在基于 Spring MVC 的项目上工作时，我在尝试保存评论(Bean)时收到以下代码。我能够成功地将数据输入 Controller ，但由于某种原因在保存时出现 NULL 指针异常。
这是代码
-- JSP--
<div class="col-md-12">
<div class="p-b">
<cf:form action="${pageContext.request.contextPath}/reviews/add" id="reviewAction" modelAttribute="review" method="post" accept-charset="utf-8">
<div style="display:none">
<cf:input path="tutorId" type="hidden" name="tutorId" id="tutorId" value="" />
<cf:input path="studentId" type="hidden" name="studentId" id="studentId" value="${sessionScope.user.userId}" />
</div>
<label>Your Comment / Review</label>
<cf:textarea path="reviewMessage" name="reviewMessage" required="required"/>
<p class="text-right"><input type="submit" class="btn btn-default btn-sm" name="submit" value="Post"> </p>
</cf:form>
</div>
</div>
<cf:hidden path="userId" id="userId"/>
<script type="text/javascript">
$(document).ready(function () {
console.log("Calling getTutorId()");
getTutorId();
});
function getTutorId()
{
$('#tutorId').attr('value',$('#userId').val());
}
</script>
-- Controller --
@RequestMapping (value = "/add" , method = RequestMethod.POST)
public String addReview(@Valid @ModelAttribute Review review , BindingResult bindingResult, Model model) {
try {
if (bindingResult.hasErrors()) {
System.out.println(bindingResult.getAllErrors().iterator().next().toString());
return "FindTutor";
}
DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
Date date = new Date();
String newDate = dateFormat.format(date); //06/08/2016 15:59:48
review.setDate(newDate);
review.setReviewStatus("Disapproved");
//Just for testing purposes
System.out.println(review.getStudentId());
System.out.println(review.getTutorId());
System.out.println(review.getDate());
System.out.println(review.getReviewMessage());
System.out.println(review.getReviewStatus());
//Just for testing purposes
reviewBL.saveReview(review);
List<Subject> subjectList = subjectBL.getAllSubjects();
List<User> userList = manageUserBL.getAllUsers();
model.addAttribute("subjectList", subjectList);
model.addAttribute("userList", userList);
} catch (Exception e) {
e.printStackTrace();
}
return "FindTutor";
}
-- 业务逻辑类 --
@Service
public class ReviewBL {
private ReviewsMongoRepository reviewsMongoRepository;
public void saveReview(Review review)
{
if (StringUtils.isEmpty(review.getId())) {
review.setId(null);
}
reviewsMongoRepository.save(review);
}
}
-- Bean 类 --
@Document (collection = "reviews")
public class Review {
@Id
private String Id;
private String tutorId;
private String studentId;
private String date;
private String reviewMessage;
private String reviewStatus;
// plus constructors also all of the getters and setters
}
我收到以下错误消息，正如您所看到的数据(模型属性已在 Controller 中成功捕获，但由于 NULL 指针异常错误而未保存在数据库中，我似乎无法找出原因
2016-05-28 13:16:59 [http-bio-8080-exec-6] INFO e.b.fyp.stp.web.filter.SessionFilter - Filtering: /reviews/add
java.lang.NullPointerException
at edu.bnu.fyp.stp.bl.ReviewBL.saveReview(ReviewBL.java:23)
at edu.bnu.fyp.stp.web.controller.student.ReviewController.addReview(ReviewControll er.java:66)
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:606)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:869)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at edu.bnu.fyp.stp.web.filter.SessionFilter.doFilter(SessionFilter.java:59)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:436)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
574939f19fcf9da523b63f8b // ID 1 (String)
57493a3e9fcf9da523b63f8c // ID 2 (String)
28/05/2016 13:16:59 //Date (String)
Great Tutor // Message (String)
Disapproved //Status (String)
2016-05-28 13:16:59 [http-bio-8080-exec-6] INFO e.b.fyp.stp.web.filter.SessionFilter - Filtering: /WEB-INF/jsp/FindTutor.jsp
最佳答案
我能够解决这个问题。这是因为我没有在reviewsMongoRepository上应用@Autowired，所以它没有与review bean链接。我纠正了这个问题，现在它可以工作了。谢谢您
关于java - 保存 ModelAttribute 时出现空指针异常 [Spring MVC]，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37503756/