如何在Spring MVC中填充下拉框

问题内容：

我一直试图找出如何在Spring MVC中填充一个下拉框。关于这个主题有一些线索，但是我发现没有一个线索对我有帮助，所以我希望这里的人可以帮助我。

这是我的控制器：

@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";  
}

}

这是jsp页面：

<%@ 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>

我尝试添加一个@ModelAttribute方法来检索文档编号，

        @ModelAttribute
    public List<Document> documentNumberList(){
        return documentService.retrieveAllDocumentNumbers();
    }

但这给了我错误。有谁知道应该怎么做？

感谢您的时间

/ D

编辑我想澄清一下，我希望有一个下拉框，用于显示由documentService检索的文档编号。

编辑2 这是请求的错误日志：

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)

解决方案 我想我会添加完整的控制器代码，以防万一其他人可以从中受益：

@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";  
}

}

问题答案：

不确定调用哪个Controller方法来显示带有的视图documentNumberList，但是您需要将该集合添加到传递给该视图的模型中：

model.addAttribute("documentNumberList", documentService.retrieveAllDocumentNumbers());

尽管从异常堆栈跟踪中您也错过了@Autowired on documentService字段。

如何在Spring MVC中填充下拉框

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