Question

我基本上已经开始大脑锁定了，在用户点击提交后，它转到一个空白页面甚至没有到达servlet。我放了一个System.out.println来测试它是否到达servlet但它没有。这是web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
    <servlet>
        <servlet-name>servlet03</servlet-name>
        <servlet-class>servlets.Week01_03</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>servlet03</servlet-name>
        <url-pattern>/week01_03servlet</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
    </welcome-file-list>
</web-app>

这是servlet

package servlets;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class Week01_03 extends HttpServlet
{
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        System.out.println("Hello");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String userString = request.getParameter("userString");
        out.close();

        char[] vowel = {'a', 'e', 'i', 'o', 'u'};
        int[] count = {0, 0, 0, 0, 0};

        for (int i = 0; i < userString.length(); i++)
        {
            switch (userString.charAt(i))
            {
                case 'a':
                case 'A':
                    count[0]++;
                    break;
                case 'e':
                case 'E':
                    count[1]++;
                    break;
                case 'i':
                case 'I':
                    count[2]++;
                    break;
                case 'o':
                case 'O':
                    count[3]++;
                    break;
                case 'u':
                case 'U':
                    count[4]++;
                    break;
                default:
                    break;
            }
        }

        try
        {
            out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet Week01_03</title>");
            out.println("<link rel=\"stylesheet\" type=\"text/css\" href=\"Week01_02.css\">");
            out.println("</head>");
            out.println("<body>");
            out.println("<h1>Servlet Week 01, Exercise 03</h1>");
            out.println("<p class=\"inline\">You typed: '<pre class=\"inline\">" +
                        userString + "</pre>'</p>");
            out.println("<h3>Vowel usage:</h3>");
            out.println("<table>");
            for (int i = 0; i < vowel.length; i++)
            {
                out.println("<tr" + (i%2==0 ? " class=\"shaded\"" : "") + ">" +
                            "<td>'" + vowel[i] +
                            "'</td><td>" + count[i] +
                            "</td></tr>");
            }

            out.println("</table>");
            out.println("</body>");
            out.println("</html>");
        }
        finally
        {
            out.close();
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws javax.servlet.ServletException
     * @throws java.io.IOException
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        processRequest(request, response);
    }

    /** 
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws javax.servlet.ServletException
     * @throws java.io.IOException
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        processRequest(request, response);
    }

    /** 
     * Returns a short description of the servlet.
     */
    public String getServletInfo()
    {
        return "Short description";
    }// </editor-fold>
}

这是html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <title>Week 01, Exercise 03</title>
        <link rel="stylesheet" type="text/css" href="Week01_03.css">
    </head>
    <body>
        <h1>Week 01, Exercise 03</h1>
        <form action="week01_03servlet" method="post">
            <p>Type some text in the box:
            <input type="text" name="userString"></p>

            <p>and then click the button, 
                and I'll tell you the frequency of vowel usage:
            <input type="submit" value="Submit"></p>
        </form>
    </body>
</html>

感谢您的回复。

Answer 1

这个servlet不起作用的原因是因为out.close()方法开头的processRequest()指令。

System.out.println("Hello");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String userString = request.getParameter("userString");
**out.close();**

它过早地关闭了用于向客户端发送响应的PrintWriter。因此，客户端仅获得HTTP header content-type: "text/html;charset=UTF-8"的响应，但空体。

Answer 2

我同意Philippe G的观点，这个问题很可能过早了。关闭（）

您之前已经向控制台打印了一条消息，但可能看不到它。由于日志配置的原因，输出可能不是您所期望的，并且System.out可能会被缓冲，直到一段时间后才会被写出。

您通常应该将此类system.out.println切换为使用System.err.println，并确保输出不会从某个地方发送到日志文件，或者被容器完全丢弃

Answer 3

在doPost末尾使用重定向。

response.sendRedirect("/yourpage");

按钮提交后的Java Servlet空白页

3 个答案: