Question

我需要帮助来设置我的弹簧应用程序。我在访问@Service和@Repository类中的@Autowired字段时遇到空指针异常。但我在@Controller类中得到了适当的价值。我试着调试。在DEBUG模式下，当应用程序启动时，字段userDao和dataSource的值将获取正确的值，但是当我尝试通过遍历实际流程进行调试时，一旦服务器启动，则值为null。这是我的servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
    xmlns:sec="http://www.springframework.org/schema/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:beans="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/security
        http://www.springframework.org/schema/security/spring-security-3.1.xsd">

    <!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->

    <!-- Enables the Spring MVC @Controller programming model -->
    <annotation-driven />

    <!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources directory -->
    <resources mapping="/resources/**" location="/resources/" />

    <!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
    <beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <beans:property name="prefix" value="/WEB-INF/views/" />
        <beans:property name="suffix" value=".jsp" />
    </beans:bean>

    <context:component-scan base-package="com" />

</beans:beans>

这是我的Controller类，它可以很好地处理UserService的自动装配。

@Controller
public class HomeController {

    @Autowired
    private UserService userService;

    public void setUserService(UserService userService) {
        this.userService = userService;
    }
@RequestMapping(value = "/register", method = RequestMethod.POST)
    public ModelAndView register(HttpServletRequest request){
        ModelAndView modelAndView = new ModelAndView();
        String result = userService.createUser(request);
        if(result.equals("SUCCESS"))
        {
            modelAndView.addObject("user",request.getParameter("firstname"));
            modelAndView.setViewName("scramble");
        }
        else
            modelAndView.setViewName("registrationerror");
        return modelAndView;
    }

}

这是我的UserServiceImpl类，其中userDao的autowire给出了NullPointerException。

@Service("UserService")
public class UserServiceImpl implements UserService, UserDetailsService{

    private UserDao userDao;

    public UserDao getUserDao() {
        return userDao;
    }

    @Autowired
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public String createUser(HttpServletRequest request) {
        User user = new User();
        SecurePasswordGenerator secGenerator = new SecurePasswordGenerator();
        String hashedPassword = secGenerator.passwordGeneratorFunction(request.getParameter("password"));
        user.setFirstname(request.getParameter("firstname"));
        user.setLastname(request.getParameter("lastname"));
        user.setEmail(request.getParameter("email"));
        user.setHashedPass(hashedPassword);
        user.setAddress(request.getParameter("address"));
        user.setZipcode(request.getParameter("zipcode"));

        user.setAge(Integer.parseInt(request.getParameter("age")));
        String result = userDao.createUser(user);
        return result;
    }
}

这是我的UserDaoImpl类，其中dataSource的自动装配给出了NullPointerException。

@Repository("UserDao")
public class UserDaoImpl implements UserDao{


    private DataSource dataSource;
    @Autowired
    public void setDataSource(DataSource dataSource) {
       this.dataSource = dataSource;
    }

    protected final Log logger = LogFactory.getLog(getClass());  

    @Override
    public String createUser(User user)
    {
        try {
            String insertUserSQL = "INSERT INTO USER (FIRSTNAME, LASTNAME, EMAIL, PASSKEY, ADDRESS, ZIPCODE, AGE) VALUES (?, ?, ?, ?, ?, ?)";
            JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
            jdbcTemplate.update(insertUserSQL,  
                             new Object[] { user.getFirstname(), user.getLastname(), user.getEmail(),  
                      user.getHashedPass(), user.getAddress(), user.getZipcode(), user.getAge() });
            return "SUCCESS";
        } catch (Exception e) {
            e.printStackTrace();
            return "FAILURE";
        }
    }

}

我也提供了我的root-context.xml，我已经声明了我的身份验证和数据源。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:sec="http://www.springframework.org/schema/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
                        http://www.springframework.org/schema/beans/spring-beans.xsd
                        http://www.springframework.org/schema/security 
                        http://www.springframework.org/schema/security/spring-security-3.1.xsd">

    <!-- Root Context: defines shared resources visible to all other web components -->
    <sec:http auto-config="true" use-expressions="true" access-denied-page="/denied">
        <sec:intercept-url pattern="/home" access="isAnonymous()" />
        <sec:intercept-url pattern="/login" access="isAnonymous()" />
        <sec:intercept-url pattern="/logout" access="isAnonymous()" />   
        <sec:intercept-url pattern="/scramble" access="isAuthenticated()"></sec:intercept-url>      
        <sec:form-login login-page="/login" default-target-url="/home" authentication-failure-url="/error" />
        <sec:logout
            invalidate-session="true"
            delete-cookies="SPRING_SECURITY_REMEMBER_ME_COOKIE"
            logout-success-url="/logout"/>              
    </sec:http>
    <sec:authentication-manager >
        <sec:authentication-provider user-service-ref="userService">
            <sec:password-encoder ref="encoder"/>
        </sec:authentication-provider>  
    </sec:authentication-manager>

