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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  0   2    java/ spring/ dependency-injection

问题描述

I have this structure: 我有这个结构：

An interface IProjectService and this is implemented by ProjectServiceImpl. 接口IProjectService，由ProjectServiceImpl实现。

Now I have a controller in which I want to use the Dependency Injection: 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;
    }
}

In my applicationContext.xml I have these lines of code: 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>

But if I run my application I get an error (NullPointerException) in my MyDIController in this line of code: 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);

The problem is, that 问题是 

this.projectServiceImpl

is null and so it seems that the Dependency Injection does not work. 为null，因此似乎依赖项注入无效。

What's wrong here, does anyone know? 这是怎么了，有人知道吗？

Best Regards Tim. 最好的问候蒂姆。

Update: 更新：

Full Error Trace: 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: 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: 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: 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

You haven;t injected property projectServiceImpl for MyDIController 您的避风港;吨注入属性projectServiceImpl为MyDIController

Conf. Conf。 should be like 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>

in web.xml 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

You have a few options. 您有几种选择。

  1. Declare an XML Bean for your controller and set the property for your service in that. 为您的控制器声明一个XML Bean，并在其中设置服务的属性。
  2. Depending on your version of Spring, use Spring's Annotation/Autowiring support. 根据您的Spring版本，使用Spring的Annotation / Autowiring支持。

If you choose number 2, be sure to include <context:component-scan base-package="com.your.package"/> in your xml configuration and mark your controller class with @Controller and @Autowired for your projectService property. 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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