java - JSP下拉不提交对象

Question

我有一个表单，其中填充了来自数据库的数据。 在开始描述我的问题之前，先看一些片段:

一类:

// @Entity for areas
public class Area {
@Id
@Column(name = "area")
private String area;

@Column(name = "deleted")
private boolean deleted;

getter/setter
}

二等舱

// @Entity for employees
public class Employee {
@Id
@GeneratedValue
@Column(name = "ID")
private long id;

@ManyToOne
@JoinColumn(name = "area")
private Area area;

@Column(name = "name")
private String name;

getter/setter

调用EmployeeController中的方法返回数据给jsp

protected String createDialog( @PathVariable("id") Long id, Model model ){
    Employee employee = id == 0 ? new Employee() : employeeService.findById(id);
    //return employee
    model.addAttribute("employeeModel", employee );
 //add data needed to create dropdown holding areas
    //areaService.findAll returns a List<Area>
    model.addAttribute("areas", areaService.findAll( 
                new Sort( 
                    Sort.Direction.ASC,
                    "area"
                    )
                ));
    return "employees/dialogUpdateEdit";
}

jsp，显示区域的下拉列表，如果没有返回新员工，则显示已知数据

<form:form action="employees/ajax" commandName="employeeModel" method="POST" id="createForm">
    <table class="fullWidth">
        <tr>
            <td>Area</td>
            <td>
                <form:select path="area" items="${areas}" class="fullWidth">
                </form:select>
            </td>
        </tr>
        <tr>
            <td>Employee Name</td>
            <td><form:input path="name" class="fullWidth"/></td>
        </tr>
        <tr>
            <td colspan="2">
                <input type="submit" value="Save Changes" id="btnSaveEmployee" class="fullWidth" />
            </td>
        </tr>
    </table>

    <!-- adding hidden field to hold id on update -->
<form:hidden path="id" />   

</form:form>

Controller 方法进行验证并返回或不返回一些错误

@RequestMapping(value = "/ajax", method = RequestMethod.POST)
protected @ResponseBody ValidationResponse createOrUpdate(
        @Validated @ModelAttribute("employeeModel") Employee employee,
        BindingResult bindingResult) {

    if (!bindingResult.hasErrors()) {
        employeeService.createOrUpdate(employee);
    }

    return validate(employee, null, bindingResult);
}

对于问题: 这一切都很好，下拉列表被填充，数据被填充到输入中。 但是当我点击提交时，出现以下错误:

java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.whatever.Area] for property 'area': no matching editors or conversion strategy found

据我所知，表单只是提交“区域”的纯字符串，而不是绑定(bind)列表中的对象。

如何让表单提交对象而不是字符串？我的绑定(bind)有问题吗？

感谢您的帮助!

Answer 1

回答我自己的问题，并希望那个在不知情的情况下帮助我的人得到很多学分；)

我不得不添加一个自定义 Binder ...以前从未听说过，所以我先问了很长的路要走。

自从我知道自己在寻找什么以来，此链接包含关于该主题的最好和最短的教程: http://empire5.com/development/binding-a-custom-object-in-spring-3/