(0);
        return user;
    }
    return null;
}

}
[/code]

spring配置的为default-autowire="byName"
在网上找了一直没找到原因，请各位帮忙解惑，谢谢

Answer 1

@Autowired

private UserService userService;
表示自动装配一个userServicebean

@Autowired

private User user;
那么spring会去找user这个bean，结果肯定找不到
[color=red]Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.wangy.demo.models.User] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} [/color]

@Autowired 该注解是作用在field上面的