Spring 表单验证错误：java.lang.IllegalArgumentException：'items' 不能为 null

Question

提问by Chandra Prakash

I am trying to Validate Springform which includes:

我正在尝试Validate Spring形成其中包括：

Normal input fields
Radio buttons whose options are set in controller (later may come from database)
Check box whose options are also set in controller
Select field which is also set in controller

普通输入字段
其选项在控制器中设置的单选按钮（稍后可能来自数据库）
其选项也在控制器中设置的复选框
选择也在控制器中设置的字段

Method 1 approach is followed.

遵循方法1方法。

Model:

模型：

public class Student {
    private Long id;

    @NotEmpty
    private String name;

    @NotEmpty
    private String address;

    @NotEmpty
    private String contactNumber;

    @NotEmpty
    private String grade;

    @NotEmpty
    private String gender;

    @NotEmpty
    @Email
    private String email;

    @NotEmpty
    private List<String> extraSubjects = new ArrayList<String>();

    /****  Corresponding getter setters ****/

}

Controller:-

控制器：-

@Controller
@RequestMapping("/student")
public class StudentController {
    private Logger logger = Logger.getLogger(StudentController.class);

    @RequestMapping("/home")
    public String getHomePage() {
        return "home";
    }

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String addStudentForm(Model model) {
        Student student = new Student();
        model.addAttribute("studentForm", student);

        LinkedHashMap<Integer, String> gradeList = new LinkedHashMap<Integer, String>();
        gradeList.put(1, "Class 1");
        gradeList.put(2, "Class 2");
        gradeList.put(3, "Class 3");
        gradeList.put(4, "Class 4");
        gradeList.put(5, "Class 5");
        model.addAttribute("gradeList", gradeList);

        List<String> genderList = new ArrayList<String>();
        genderList.add("Male");
        genderList.add("Female");
        model.addAttribute("genderList", genderList);
        student.setGender("Male");

        List<String> extraSubjects = new ArrayList<String>();
        extraSubjects.add("Math II");
        extraSubjects.add("Population");

        List<String> extraSubjectsStd = new ArrayList<String>();
        extraSubjectsStd.add("Math II");
        extraSubjectsStd.add("Population");
        student.setExtraSubjects(extraSubjectsStd);

        extraSubjects.add("Computer");
        model.addAttribute("extraSubjects", extraSubjects);
        return "addstudent";
    }

    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public String addStudent(
            @Valid @ModelAttribute("studentForm") Student student,
            BindingResult result) {

        if (result.hasErrors()) {
            logger.info("Returning add page with errors");
            return "addstudent";
        }
            //Stuffs to save in database 
        return "redirect:add";
    }
}

JSP Page:-

JSP页面：-

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://www.springframework.org/tags" prefix="spring"%>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Insert title here</title>
<style>
.error {
    color: #ff0000;
}

.errorblock {
    color: #000;
    background-color: #ffEEEE;
    border: 3px solid #ff0000;
    padding: 8px;
    margin: 16px;
}
</style>
</head>
<body>
    <form:form action="add" method="post" commandName="studentForm">
        <form:errors path="*" cssClass="errorblock" element="div" />
        <table border="0">
            <tr>
                <td colspan="3" align="center"><h3>Add Student</h3></td>
            </tr>
            <tr>
                <td><form:label path="name">
                        <spring:message code="label.studentname" />
                    </form:label></td>
                <td><form:input path="name" /></td>
                <td><form:errors path="name" cssClass="error" /></td>
            </tr>
            <tr>
                <td><form:label path="address">
                        <spring:message code="label.address" />
                    </form:label></td>
                <td><form:input path="address" /></td>
                <td><form:errors path="address" cssClass="error" />
            </tr>
            <tr>
                <td>Contact Number:</td>
                <td><form:input path="contactNumber" /></td>
                <td><form:errors path="contactNumber" cssClass="error" />
            </tr>
            <tr>
                <td><form:label path="grade">
                        <spring:message code="label.grade" />
                    </form:label></td>
                <td><form:select path="grade">
                        <form:option value="" label="--- Select ---" />
                        <form:options items="${gradeList}" />
                    </form:select></td>
                <td><form:errors path="grade" cssClass="error" />
            </tr>
            <tr>
                <td>Gender:</td>
                <td><form:radiobuttons path="gender" items="${genderList}" />
                </td>
                <td><form:errors path="gender" cssClass="error" />
            </tr>
            <tr>
                <td>Extra Subjects:</td>
                <td><form:checkboxes items="${extraSubjects}"
                        path="extraSubjects" /></td>
                <td><form:errors path="extraSubjects" cssClass="error" />
            </tr>
            <tr>
                <td>Email Address:</td>
                <td><form:input items="${email}" path="email" /></td>
                <td><form:errors path="email" cssClass="error" />
            </tr>
            <tr>
                <td></td>
                <td align="center"><input type="submit" value="Save" /></td>
                <td></td>
            </tr>
        </table>
    </form:form>
</body>
</html>

