Reputation: 3274
I want to save a Student record with say following form
<form:form commandName="std" method="POST" >
<form:input type="text" path="name"/>
<label>Subjects</label>
<form:select path="subjects" multiple="multiple">
<form:option value="English">English</form:option>
<form:option value="Maths">Maths</form:option>
</form:select>
<input type="submit" value="Save">
</form:form>
In controller I have a binder as
@InitBinder
public void initSubjectBinder(WebDataBinder binder) {
binder.registerCustomEditor(Subject.class,
new PropertyEditorSupport() {
@Override
public void setAsText(String text) {
Subject subject = new Subject();
subject.setSubjectName(text);
System.out.println("Saving Subject Object...");
subjectService.save(subject);
}
});
}
the above initSubjectBinder()
saves Subject object, but subject is not assigned to Student. In POST
method I want to add Student to those selected subjects
@RequestMapping(value = "/save-std", method = RequestMethod.POST)
public String saveStd(@ModelAttribute("std") Student std) {
try {
System.out.println("List size is " + std.getSubjects().size()); // Here it says List Size is 4 (if four subjects are selected)
for (Subject subject : std.getSubjects()) {
subject.setStudent(std); // Here it gives NPE see stackTrace for more info
subjectService.update(subject);
}
} catch (Exception e) {
System.out.println("Error is " + e.getMessage());
}
return "home";
}
I get Hibernate results in console as
Saving Subject Object...
Hibernate:
insert
into
Subject
(studentId, subjectName)
values
(?, ?)
Saving Subject Object...
Hibernate:
insert
into
Subject
(studentId, subjectName)
values
(?, ?)
Saving Subject Object...
Hibernate:
insert
into
Subject
(studentId, subjectName)
values
(?, ?)
Saving Subject Object...
Hibernate:
insert
into
Subject
(studentId, subjectName)
values
(?, ?)
Hibernate:
insert
into
Student
(studentName)
values
(?)
List size is 4 (Result of System.out.println("List size is " + std.getSubjects().size()); )
Error is null (Result of System.out.println("Error is " + e.getMessage());)
and the stack-trace is
java.lang.NullPointerException at com.app.web.HomeController.saveStd(HomeController.java:76) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) 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:966) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868) at javax.servlet.http.HttpServlet.service(HttpServlet.java:650) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842) 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 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.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)
Now that is hard to understand where and why NPE occurs and how should I assign subjects to Student?
Upvotes: 0
Views: 62
Reputation: 3274
Thanks to @PavelHoral, He pointed out my mistake after making some changes I came up with
@InitBinder
public void initSubjectBinder(WebDataBinder binder) {
binder.registerCustomEditor(Subject.class,
new PropertyEditorSupport() {
@Override
public void setAsText(String text) {
Subject subject = new Subject();
subject.setSubjectName(text);
setValue(subject); // This is the turning point for me
}
});
}
and in controller method
@RequestMapping(value = "/save-std", method = RequestMethod.POST)
public String saveStd(@ModelAttribute("std") Student std) {
try {
System.out.println("List size is " + std.getSubjects().size());
for (Subject subject : std.getSubjects()) {
subject.setStudent(std);
subjectService.save(subject);
}
} catch (Exception e) {
System.out.println("Error is " + e.getMessage());
}
return "home";
}
and it worked and my issue was resolved.
Upvotes: 0