Spring MVC-表单（Form）标签-下拉框（Dropdown）示例（转载实践）

以下内容翻译自：https://www.tutorialspoint.com/springmvc/springmvc_dropdown.htm

说明：示例基于Spring MVC 4.1.6。

以下示例显示如何使用Spring Web MVC框架在表单中使用Dropdown。首先，让我们使用Eclipse IDE，并按照以下步骤使用Spring Web Framework开发基于动态窗体的Web应用程序：

步骤	描述
1	创建一个名为HelloWeb的项目，在一个包com.tutorialspoint下，如Spring MVC - Hello World Example章节所述。
2	在com.tutorialspoint包下创建一个Java类User，UserController。
3	在jsp子文件夹下创建一个视图文件user.jsp，users.jsp。
4	最后一步是创建所有源和配置文件的内容并导出应用程序，如下所述。

User.java

package com.tutorialspoint;

public class User {

   private String username;
   private String password;
   private String address;
   private boolean receivePaper;
   private String [] favoriteFrameworks;
   private String gender;
   private String favoriteNumber;
   private String country;

   public String getUsername() {
      return username;
   }
   public void setUsername(String username) {
      this.username = username;
   }

   public String getPassword() {
      return password;
   }
   public void setPassword(String password) {
      this.password = password;
   }
   public String getAddress() {
      return address;
   }
   public void setAddress(String address) {
      this.address = address;
   }
   public boolean isReceivePaper() {
      return receivePaper;
   }
   public void setReceivePaper(boolean receivePaper) {
      this.receivePaper = receivePaper;
   }
   public String[] getFavoriteFrameworks() {
      return favoriteFrameworks;
   }
   public void setFavoriteFrameworks(String[] favoriteFrameworks) {
      this.favoriteFrameworks = favoriteFrameworks;
   }
   public String getGender() {
      return gender;
   }
   public void setGender(String gender) {
      this.gender = gender;
   }
   public String getFavoriteNumber() {
      return favoriteNumber;
   }
   public void setFavoriteNumber(String favoriteNumber) {
      this.favoriteNumber = favoriteNumber;
   }
   public String getCountry() {
      return country;
   }
   public void setCountry(String country) {
      this.country = country;
   }
}

UserController.java

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.ui.ModelMap;

@Controller
public class UserController {

   @RequestMapping(value = "/user", method = RequestMethod.GET)
   public ModelAndView user() {
      User user = new User();
      user.setFavoriteFrameworks((new String []{"Spring MVC","Struts 2"}));
      user.setGender("M");
      ModelAndView modelAndView = new ModelAndView("user", "command", user);
      return modelAndView;
   }

   @RequestMapping(value = "/addUser", method = RequestMethod.POST)
   public String addUser(@ModelAttribute("SpringWeb")User user,
      ModelMap model) {
      model.addAttribute("username", user.getUsername());
      model.addAttribute("password", user.getPassword());
      model.addAttribute("address", user.getAddress());
      model.addAttribute("receivePaper", user.isReceivePaper());
      model.addAttribute("favoriteFrameworks", user.getFavoriteFrameworks());
      model.addAttribute("gender", user.getGender());
      model.addAttribute("favoriteNumber", user.getFavoriteNumber());
      model.addAttribute("country", user.getCountry());
      return "users";
   }

   @ModelAttribute("webFrameworkList")
   public List<String> getWebFrameworkList()
   {
      List<String> webFrameworkList = new ArrayList<String>();
      webFrameworkList.add("Spring MVC");
      webFrameworkList.add("Struts 1");
      webFrameworkList.add("Struts 2");
      webFrameworkList.add("Apache Wicket");
      return webFrameworkList;
   }

   @ModelAttribute("numbersList")
   public List<String> getNumbersList()
   {
      List<String> numbersList = new ArrayList<String>();
      numbersList.add("1");
      numbersList.add("2");
      numbersList.add("3");
      numbersList.add("4");
      return numbersList;
   }

   @ModelAttribute("countryList")
   public Map<String, String> getCountryList()
   {
      Map<String, String> countryList = new HashMap<String, String>();
      countryList.put("US", "United States");
      countryList.put("CH", "China");
      countryList.put("SG", "Singapore");
      countryList.put("MY", "Malaysia");return countryList;
    }
}

这里第一个服务方法user()，我们已经通过名为“command”的ModelAndView对象中传递了一个空的User对象，因为如果您在JSP中使用<form:form>标签，Spring框架将期望一个名为“command”的对象文件。所以当user()方法被调用时，它返回user.jsp视图。

