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Servlet转发到jsp

jsp servlets

Servlet转发到jsp,jsp,servlets,requestdispatcher,Jsp,Servlets,Requestdispatcher,我有一个servlet“ShowEvents”，我正试图重定向到WebContent文件夹中的jsp页面“EventsOfClub.jsp”。我正在使用Eclipse。但当我做前锋时，什么也没发生。我知道这是一个常见的错误，但我在这里浏览了很多问题，找不到正确的资源路径（我认为这就是问题所在）。请帮忙 表演活动： request.getRequestDispatcher("EventsOfClub.jsp").forward(request, response); 编辑：当用户登录时，我重定向

我有一个servlet“ShowEvents”，我正试图重定向到WebContent文件夹中的jsp页面“EventsOfClub.jsp”。我正在使用Eclipse。但当我做前锋时，什么也没发生。我知道这是一个常见的错误，但我在这里浏览了很多问题，找不到正确的资源路径（我认为这就是问题所在）。请帮忙

表演活动：

request.getRequestDispatcher("EventsOfClub.jsp").forward(request, response);
编辑：当用户登录时，我重定向（而不是转发）到ShowEvents servlet，如下所示：

response.sendRedirect("ShowEvents");
然后从ShowEvents转发到“EventsOfClub.jsp”，如我前面所说。我以为问题是我没有转发。但现在当我从登录转发到ShowEvents时

request.getRequestDispatcher("ShowEvents").forward(request, response);
我遇到了同样的问题，也就是说，它停留在登录状态，并显示一个空白页面。（之前，ShowEvents显示的是空白页）

编辑： 堆栈跟踪：

SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at org.apache.jsp.EventsOfClub_jsp._jspService(EventsOfClub_jsp.java:116)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at ShowEvents.doPost(ShowEvents.java:82)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
    at Login.doPost(Login.java:88)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
登录servlet

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

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

/**
 * Servlet implementation class Login
 */
@WebServlet(description = "Enter credentials", urlPatterns = { "/Login" })
public class Login extends HttpServlet 
{
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Login() 
    {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {   }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    //POST "localhost:8080/login"
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
        String name = (String) request.getParameter("username");
        String pass = (String) request.getParameter("password");

        Connection conn = null;
        String p="";

        try
        {
            Class.forName("org.postgresql.Driver");
            conn = DriverManager.getConnection("jdbc:postgresql://localhost:6666/Festeria", "postgres", "darthvedarvyas");

            HttpSession session = request.getSession();
            session.setAttribute("connection", conn);
            session.setAttribute("uname", name);

            Statement stmt = null;
            stmt = conn.createStatement();

                    //some DB code

            RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(redirect);
            dispatcher.forward(request,response);
        }
        catch(Exception e)
        {
            e.printStackTrace();
            String msg = "Oops! An error has occured! <br> Please try again.";
            request.getSession().setAttribute("msg", msg);
            response.sendRedirect("Error.jsp");
        }
    }
}

import java.io.IOException；
导入java.sql.Connection；
导入java.sql.DriverManager；
导入java.sql.ResultSet；
导入java.sql.Statement；
导入javax.servlet.RequestDispatcher；
导入javax.servlet.ServletException；
导入javax.servlet.annotation.WebServlet；
导入javax.servlet.http.HttpServlet；
导入javax.servlet.http.HttpServletRequest；
导入javax.servlet.http.HttpServletResponse；
导入javax.servlet.http.HttpSession；
/**
*Servlet实现类登录
*/
@WebServlet（description=“Enter credentials”，urlPatterns={”/Login“}）
公共类登录扩展了HttpServlet
{
私有静态最终长serialVersionUID=1L；
/**
*@参见HttpServlet#HttpServlet（）
*/
公共登录（）
{
超级（）；
//TODO自动生成的构造函数存根
}
/**
*@参见HttpServlet#doGet（HttpServletRequest请求，HttpServletResponse响应）
*/
受保护的void doGet（HttpServletRequest请求，HttpServletResponse响应）抛出ServletException，IOException
{   }
/**
*@请参阅HttpServlet#doPost（HttpServletRequest请求，HttpServletResponse响应）
*/
//发布“本地主机：8080/登录”
受保护的void doPost（HttpServletRequest请求、HttpServletResponse响应）引发ServletException、IOException
{
字符串名称=（字符串）请求.getParameter（“用户名”）；
String pass=（String）request.getParameter（“密码”）；
连接conn=null；
字符串p=“”；
尝试
{
Class.forName（“org.postgresql.Driver”）；
conn=DriverManager.getConnection（“jdbc:postgresql://localhost:6666/Festeria","博士后","达特维达维亚",；
HttpSession session=request.getSession（）；
session.setAttribute（“连接”，conn）；
session.setAttribute（“uname”，名称）；
语句stmt=null；
stmt=conn.createStatement（）；
//一些数据库代码
RequestDispatcher dispatcher=getServletContext（）.getRequestDispatcher（重定向）；
转发（请求、响应）；
}
捕获（例外e）
{
e、 printStackTrace（）；
String msg=“哎呀！发生错误！
请重试。”；
request.getSession（）.setAttribute（“msg”，msg）；
sendRedirect（“Error.jsp”）；
}
}
}
试试这个代码片段

class ShowEvents{
      //----
      doGet(HttpServletRequest request, HttpServletResponse response){
      doPost(request, response);
      }

      doPost(HttpServletRequest request, HttpServletResponse response){
      request.getRequestDispatcher(request.getContextPath()+"/EventsOfClub.jsp")
                                      .forward(request, response);
      }

}
嘿，达斯·韦达尔

我为您制作了一个非常简单的演示：

这是Servlet

package servlets;

import java.io.IOException;
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 EventsOfClubServlet
 */
@WebServlet(name = "events", urlPatterns = { "/events" })
public class EventsOfClubServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public EventsOfClubServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html; charset=UTF-8");
        request.getRequestDispatcher("EventsOfClub.jsp").forward(request, response);
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

}
登录Servlet

package servlets;

import java.io.IOException;

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 LoginServlet
 */
@WebServlet(name = "login", urlPatterns = { "/login" })
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userName = request.getParameter("username");
        String password = request.getParameter("password");

        if((userName != null && userName.equalsIgnoreCase("demo")) && (password != null && password.equalsIgnoreCase("123456"))) {
            response.sendRedirect("events");
        } else {
            request.getRequestDispatcher("login.jsp").forward(request, response);
        }

    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

}
Login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="login" method="post">
        <label>Username: </label>
        <input type="text" name="username"/></br>
        <label>Password:&nbsp;</label>
        <input type="text" name="password"/></br>
        <input type="submit" value="Login">

    </form>
</body>
</html>


在此处插入标题
用户名：


密码：
JSP

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h1>EventsOfClub.jsp</h1>
</body>
</html>


在此处插入标题
EventsOfClub.jsp

这只是说找不到资源。我不认为在这里添加上下文路径有帮助。我之前注意到/丢失了。即使使用/it也无法工作，因为已经添加了上下文路径。问题出在别处。你试过调试你的servlet吗？做一些System.out.println（“”）；getRequestDispatcher（…）并检查它是否在控制台中打印。若问题仍然存在，那个么当我转发时，问题可能在web.xml或eclipse.NullPointerException中。它发生在登录和ShowEvents上。我已经发布了堆栈跟踪。请帮助能否发布您的web.xml？仍然存在相同的问题：servlet只是停留在ShowEvents上。您在浏览器中调用哪个URI？我正在调用Login，这很好。一旦我转发到ShowEvents，它将停留在Lgin并给出NullPointerException您是否可以更新您的请求并添加ShowEvents Servlet和jsp代码以及login.jsp和/或login Servlet，肯定有错误。show
EventsOfClub.jsp
以及您在
ShowEvents.java
第82行的代码是什么？