使用@Autowired的Spring Injection

Question

我在嘗試使用Spring @Autowired注釋運行程序時遇到了@Autowired 。 為了向您解釋我要做什么，我有一個主控制器類MainController ，該類始終使用其他兩個類（ SquadraController類和UserController類）來完成一些工作。

相反，實例化這些類的任何時候，我需要他們，我決定將它們聲明與實例變量@Autowired注解，並呼吁他們任何時候，我需要他們。

因此，我的實例變量帶有@Autowired批注，並在上下文xml文件中聲明了bean，但是出現以下錯誤，但無法擺脫：

20/03/2015 15:10:00 - WARN  - (AbstractApplicationContext.java:487) - Exception encountered during context initialization - cancelling refresh attempt
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private org.fabrizio.fantavalcanneto.controller.UserController org.fabrizio.fantavalcanneto.controller.MainController.userController; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.fabrizio.fantavalcanneto.controller.UserController] 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:334)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1204)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:538)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:629)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:677)
    at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:548)
    at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
    at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    at javax.servlet.GenericServlet.init(GenericServlet.java:158)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1284)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1197)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1087)

這是我的MainController類（引發錯誤的代碼段）：

@Controller
public class MainController {

    private static final Logger logger = LoggerFactory.getLogger(MainController.class);

    @Autowired
    private UserController userController;

    @Autowired
    private SquadraController squadraController;

這是我聲明我的bean的xml文件（我也嘗試聲明MainController bean而沒有將實例變量聲明為屬性）：

<?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:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="

http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.0.xsd

http://www.springframework.org/schema/context 
http://www.springframework.org/schema/context/spring-context-4.0.xsd">


 <context:component-scan base-package="org.fabrizio.fantavalcanneto.controller" />

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/views/" />
        <property name="suffix" value=".jsp" />
    </bean>

 <bean 
class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>

 <bean id="userController" class="org.fabrizio.fantavalcanneto.controller.UserController" >
 </bean>

 <bean id="mainController" class="org.fabrizio.fantavalcanneto.controller.MainController">
 <property name="userController" value="userController"></property>
 <property name="squadraController" value="squadraController"></property>
 </bean>

 <bean id="squadraController" class="org.fabrizio.fantavalcanneto.controller.SquadraController">
 </bean>
</beans>

UserController和SquadraController沒有實例變量。

Answer 1

如果您正在進行上下文組件掃描，則無需在配置文件中定義Bean，類似的方法將起作用。 您需要做的是在相關類上使用@Controller注釋：

    <context:component-scan base-package="org.fabrizio.fantavalcanneto.controller" />
    // for default converters etc add this aswell 
    <mvc:annotation-driven/>

只要檢查您是否有正確的基本包裝/打字錯誤