How to populate dropdown box in Spring MVC
drop-down-menu, java, jsp, spring, spring-mvc
Solution
Not sure what Controller method is called to show your view with `documentNumberList`, but you need to add that collection to the model passed to this view:
model.addAttribute("documentNumberList", documentService.retrieveAllDocumentNumbers());
Though from your exception stack trace you also missed an @Autowired on `documentService` field.
Problem
I have been trying to find out how to populate a dropdown box in Spring MVC. There are a few threads out there on this subject but none of them that I have found have helped me so I'm hoping someone here can help me out. Here is my controller: ``` @Controller @RequestMapping("/document-revision") public class DocumentRevisionController { @Autowired private DocumentRevisionService documentRevisionService; private DocumentService documentService; @RequestMapping(value="/list", method=RequestMethod.GET) public String getDocumentRevisionList(Model model) { List<DocumentRevision> documentRevisions = documentRevisionService.retrieveAllDocumentRevisions(); model.addAttribute("documentRevisions", documentRevisions); return "document-revision"; } @RequestMapping(value="/add", method=RequestMethod.GET) public String getDocumentRevision(Model model) { DocumentRevision documentRevision = new DocumentRevision(); model.addAttribute("documentRevisionAttribute", documentRevision); return "new-documnent-revision"; } @RequestMapping(value="/add", method=RequestMethod.POST) public String postDocumentRevision(@ModelAttribute("documentRevisionAttribute") @Valid DocumentRevision documentRevision, BindingResult result) { if(result.hasErrors()){ return "new-document-revision"; } documentRevisionService.createDocumentRevision(documentRevision); return "redirect:/testapp/document-revision/list"; } } ``` and here is the jsp page: ``` <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Insert title here</title> <style> .error { color: red; } </style> </head> <body> <h1>Create New Document Revision</h1> <c:url var="saveUrl" value="/testapp/document-revision/add" /> <form:form modelAttribute="documentRevisionAttribute" method="POST" action="${saveUrl}"> <table> <tr> <td>DocumentNumber</td> <td><form:select path="document_number"> <form:option value="NONE" label="--- Select ---" /> <form:options items="${documentNumberList}" /> </form:select> </td> <td><form:errors path="document_number" cssClass="error" /></td> </tr> <tr> <td><form:label path="documentRState">Document R-State</form:label></td> <td><form:input path="documentRState"/></td> <td><form:errors path="documentRState" cssClass="error"/></td> </tr> </table> <input type="submit" value="Save" /> </form:form> </body> </html> ``` I have tried adding a @ModelAttribute method which retrieves the document numbers, ``` @ModelAttribute public List<Document> documentNumberList(){ return documentService.retrieveAllDocumentNumbers(); } ``` but it gave me errors. Is there anyone who knows how it should be done? Thank you for your time /D Edit I thought I'd clarify that my wish is to have a dropdown box for the document numbers which are retrieved by the documentService. Edit 2 Here is the error log as requested: ``` java.lang.NullPointerException testapp.controller.DocumentRevisionController.documentNumberList(DocumentRevisionController.java:33) sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) java.lang.reflect.Method.invoke(Method.java:601) org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:212) org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126) org.springframework.web.method.annotation.ModelFactory.invokeModelAttributeMethods(ModelFactory.java:123) org.springframework.web.method.annotation.ModelFactory.initModel(ModelFactory.java:97) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:614) org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578) org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:900) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:827) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778) javax.servlet.http.HttpServlet.service(HttpServlet.java:621) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) ``` Solution I thought I would add the complete controller code that works in case there are others who could benefit from it: ``` @Controller @RequestMapping("/document-revision") public class DocumentRevisionController { @Autowired private DocumentRevisionService documentRevisionService; @Autowired private DocumentService documentService; @RequestMapping(value="/list", method=RequestMethod.GET) public String getDocumentRevisionList(Model model) { List<DocumentRevision> documentRevisions = documentRevisionService.retrieveAllDocumentRevisions(); model.addAttribute("documentRevisions", documentRevisions); return "document-revision"; } @RequestMapping(value="/add", method=RequestMethod.GET) public String getDocumentRevision(Model model) { DocumentRevision documentRevision = new DocumentRevision(); model.addAttribute("documentRevisionAttribute", documentRevision); model.addAttribute("documentNumberList", documentService.retrieveAllDocumentNumbers()); return "new-documnent-revision"; } @RequestMapping(value="/add", method=RequestMethod.POST) public String postDocumentRevision(@ModelAttribute("documentRevisionAttribute") @Valid DocumentRevision documentRevision, BindingResult result) { if(result.hasErrors()){ return "new-document-revision"; } documentRevisionService.createDocumentRevision(documentRevision); return "redirect:/testapp/document-revision/list"; } } ```