    <!-- declare datasource bean -->  
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">  
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />  
        <property name="url" value="jdbc:mysql://localhost:3306/english_words" />  
        <property name="username" value="root" />  
        <property name="password" value="root" />  
    </bean> 

    <bean id="userService" class="com.unscramble.serviceImpl.UserServiceImpl"/>

    <!-- For hashing and salting user passwords -->
    <bean id="encoder" class="org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder"/>

</beans>

以下是我得到的错误。

Aug 16, 2014 10:51:54 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet appServlet threw exception
java.lang.NullPointerException
    at com.unscramble.serviceImpl.UserServiceImpl.createUser(UserServiceImpl.java:43)
    at com.unscramble.controller.HomeController.register(HomeController.java:69)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:213)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:643)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:311)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:116)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:101)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:182)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:323)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:173)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259)
    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:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at

org.apache.coyote.http11.Http11Protocol $ Http11ConnectionHandler.process（Http11Protocol.java:606）在org.apache.tomcat.util.net.JIoEndpoint $ Worker.run（JIoEndpoint.java:489）在java.lang.Thread.run（Thread.java:722）

提前致谢。我使用的是弹簧3.1.0。如果需要任何进一步的信息，请告诉我。

按要求添加弹簧日志。

Aug 17, 2014 11:53:10 AM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Program Files\Java\jdk1.7.0_11\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:/Program Files/Java/jdk1.7.0_11/bin/../jre/bin/server;C:/Program Files/Java/jdk1.7.0_11/bin/../jre/bin;C:/Program Files/Java/jdk1.7.0_11/bin/../jre/lib/amd64;C:\Program Files\Java\jdk1.7.0_11/bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static;C:\Program Files\apache-ant-1.9.4-bin/bin;C:\Program Files (x86)\MySQL\MySQL Utilities 1.3.6\;G:\Android\eclipse;;.
Aug 17, 2014 11:53:10 AM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:Unscramble' did not find a matching property.
Aug 17, 2014 11:53:10 AM org.apache.coyote.http11.Http11Protocol init
INFO: Initializing Coyote HTTP/1.1 on http-8080
Aug 17, 2014 11:53:10 AM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 609 ms
Aug 17, 2014 11:53:10 AM org.apache.catalina.core.StandardService start
INFO: Starting service Catalina
Aug 17, 2014 11:53:10 AM org.apache.catalina.core.StandardEngine start
INFO: Starting Servlet Engine: Apache Tomcat/6.0.37
Aug 17, 2014 11:53:11 AM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring root WebApplicationContext
INFO : org.springframework.web.context.ContextLoader - Root WebApplicationContext: initialization started
INFO : org.springframework.web.context.support.XmlWebApplicationContext - Refreshing Root WebApplicationContext: startup date [Sun Aug 17 11:53:11 IST 2014]; root of context hierarchy
INFO : org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loading XML bean definitions from ServletContext resource [/WEB-INF/spring/root-context.xml]
INFO : org.springframework.beans.factory.support.DefaultListableBeanFactory - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@8bc1115: defining beans [org.springframework.security.filterChains,org.springframework.security.filterChainProxy,org.springframework.security.web.PortMapperImpl#0,org.springframework.security.config.authentication.AuthenticationManagerFactoryBean#0,org.springframework.security.authentication.ProviderManager#0,org.springframework.security.web.context.HttpSessionSecurityContextRepository#0,org.springframework.security.web.authentication.session.SessionFixationProtectionStrategy#0,org.springframework.security.web.savedrequest.HttpSessionRequestCache#0,org.springframework.security.web.access.expression.DefaultWebSecurityExpressionHandler#0,org.springframework.security.access.vote.AffirmativeBased#0,org.springframework.security.web.access.intercept.FilterSecurityInterceptor#0,org.springframework.security.web.access.DefaultWebInvocationPrivilegeEvaluator#0,org.springframework.security.authentication.AnonymousAuthenticationProvider#0,org.springframework.security.web.authentication.www.BasicAuthenticationEntryPoint#0,org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter#0,org.springframework.security.userDetailsServiceFactory,org.springframework.security.web.DefaultSecurityFilterChain#0,org.springframework.security.authentication.dao.DaoAuthenticationProvider#0,org.springframework.security.authentication.DefaultAuthenticationEventPublisher#0,org.springframework.security.authenticationManager,userService,encoder]; root of factory hierarchy
INFO : org.springframework.web.context.ContextLoader - Root WebApplicationContext: initialization completed in 993 ms
Aug 17, 2014 11:53:12 AM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring FrameworkServlet 'appServlet'
INFO : org.springframework.web.servlet.DispatcherServlet - FrameworkServlet 'appServlet': initialization started
INFO : org.springframework.web.context.support.XmlWebApplicationContext - Refreshing WebApplicationContext for namespace 'appServlet-servlet': startup date [Sun Aug 17 11:53:12 IST 2014]; parent: Root WebApplicationContext
INFO : org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loading XML bean definitions from ServletContext resource [/WEB-INF/spring/appServlet/servlet-context.xml]
INFO : org.springframework.context.annotation.ClassPathBeanDefinitionScanner - JSR-330 'javax.inject.Named' annotation found and supported for component scanning
INFO : org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor - JSR-330 'javax.inject.Inject' annotation found and supported for autowiring
INFO : org.springframework.beans.factory.support.DefaultListableBeanFactory - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@43a0ddf: defining beans [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#0,org.springframework.format.support.FormattingConversionServiceFactoryBean#0,org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#0,org.springframework.web.servlet.handler.MappedInterceptor#0,org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver#0,org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver#0,org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver#0,org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,org.springframework.web.servlet.resource.ResourceHttpRequestHandler#0,org.springframework.web.servlet.handler.SimpleUrlHandlerMapping#0,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.web.servlet.view.InternalResourceViewResolver#0,homeController,loginController,UserDao,UserService,dataSource,userDao,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; parent: org.springframework.beans.factory.support.DefaultListableBeanFactory@8bc1115
INFO : org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped "{[/register],methods=[POST],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public org.springframework.web.servlet.ModelAndView com.unscramble.controller.HomeController.register(javax.servlet.http.HttpServletRequest)
INFO : org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped "{[/home],methods=[GET],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public org.springframework.web.servlet.ModelAndView com.unscramble.controller.HomeController.home()
INFO : org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped "{[/unscramble],methods=[POST],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public org.springframework.web.servlet.ModelAndView com.unscramble.controller.HomeController.unscramble(java.lang.String)
INFO : org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped "{[/signup],methods=[GET],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public org.springframework.web.servlet.ModelAndView com.unscramble.controller.HomeController.signup()
INFO : org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping - Mapped "{[/login],methods=[POST],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public org.springframework.web.servlet.ModelAndView com.unscramble.controller.LoginController.login(java.lang.String,java.lang.String,java.lang.String)
INFO : org.springframework.web.servlet.handler.SimpleUrlHandlerMapping - Mapped URL path [/resources/**] onto handler 'org.springframework.web.servlet.resource.ResourceHttpRequestHandler#0'
INFO : org.springframework.web.servlet.DispatcherServlet - FrameworkServlet 'appServlet': initialization completed in 1473 ms
Aug 17, 2014 11:53:13 AM org.apache.coyote.http11.Http11Protocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
Aug 17, 2014 11:53:13 AM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
Aug 17, 2014 11:53:13 AM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/22  config=null
Aug 17, 2014 11:53:13 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 3305 ms
Aug 17, 2014 11:54:08 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet appServlet threw exception
java.lang.NullPointerException
    at com.unscramble.serviceImpl.UserServiceImpl.createUser(UserServiceImpl.java:45)
    at com.unscramble.controller.HomeController.register(HomeController.java:69)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:213)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)

