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Spring IoC-依赖注入-> NullPointerException

[英]Spring IoC - Dependency Injection -> NullPointerException

 原文  2010-12-09 09:45:15  4   2    java/ spring/ dependency-injection

问题描述

我有这个结构：

接口IProjectService，由ProjectServiceImpl实现。

现在，我有一个要在其中使用依赖注入的控制器： 

@Controller
@RequestMapping(value="/testFolder")
public class MyDIController {
    ...
    private IProjectService projectServiceImpl;

    public void setProjectServiceImpl(IProjectService projectServiceImpl) {
        this.projectServiceImpl= projectServiceImpl;
    }
    ...
    @RequestMapping(value="/project", method=RequestMethod.GET)
    public @ResponseBody Project getProject() {
        Project project = this.projectServiceImpl.getProject(12); // line 37! (id 12 is a test case, it does exist, here is he error: this.projectServiceImpl = null)
        return project;
    }
}

在我的applicationContext.xml中，有以下几行代码： 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
    <bean id="projectServiceImpl" class="com.mydomain.project.service.impl.ProjectServiceImpl" />
    <bean id="projectService" class="com.mydomain.project.service.IProjectService">
        <property name="projectServiceImpl">
            <ref local="projectServiceImpl"/>
        </property>
    </bean>
</beans>

但是，如果我运行我的应用程序，则在以下代码行中的MyDIController中会出现错误（NullPointerException）： 

... = this.projectServiceImpl.getProject(12);

问题是 

this.projectServiceImpl

为null，因此似乎依赖项注入无效。

这是怎么了，有人知道吗？

最好的问候蒂姆。

更新：

完整错误跟踪： 

09.12.2010 11:16:53 org.apache.catalina.core.ApplicationDispatcher invoke
SCHWERWIEGEND: Servlet.service() for servlet project threw exception
java.lang.NullPointerException
    at com.mydomain.project.controller.MyDIController.getAllProjects(MyDIController.java:37)
    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.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
    at org.tuckey.web.filters.urlrewrite.NormalRewrittenUrl.doRewrite(NormalRewrittenUrl.java:195)
    at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:159)
    at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:141)
    at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:90)
    at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:417)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:619)
09.12.2010 11:16:53 org.apache.catalina.core.StandardWrapperValve invoke
SCHWERWIEGEND: Servlet.service() for servlet default threw exception
java.lang.NullPointerException
    at com.mydomain.project.controller.MyDIController.getProject(MyDIController.java:37)
    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.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
    at org.tuckey.web.filters.urlrewrite.NormalRewrittenUrl.doRewrite(NormalRewrittenUrl.java:195)
    at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:159)
    at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:141)
    at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:90)
    at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:417)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:619)

`

applicationContext.xml： 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
    <bean id="projectService" class="com.mydomain.project.service.impl.ProjectServiceImpl" />

    <bean id="myDIController" class="com.mydomain.project.controller.MyDIController">
        <property name="projectServiceImpl">
            <ref local="projectService"/>
        </property>
    </bean>
</beans>

web.xml： 

    <servlet>
    <servlet-name>project</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring/app-config.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

app-config.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-3.0.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!-- Scans the classpath of this application for @Components to deploy as beans -->
    <context:component-scan base-package="com.mydomain.project" />

    <!-- Application Message Bundle -->
    <bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
        <property name="basename" value="/WEB-INF/messages/messages" />
        <property name="cacheSeconds" value="0" />
    </bean>

    <!-- Configures Spring MVC -->
    <import resource="mvc-config.xml" />
</beans>

2 个解决方案

解决方案1
 5 已采纳  2010-12-09 09:49:16

您的避风港;吨注入属性projectServiceImpl为MyDIController

Conf。 应该像 

<bean id="projectService" class="com.mydomain.project.service.impl.ProjectServiceImpl" />

<bean id="myDIController " class="com.mydomain.project.service.MyDIController">
        <property name="projectServiceImpl">
            <ref local="projectService"/>
        </property>
</bean>

在web.xml中 

<web-app>
     <context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>
                /WEB-INF/application-context.xml                     
            </param-value>
        </context-param>
.
.
.
.
<servlet>
.
.
.

解决方案2
 2  2010-12-09 09:54:23

您有几种选择。

  1. 为您的控制器声明一个XML Bean，并在其中设置服务的属性。
  2. 根据您的Spring版本，使用Spring的Annotation / Autowiring支持。

如果选择数字2，请确保在xml配置中包含<context:component-scan base-package="com.your.package"/> ，并为projectService属性的@Controller和@Autowired标记控制器类。

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