如何正确使用Spring MVC <form:select> tag以将特定对象字段的值显示到集合中？

Question

I am pretty new in Spring MVC and I have some difficulties to understand how exactly works the 我是Spring MVC的新手，我很难理解究竟是如何工作的 tag. 标签。

So I have the following situation. 所以我有以下情况。

Into a controller I have this method: 进入控制器我有这个方法：

@RequestMapping(value = "/consultazioneMinisteriale", method = RequestMethod.GET)
public String consultazione(Locale locale, Model model) {

    List<Twb1012Regione> listaRegioni = geograficaService.getListaRegioni();

    System.out.println("Numero regioni: " + listaRegioni.size());

    model.addAttribute("listaRegioni", listaRegioni);

    return "utenteMinisteriale/consultazione";
}

As you can see this method retrieve a List of Twb1012Regione object and put it into the model object so it will be available into the consultazione.jsp page. 正如您所看到的，此方法检索Twb1012Regione对象的List并将其放入模型对象中，以便可以在consultazione.jsp页面中使用。

So the Twb1012Regione class is a model object like this: 所以Twb1012Regione类是这样的模型对象：

@Entity
@Table(name="anagrafiche.TWB1012_REGIONE")
@NamedQuery(name="Twb1012Regione.findAll", query="SELECT t FROM Twb1012Regione t")
public class Twb1012Regione implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name="COD_REG")
    private String codReg;

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

    .....................................
    .....................................
    OTHER FIELDS
    .....................................
    .....................................
}

Where the codReg field univocally identify the object and the desReg contain the value that I want to show as value into the codReg字段唯一地标识对象， desReg包含我想要显示为值的值 tag. 标签。

Finnaly this is the code of my consultazione.jsp view: Finnaly这是我的consultazione.jsp视图的代码：

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
<%@ page session="false"%>
<%@  taglib prefix="security" uri="http://www.springframework.org/security/tags" %>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>

<!DOCTYPE html>
<html>
    <head>
        <title>Home</title>
    </head>

    <body class="azure">
        <h1>Hello World</h1>

        <!--  <div> ${listaRegioni} </div> -->


        <div>
            <label>Regioni:</label>
            <form:select path="listaRegioni" items="${listaRegioni}"/>
        </div>

    </body>
</html>

The problem is that doing in this way I obtain the select dropdown but it show the reference of all my Twb1012Regione objects and not the name of the desReg field. 问题是，这样做我获得了选择下拉列表，但它显示了我所有Twb1012Regione对象的引用，而不是desReg字段的名称。

This is the HTML rendered output: 这是HTML呈现的输出：

<select>
    <option value="it.myCompany.myProject.anagrafiche.Twb1012Regione@5a259924">it.myCompany.myProject.anagrafiche.Twb1012Regione@5a259924</option>
    <option value="it.myCompany.myProject.anagrafiche.Twb1012Regione@4a87c8d3">it.myCompany.myProject.anagrafiche.Twb1012Regione@4a87c8d3</option>
    <option value="it.myCompany.myProject.anagrafiche.Twb1012Regione@815b53a">it.myCompany.myProject.anagrafiche.Twb1012Regione@815b53a</option>
    .................................................
    .................................................
    .................................................
</select>

Why? 为什么？ What am I missing? 我错过了什么？ How can I shoe the value of the desReg field of each Twb1012Regione instead the reference of the objects? 我怎样才能将每个Twb1012Regione的desReg字段的值换成对象的引用？

EDIT-1: 编辑-1：

I tryied to change into: 我试着换成：

<form:select path="regioni">
   <form:options items="${listaRegioni}" itemLabel="desReg" itemValue="codReg" />
</form:select>

But now when the page is rendered I obtain this error message into my stacktrace: 但是现在当页面呈现时，我将此错误消息发送到我的堆栈跟踪中：

12:44:52,112 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/WIFIPNSD].[jsp]] (http-localhost/127.0.0.1:8080-4) JBWEB000236: Servlet.service() for servlet jsp threw exception: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'regioni' available as request attribute

Why? 为什么？ What is wrong? 怎么了？ How can I solve it? 我该如何解决？

Answer 1

In <form:select> tag you must put in the path the name of the bean attribute will keep the id of the selected item . 在<form:select>标记中，您必须在path放置bean属性的名称将保留所选项的ID 。
In <form:options> : 在<form:options> ：
- items : the bean attribute containing the list of selectable items items ：包含可选项列表的bean属性
- itemLabel : the description to be shown in the dropbox itemLabel ：要在dropbox中显示的说明
- itemValue : the field to be saved (usually id) in the path of the <form:select> itemValue ：要在<form:select>的路径中保存的字段（通常为id）

<form:select path="regioni">
    <form:options items="${listaRegioni}" itemLabel="desReg" itemValue="codReg" />
</form:select>

Will show you a dropbox with all descriptions ( desReg ) of the regions, and will keep the the codReg of the selected item in the bean attribute regioni 会告诉你所有的描述（Dropbox的desReg的地区），并且将保持在codReg所选项目的在bean属性regioni

Answer 2

In your controller, add this line of code. 在您的控制器中，添加以下代码行。 Let me know : 让我知道：

model.addAttribute("regioni",new Twb1012Regione());

If it does not work, let me know. 如果它不起作用，请告诉我。

如何正确使用Spring MVC <form:select> tag以将特定对象字段的值显示到集合中？

问题描述

2 个解决方案

解决方案1
7 已采纳 2015-09-16 10:36:30

解决方案2
1 2015-09-16 11:14:56

如何正确使用Spring MVC <form:select> tag以将特定对象字段的值显示到集合中？

问题描述

2 个解决方案

解决方案1 7 已采纳 2015-09-16 10:36:30

解决方案2 1 2015-09-16 11:14:56

解决方案1
7 已采纳 2015-09-16 10:36:30

解决方案2
1 2015-09-16 11:14:56