表单<form>用于搜集不同类型的用户输入。可以轻松地将一个HTML表单从一个Servlet发送到浏览器，当用户提交表单时，在表单元素中输入的值就会被当做请求参数发送到服务器。
request.getParameter(name) 中的name指的是表单中元素的name属性的值
HTML输入域（文本域、隐藏域、密码域）或者文本区的值，会被当做字符串发送到服务器，空的输入域或者文本区会发送空字符串。因此，有输入域名称的，ServletRequest.getParameter(String name)绝对不会返回null
包含多个值的<select>元素，使用ServeltRequest.getParameterValues(name)捕获选中的值，返回一个字符串数组
复选框<input type="checkbox" />，选中的复选框会发送字符串“on”到服务器，未选中的复选框不向服务器发送任何东西，此时ServletRequest.getParameter(name)返回null
单选框<input type="radio" />，将被选中按钮的值（即value属性的值）发送到服务器，若没有选中任何按钮，将没有内容发送到服务器，此时Servletrequest.getParameter(name)返回null
如果同一个表单包含多个输入同名的元素（即name属性的值相同），那么所有值都会被提交，并且必须利用Servlet.getParameterValues(name)来捕获它们并返回一个字符串数组。若使用Servler.getParameter(name)将只会返回最后一个值。
package app01b; import java.io.IOException; import java.io.PrintWriter; import java.util.Enumeration; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class FormServlet */ @WebServlet(name = "FormServlet", urlPatterns = {"/form"}) public class FormServlet extends HttpServlet { private static final long serialVersionUID = 1L; private static final String TITLE = "Order Form"; public FormServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter writer = response.getWriter(); writer.println("<html>"); writer.println("<head>"); writer.println("<title>" + TITLE + "</title>"); writer.println("</head>"); writer.println("<body>"); writer.println("<h1>" + TITLE + "</h1>"); writer.println("<form method='post'>"); writer.println("<table>"); writer.println("<tr>"); writer.println("<td>Name:</td>"); writer.println("<td><input type='text' name='name' /></td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Address:</td>"); writer.println("<td><textarea name='address' cols='40' rows='5'></textarea></td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Country:</td>"); writer.println("<td>"); writer.println("<select name='country'>"); writer.println("<option>United States</option>"); writer.println("<option>Canada</option>"); writer.println("</select>"); writer.println("</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Delivery Method:</td>"); writer.println("<td>"); writer.println("<input type='radio' name='deliveryMethod' value='First Class' />First Class"); // 将被选中按钮的值（即value属性的值）发送到服务器，若没有选中任何按钮，将没有内容发送到服务器，此时Servletrequest.getParameter(name)返回null writer.println("<input type='radio' name='deliveryMethod' value='Second Class' />Second Class"); writer.println("</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Shipping Instructions:</td>"); writer.println("<td><textarea name='instructions' cols='40' rows='5'></textarea></td>"); // 如果同一个表单包含多个输入同名的元素（即name属性的值相同），那么所有值都会被提交，并且必须利用Servlet.getParameterValues(name)来捕获它们并返回一个字符串数组。 writer.println("</tr>"); writer.println("<tr>"); writer.println("<td> </td>"); writer.println("<td><textarea name = 'instructions' cols='40' rows='5'></textarea></td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Please send me the leatest product catalog:</td>"); writer.println("<td><input type='checkbox' name='catalogRequest' /></td>"); // 若选中，发送字符串“on”到服务器;若未选中，不向服务器发送任何东西，此时ServletRequest.getParameter(name)返回null writer.println("</tr>"); writer.println("<tr>"); writer.println("<td> </td>"); writer.println("<td><input type='reset' /><input type='submit' /></td>"); writer.println("</tr>"); writer.println("</table>"); writer.println("</form>"); writer.println("</body>"); writer.println("</html>"); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter writer = response.getWriter(); writer.println("<html>"); writer.println("<head>"); writer.println("<title>" + TITLE + "</title>"); writer.println("</head>"); writer.println("<body>"); writer.println("<h1>" + TITLE + "</h1>"); writer.println("<table>"); writer.println("<tr>"); writer.println("<td>Name:</td>"); writer.println("<td>" + request.getParameter("name") + "</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Address:</td>"); writer.println("<td>" + request.getParameter("address") + "</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Country:</td>"); writer.println("<td>" + request.getParameter("country") + "</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Shipping Instructions:</td>"); writer.println("<td>"); String[] instructions = request.getParameterValues("instruction"); if(instructions != null) { for(String instruction : instructions) { writer.println(instruction + "<br />"); } } writer.println("</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Delivery Method:</td>"); writer.println("<td>" + request.getParameter("deliveryMethod") + "</td>"); writer.println("</tr>"); writer.println("<tr>"); writer.println("<td>Catalog Request:</td>"); writer.println("<td>"); if(request.getParameter("catalogRequest") == null) { writer.println("No"); }else { writer.println("Yes"); } writer.println("</td>"); writer.println("</tr>"); writer.println("</table>"); writer.println("<div style='border:1px solid #ddd; margin-top:40px; font-size:90%'>"); writer.println("Debug Info<br />"); Enumeration<String> parameters = request.getParameterNames(); while(parameters.hasMoreElements()) { String parameterName = parameters.nextElement(); writer.println(parameterName + ": "); String[] parameterValues = request.getParameterValues(parameterName); for(String parameterValue : parameterValues) { writer.println(parameterValue + "<br />"); } } writer.println("</div>"); writer.println("</body>"); writer.println("</html>"); } }
Servlet中写的html代码(doGet()方法中的)。通过浏览器查看
Servlet中写的html代码(doPost()方法中的)