将在HelloWeb/addUser URL上针对POST方法调用第二个服务方法addUser()。您将根据提交的信息准备您的模型对象。最后，将从服务方法返回“user”视图，这将导致渲染users.jsp

user.jsp

<%@taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<html>
<head>
   <title>Spring MVC Form Handling</title>
</head>
<body>

<h2>User Information</h2>
<form:form method="POST" action="/HelloWeb/addUser">
   <table>
      <tr>
         <td><form:label path="username">User Name</form:label></td>
         <td><form:input path="username" /></td>
      </tr>
      <tr>
         <td><form:label path="password">Age</form:label></td>
         <td><form:password path="password" /></td>
      </tr>
      <tr>
         <td><form:label path="address">Address</form:label></td>
         <td><form:textarea path="address" rows="5" cols="30" /></td>
      </tr>
      <tr>
         <td><form:label path="receivePaper">Subscribe Newsletter</form:label></td>
         <td><form:checkbox path="receivePaper" /></td>
      </tr>
      <tr>
         <td><form:label path="favoriteFrameworks">Favorite Web Frameworks</form:label></td>
         <td><form:checkboxes items="${webFrameworkList}" path="favoriteFrameworks" /></td>
      </tr>
      <tr>
         <td><form:label path="gender">Gender</form:label></td>
         <td>
            <form:radiobutton path="gender" value="M" label="Male" />
            <form:radiobutton path="gender" value="F" label="Female" />
         </td>
      </tr>
      <tr>
         <td><form:label path="favoriteNumber">Favorite Number</form:label></td>
         <td>
            <form:radiobuttons path="favoriteNumber" items="${numbersList}" />
         </td>
      </tr>
      <tr>
         <td><form:label path="country">Country</form:label></td>
         <td>
            <form:select path="country">
               <form:option value="NONE" label="Select"/>
               <form:options items="${countryList}" />
            </form:select>
         </td>
      </tr>
      <tr>
         <td colspan="2">
            <input type="submit" value="Submit"/>
         </td>
      </tr>
   </table>
</form:form>
</body>
</html>

这里我们使用<form:select />，<form:option />和<form:options />标签来呈现HTML选择。例如

<form:select path="country">
   <form:option value="NONE" label="Select"/>
   <form:options items="${countryList}" />
</form:select>

它将呈现以下HTML内容。

<select id="country" name="country">
   <option value="NONE">Select</option>
   <option value="US">United States</option>
   <option value="CH">China</option>
   <option value="MY">Malaysia</option>
   <option value="SG">Singapore</option>
</select>

users.jsp

<%@taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<html>
<head>
    <title>Spring MVC Form Handling</title>
</head>
<body>

<h2>Submitted User Information</h2>
   <table>
      <tr>
         <td>Username</td>
         <td>${username}</td>
      </tr>
      <tr>
         <td>Password</td>
         <td>${password}</td>
      </tr>
      <tr>
         <td>Address</td>
         <td>${address}</td>
      </tr>
      <tr>
         <td>Subscribed to Newsletter</td>
         <td>${receivePaper}</td>
      </tr>
      <tr>
         <td>Favorite Web Frameworks</td>
         <td> <% String[] favoriteFrameworks = (String[])request.getAttribute("favoriteFrameworks");
            for(String framework: favoriteFrameworks) {
               out.println(framework);
            }
         %></td>
      </tr>
      <tr>
         <td>Gender</td>
         <td>${(gender=="M"? "Male" : "Female")}</td>
      </tr>
      <tr>
         <td>Favourite Number</td>
         <td>${favoriteNumber}</td>
      </tr>
      <tr>
         <td>Country</td>
         <td>${country}</td>
      </tr>
   </table>
</body>
</html>

完成创建源文件和配置文件后，导出应用程序。右键单击应用程序并使用Export->WAR File选项，并将您的HelloWeb.war文件保存在Tomcat的webapps文件夹中。

现在启动您的Tomcat服务器，并确保您可以使用标准浏览器从webapps文件夹访问其他网页。现在尝试URL http://localhost:8080/HelloWeb/user，如果您的Spring Web应用程序的一切都很好，您应该会看到以下结果：

提交所需信息后，点击提交按钮提交表单。如果您的Spring Web应用程序的一切都很好，您应该会看到以下结果：

Maven示例：

https://github.com/easonjim/5_java_example/tree/master/springmvc/tutorialspoint/test11