Spring MVC 项目中的空指针异常

Posted 2023-02-27

【中文标题】Spring MVC 项目中的空指针异常

【英文标题】：Null Pointer Exception in Spring MVC Project

【发布时间】：2020-02-03 02:49:50

【问题描述】：

我正在创建一个包含教授字段的表单，这些字段是 id (long)、nome(string)、username (string)、email(string) 和 curso_coord(curso)，因为 curso 是类课程的参考变量。

在表单中，输入用户名、姓名和电子邮件字段供用户填写，如果他/她是该课程的协调员，则该课程是用户选择课程的选择，如果不是，则为 -1

我尝试使用 curso.get(0).getId() 来解决问题，但还不够

@Controller
@RequestMapping(value =  "/professor" )
public class ProfessorController 
    @Autowired
    ProfessorRepository pr;
    CursoRepository c;

    @GetMapping(value = "")
    @ResponseBody
    public ModelAndView professorInicio() 
        ModelAndView form = new ModelAndView("/form");
        form.addObject("professor", new Professor());
        List<Curso> curso = c.findAll();
        curso.get(0).getId();
        form.addObject("curso", curso);
        return form;
    

    @PostMapping(value = "")
    @ResponseBody
    public ModelAndView cadastraProfessor(@ModelAttribute ("professor") Professor professor)
        //Professor prof = new Professor();
        ModelAndView index = new ModelAndView("/index");
        professor.getUsername();
        professor.getEmail();
        professor.getNome();
        professor.getCursoCoord();
        pr.save(professor);

        return index;
    

 ....


<form th:action="@/professor" th:object = "$professor" method="POST">

            <div class = "form-group">
                <label for = "username">Username</label>
                <input type = "text" th:field = "*username" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                    <label for = "nome">Nome</label>
                    <input type = "text" th:field = "*nome" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                    <label for = "email">Email</label>
                    <input type = "hidden" name="email" value="">
                    <input type = "text" th:field = "*email" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                <select th:field = "*curso_coord">
                    <option 
                    th:each = "c: $cursos"
                    th:value = "$c.id">Cursos
                    </option>
                    <option value = -1> Não Coordenador
                    </option>
                </select>"
            </div>
            <button type = "submit" class = "btn btn-success ">Salvar</button>
        </form>

2019-10-04 15:37:00.700 错误 17580 --- [nio-8081-exec-1] c.p.p.controller.ErrorController : 算法错误！

java.lang.NullPointerException: null 在 com.planoensino.planoensino.controller.ProfessorController.professorInicio（ProfessorController.java:35） 〜[主要/：na] 在 sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181] 在 sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_181] 在 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_181] 在 java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_181] 在 org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:877) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:783) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) [spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:866) [spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:687) [javax.servlet-api-3.1.0.jar:3.1.0] 在 org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) [spring-webmvc-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [javax.servlet-api-3.1.0.jar:3.1.0] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:119) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) [spring-security-web-5.0.7.RELEASE.jar:5.0.7.RELEASE] 在 org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.session.web.http.SessionRepositoryFilter.doFilterInternal(SessionRepositoryFilter.java:147) [spring-session-core-2.0.5.RELEASE.jar:2.0.5.RELEASE] 在 org.springframework.session.web.http.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:81) [spring-session-core-2.0.5.RELEASE.jar:2.0.5.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.8.RELEASE.jar:5.0.8.RELEASE] 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.StandardWrapperValve.invoke（StandardWrapperValve.java:198） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:96） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.authenticator.AuthenticatorBase.invoke（AuthenticatorBase.java:493） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:140） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:81） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:87） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:342） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.coyote.AbstractProcessorLight.process（AbstractProcessorLight.java:66） [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:800) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1471) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_181] 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_181] 在 org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.32.jar:8.5.32] 在 java.lang.Thread.run(Thread.java:748) [na:1.8.0_181]

2019-10-04 15:37:00.702 警告 17580 --- [nio-8081-exec-1] .m.m.a.ExceptionHandlerExceptionResolver : 已解决的异常导致 通过Handler执行：java.lang.NullPointerException

【参考方案1】：

你忘了把@Autowired放在CursoRepository c上

只需通过替换现有的代码来修改代码：

@Autowired
CursoRepository c;

【参考方案2】：

CursoRepository c;

不是Spring托管的bean，试试

@Autowired
ProfessorRepository pr;

@Autowired
CursoRepository c;

【参考方案3】：

缺少为CursoRepository添加@Autowired annotation，这就是空指针异常的原因。

@Autowired
CursoRepository c;