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>