我想在 Spring MVC 中填充一个下拉框我试图这样做但我得到空指针异常
这是我的控制器:
public class CatalogueController {
private CatalogueService catalogueService;
private PublisherService publisherService;
private SubjectService subjectService;
// some code and i generated setter and getter methods
............
@RequestMapping(value="/catalogue/new.action", method=RequestMethod.GET)
public ModelAndView newMember() throws Exception {
ModelAndView mvc= null;
mvc = new ModelAndView("catalogue/catalogueForm", "catalogueForm", new CatalogueBase());
mvc.addObject("copyDetailForm", new CatalogueCopyDetails());
List<Publisher> publist = publisherService.getPublisherList();
mvc.addObject("publist", publist);
List<Subject> subjectlist = subjectService.getSubjectList();
mvc.addObject("subjectlist", subjectlist);
return mvc;
}
这是我的服务方法:
@Override
public List<Publisher> getPublisherList() {
List<Publisher> list = publisherDAO.getPublisher();
return list;
}
@Override
public List<Subject> getSubjectList() {
List<Subject> list = subjectDAO.getSubjects();
return list;
}
这是我的 DAO 方法:
@SuppressWarnings("unchecked")
public List<Publisher> getPublisher() {
Query qry = getSession().createQuery("from Publisher");
return qry.list();
}
@SuppressWarnings("unchecked")
public List<Subject> getSubjects() {
Query qry = getSession().createQuery("from Subject");
return qry.list();
}
最后这是我的 JSP 页面:
<form:form commandname="catalogueForm" action="${pageContext.request.contextPath}/catalogue/create.action" method="post" modelAttribute="catalogueForm">
<form:select path="publisher.id" id="publisher.id">
<form:options items="${publist}" itemValue="id" itemLabel="name" />
</form:select>
<form:select path="subject.id" id="subject.id">
<form:options items="${subjectlist}" itemValue="id" itemLabel="name" />
</form:select>
</form:form>
这是堆栈跟踪:
java.lang.NullPointerException at com.easylib.elibrary.webapp.controller.catalogue.CatalogueController.newMember(CatalogueController.java:80) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl .java:57) 在 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 在 java.lang.reflect.Method.invoke(Method.java:601) 在 org.springframework.web.method.support.InvocableHandlerMethod。在 org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132) 处调用(InvocableHandlerMethod.java:219) java:100) 在 org.springframework.web。servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:604) 在 org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:565) 在 org.springframework.web。 servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) 在 org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)80) 在 org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)80) 在 org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)