我还尝试进行一些更改，以更具体的方式显示我的错误。我在setUserDao方法中添加了一个system.print语句，并且在UserServiceImpl.java中的userDao.createUser行之前。所以我的UserServiceImpl看起来像

@Autowired
    @Qualifier("UserDao")
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
        System.out.println("The userDao is set and the value is : " + userDao);
    }

    @Override
    public String createUser(HttpServletRequest request) {

        <more code here>

        user.setAge(Integer.parseInt(request.getParameter("age")));
        System.out.println("The userDao in createUser has value : " + userDao);
        String result = userDao.createUser(user);
        return result;
    }

正如我之前在服务器启动时所述，它会打印userDao值。但是一旦服务器启动并且我尝试访问页面。在主流程中，userDao打印为null。您可以查看我粘贴的以下日志。从底部检查第一行，从底部检查第三行或第四行以查看差异。

    <few logs here> 
The userDao is set and the value is : com.unscramble.daoImpl.UserDaoImpl@2665d910
INFO : org.springframework.web.servlet.DispatcherServlet - FrameworkServlet 'appServlet': initialization completed in 1427 ms
Aug 17, 2014 12:35:49 PM org.apache.coyote.http11.Http11Protocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
Aug 17, 2014 12:35:49 PM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
Aug 17, 2014 12:35:49 PM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/26  config=null
Aug 17, 2014 12:35:49 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 3201 ms
The userDao in createUser has value : null
Aug 17, 2014 12:36:45 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet appServlet threw exception
java.lang.NullPointerException
    at com.unscramble.serviceImpl.UserServiceImpl.createUser(UserServiceImpl.java:47)

Answer 1

在你的代码中我唯一看起来很奇怪的是你在setter函数之前指定了getter函数请在setter函数之后声明getter并检查它是否正常工作。有些时候由于服务器问题，清理服务器并重新启动它。

Spring：@Autowired不在@Service，@ Repository Class中工作但在@Controller类中工作

1 个答案: