Question

当我尝试点击我的jsp文件中的按钮时，我的许多servlet之一出现了一个奇怪的错误。关于HTTP状态404和Java Servlet的其他帖子似乎与我遇到的任何内容都没有关系。

HTTP状态404 - 未找到
类型状态报告
消息 / ProjectName / pages / LogoutServlet
说明原始服务器未找到目标资源的当前表示形式，或者不愿透露该目标资源是否存在。

注意：点击按钮后，控制台中没有出现警告或异常。

这是一个在Apache Tomcat v9.0上运行的动态Web项目。

JSP文件（名称：loginSuccess.jsp）

<body>
    <%
        String user = null;
        if(session.getAttribute("user") == null){
            response.sendRedirect("pages/index.jsp");
        } else {
            user = (String) session.getAttribute("user");
        }
        String userName = null;
        String sessionID = null;
        Cookie[] cookies = request.getCookies();
        if(cookies !=null) {
            for(Cookie cookie : cookies){
                if(cookie.getName().equals("user")) {
                    userName = cookie.getValue();
                }
                if(cookie.getName().equals("JSESSIONID")) {
                    sessionID = cookie.getValue();
                }
            }
        } else {
            sessionID = session.getId();
        }
    %>

    <h3>Hi <%=userName %>, Login successful. Your Session ID=<%=sessionID %></h3>

    <br>

    <form action="LogoutServlet" method="post">
        <input type="submit" value="Logout" >
    </form>
</body>

上面JSP底部的表单给出了错误。

Java Servlet（名称：LogoutServlet.java）

package com.main;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet("/LogoutServlet")
public class LogoutServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        Cookie[] cookies = request.getCookies();
        if(cookies != null){
        for(Cookie cookie : cookies){
            if(cookie.getName().equals("JSESSIONID")){
                System.out.println("JSESSIONID="+cookie.getValue());
            }
            cookie.setMaxAge(0);
            response.addCookie(cookie);
        }
        }
        //invalidate the session if exists
        HttpSession session = request.getSession(false);
        System.out.println("User="+session.getAttribute("user"));
        if(session != null){
            session.invalidate();
        }
        response.sendRedirect("pages/index.jsp");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

}

请注意，我使用 @WebServlet 注释声明servlet，而不是在web.xml文件中添加servlet和servlet映射。我在这个应用程序中有大约20个其他servlet具有类似的设置。这个servlet是我遇到这个问题的唯一一个。

当我在调试模式下运行时，应用程序永远不会到达LogoutServlet。

Java Servlet（名称：LoginServlet.java） *这是我的servlet，引导用户访问loginSuccess.jsp

package com.main;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        Connection con = null;
        boolean validated = false;

        response.setContentType("text/html");

        String user = request.getParameter("user");
        String pwd = request.getParameter("pwd");

        try {

            Class.forName("com.mysql.jdbc.Driver"); 

            String url = "jdbc:mysql://localhost:3306/?autoReconnect=true&useSSL=false&user=root";
            Properties dbInfo = new Properties();
            dbInfo.put("user", "root");
            dbInfo.put("password", "root");

            con = DriverManager.getConnection(url, dbInfo);

            String sql = "SELECT uname, pword FROM bankofme.accounts";

            Statement stmt = con.createStatement(); 
            ResultSet rs = stmt.executeQuery(sql);

            while(rs.next()) {
                if(user.equals(rs.getString("uname")) && pwd.equals(rs.getString("pword"))) {
                    validated = true;
                }

            }
            rs.close();

        } catch(Exception e) {
            e.printStackTrace();
        } 

        if(validated) {
            HttpSession session = request.getSession();
            session.setAttribute("user", user);
            session.setMaxInactiveInterval(1800);
            Cookie userName = new Cookie("user", user);
            userName.setMaxAge(1800);
            response.addCookie(userName);

            String encodedURL = response.encodeRedirectUrl("pages/loginSuccess.jsp");
            response.sendRedirect(encodedURL);
        }else{
            RequestDispatcher rd = getServletContext().getRequestDispatcher("pages/index.jsp");
            PrintWriter out= response.getWriter();
            out.println("<font color=red>Either user name or password is wrong.</font>");
            rd.include(request, response);
            out.close();
        }
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

JSP文件（名称：index.jsp）

<body>
    <div id="header">
        <form action="LoginServlet" method="post">
            Name: <input type="text" name="user"><br>
            Password: <input type="password" name="pwd"><br>
            <input type="submit" value="login">
        </form>
    </div><!-- end of header -->
</body>

Java Servlet导致HTTP状态404

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