Now, When I run my application, the forms get loaded while I perform get operation. The value in the radio buttons, select fields, and checkboxes are loadedand selected as well. If I submit my form with no validation errors it works finebut when I send my form with validation errors, I get following errors:

现在，当我运行我的应用程序时，表单会在我perform get operation. radio buttons, select fields, and checkboxes are loaded和 selected 中的值也是如此。如果我submit my form with no validation errors it works fine但是当我发送表单时with validation errors，我会收到以下错误：

StackTrace:-

堆栈跟踪：-

Jun 26, 2014 4:32:00 PM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.IllegalArgumentException: 'items' must not be null
    at org.springframework.util.Assert.notNull(Assert.java:112)
    at org.springframework.web.servlet.tags.form.AbstractMultiCheckedElementTag.setItems(AbstractMultiCheckedElementTag.java:85)
    at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspx_meth_form_005fradiobuttons_005f0(addstudent_jsp.java:810)
    at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspService(addstudent_jsp.java:360)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:266)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1225)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1012)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:931)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:833)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    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:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

DEBUG org.springframework.web.servlet.DispatcherServlet- Error rendering view [org.springframework.web.servlet.view.JstlView: name 'addstudent'; URL [/WEB-INF/pages/addstudent.jsp]] in DispatcherServlet with name 'mvc-dispatcher'
org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/pages/addstudent.jsp at line 62

59:             </tr>
60:             <tr>
61:                 <td>Gender:</td>
62:                 <td><form:radiobuttons path="gender" items="${genderList}" />
63:                 </td>
64:                 <td><form:errors path="gender" cssClass="error" />
65:             </tr>    

Stacktrace:
        at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
        at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
        at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
        at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
        at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
        at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:266)
        at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1225)
        at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1012)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:931)
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:833)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        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:501)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
    Caused by: java.lang.IllegalArgumentException: 'items' must not be null
        at org.springframework.util.Assert.notNull(Assert.java:112)
        at org.springframework.web.servlet.tags.form.AbstractMultiCheckedElementTag.setItems(AbstractMultiCheckedElementTag.java:85)
        at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspx_meth_form_005fradiobuttons_005f0(addstudent_jsp.java:810)
        at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspService(addstudent_jsp.java:360)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
        ... 42 more
    Jun 26, 2014 4:32:00 PM org.apache.catalina.core.StandardWrapperValve invoke
    SEVERE: Servlet.service() for servlet [mvc-dispatcher] in context with path [/sms] threw exception [An exception occurred processing JSP page /WEB-INF/pages/addstudent.jsp at line 62

    59:             </tr>
    60:             <tr>
    61:                 <td>Gender:</td>
    62:                 <td><form:radiobuttons path="gender" items="${genderList}" />
    63:                 </td>
    64:                 <td><form:errors path="gender" cssClass="error" />
    65:             </tr>


    Stacktrace:] with root cause
    java.lang.IllegalArgumentException: 'items' must not be null
        at org.springframework.util.Assert.notNull(Assert.java:112)
        at org.springframework.web.servlet.tags.form.AbstractMultiCheckedElementTag.setItems(AbstractMultiCheckedElementTag.java:85)
        at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspx_meth_form_005fradiobuttons_005f0(addstudent_jsp.java:810)
        at org.apache.jsp.WEB_002dINF.pages.addstudent_jsp._jspService(addstudent_jsp.java:360)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
        at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
        at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
        at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
        at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:209)
        at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:266)
        at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1225)
        at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1012)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:931)
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:833)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        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:501)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

I am able to figure out that the Listthat I have used for specifying genders, gradeList, extraSubjectsare appear to be NULL after post request.

我能够弄清楚List我使用过specifying genders, gradeList, extraSubjects的似乎是NULL after post request.

How can I render those values again in form after post if validation fails?
Should I have to set the value in lists on POST method too as in GET method?

如果验证失败，如何在发布后再次在表单中呈现这些值？
我是否也必须像在 GET 方法中一样在 POST 方法的列表中设置值？

Answer 1

采纳答案by Serge Ballesta

In you get part, you populate you model, not only with studentFormbut also with genderList, gradeListand extraSubjects. And you use all in your jsp.

在你得到部分，你填充你的模型，不仅用studentForm而且用genderList,gradeList和extraSubjects。你在你的jsp中使用all。

In the post part, you have a studentForminitialized by the parameters in the request. But your never initialize the lists. So in the JSP, ${gradeList}, ${genderList}and ${extraSubjects}and all null, so the error.

在 post 部分，您已经studentForm通过请求中的参数进行了初始化。但是您从不初始化列表。所以在 JSP 中，${gradeList},${genderList}和${extraSubjects}都为空，所以报错。

You have to initialize the three lists in addStudentbefore forwarding to the view if validation fails. You can do that either as proposed by Neil McGuigan, ie by having spring to automatically populate the model, or by populating it yourself. For example, you could have :

addStudent如果验证失败，您必须在转发到视图之前初始化三个列表。您可以按照 Neil McGuigan 的建议执行此操作，即让 spring 自动填充模型，或者自己填充模型。例如，你可以有：

void initLists(Model model) {
    LinkedHashMap<Integer, String> gradeList = new LinkedHashMap<Integer, String>();
    gradeList.put(1, "Class 1");
    gradeList.put(2, "Class 2");
    gradeList.put(3, "Class 3");
    gradeList.put(4, "Class 4");
    gradeList.put(5, "Class 5");
    model.addAttribute("gradeList", gradeList);

    List<String> genderList = new ArrayList<String>();
    genderList.add("Male");
    genderList.add("Female");
    model.addAttribute("genderList", genderList);

    List<String> extraSubjects = new ArrayList<String>();
    extraSubjects.add("Math II");
    extraSubjects.add("Population");
    extraSubjects.add("Computer");
    model.addAttribute("extraSubjects", extraSubjects);
}

and call initListsboth in addStudentFormand in addStudent. Example code for last :

并调用initListsinaddStudentForm和 in addStudent。last 的示例代码：

@RequestMapping(value = "/add", method = RequestMethod.POST)
public String addStudent(
        @Valid @ModelAttribute("studentForm") Student student,
        BindingResult result, Model model) {

    if (result.hasErrors()) {
        logger.info("Returning add page with errors");
        initLists(model);
        return "addstudent";
    }
        //Stuffs to save in database 
    return "redirect:add";
}

Of course, all list initialization should be removed from addStudentFormonce you call initListsfrom there ...

当然，addStudentForm一旦你initLists从那里打电话，所有的列表初始化都应该被删除......

Answer 2

回答by Neil McGuigan

Change your controller to be like this:

将您的控制器更改为如下所示：

@Controller
@RequestMapping("/student")
@SessionAttributes({"studentForm", "gradeList", "genderList", "extraSubjects"})
public class StudentController {
    private Logger logger = Logger.getLogger(StudentController.class);

    @ModelAttribute("studentForm")
    Student getStudent() {
      Student student = new Student();
      student.setGender("Male");

      List<String> extraSubjectsStd = new ArrayList<String>();
      extraSubjectsStd.add("Math II");
      extraSubjectsStd.add("Population");
      student.setExtraSubjects(extraSubjectsStd);

      return student;
    }

    @ModelAttribute("gradeList")
    GradeList getGradeList() {
        LinkedHashMap<Integer, String> gradeList = new LinkedHashMap<Integer, String>();
        gradeList.put(1, "Class 1");
        gradeList.put(2, "Class 2");
        gradeList.put(3, "Class 3");
        gradeList.put(4, "Class 4");
        gradeList.put(5, "Class 5");
        return gradeList;
    }

    @ModelAttribute("genderList")
    List<String> getGenderList() {
        List<String> genderList = new ArrayList<String>();
        genderList.add("Male");
        genderList.add("Female");
        return genderList;
    }

    @ModelAttribute("extraSubjects")
    List<String> getExtraSubjects() {
        List<String> extraSubjects = new ArrayList<String>();
        extraSubjects.add("Math II");
        extraSubjects.add("Population");
        extraSubjects.add("Computer");
        return extraSubjects;
    }

    @RequestMapping("/home")
    public String getHomePage() {
        return "home";
    }

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String addStudentForm() {

        return "addstudent";
    }

    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public String addStudent(
            @Valid @ModelAttribute("studentForm") Student student,
            BindingResult result,
            SessionStatus sessionStatus) {

        if (result.hasErrors()) {
            logger.info("Returning add page with errors");
            return "addstudent";
        }
        sessionStatus.setComplete();

            //Stuffs to save in database 
        return "redirect:add";
    }
}

While we're at it:

当我们在做的时候：

Your data like gradeList should probably be in a database.
/student URL should be /students
Home page should be in its own controller

您的数据如 gradeList 可能应该在数据库中。
/student URL 应该是 /students
主页应该在它自己的控制器中

Spring 表单验证错误：java.lang.IllegalArgumentException：'items' 不能为 null

提问by Chandra Prakash

采纳答案by Serge Ballesta

回答by Neil McGuigan

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Spring 表单验证错误：java.lang.IllegalArgumentException：'items' 不能为 null

提问by Chandra Prakash

采纳答案by Serge Ballesta

回答by Neil McGuigan

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