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java - 使用注册用户登录时 Servlet 会崩溃，但注册帐户后自动登录时不会崩溃

转载 作者：行者123 更新时间：2023-12-01 13:12:32 25 4
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这是一个大学实验室。我已经被困了3天了。我正在使用 Google App Engine 和 Java 构建一个图像查看器网站。我制作了一个具有登录功能的网页。在欢迎页面上，用户可以注册帐户或登录。如果我注册一个新帐户，那么没有问题，用户数据将被保存，cookie 将添加到 http 响应中，并且用户将进入下一页，他/她可以上传和查看他们在注册帐户时选择的类别中的图像。但是，如果我尝试以已有帐户的用户身份登录，则应用程序会在成功登录后崩溃并出现 NullPointerException 异常，我无法弄清楚出了什么问题。

注册和登录的过程是相同的，除了保存到数据库和从数据库读取之外。

这是我的欢迎页面:

<%@ page import="com.google.appengine.api.blobstore.BlobstoreServiceFactory" %>
<%@ page import="com.google.appengine.api.blobstore.BlobstoreService" %>
<%@ page import="com.blobtest.UserManager" %>
<%@ page import="com.blobtest.UserDatastore" %>
<%@ page import="com.google.appengine.api.datastore.Entity" %>
<%@ page import="java.util.List" %>
<%
    BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
    UserManager userManager = new UserManager();
    UserDatastore dataStore = new UserDatastore();


        Cookie cookie = null;
        Cookie[] cookies = null;
        cookies = request.getCookies();
        if(cookies != null){
            System.out.println("");
            System.out.println("============ From WELCOME.JSP =================");
            System.out.println("");
            System.out.println("Found Cookies!!");
            for(int i = 0; i < cookies.length; i++){
                cookie = cookies[i];
                System.out.println("");
                System.out.println("Name: " + cookie.getName());
                System.out.println("Value: " + cookie.getValue());
                System.out.println("Domain: " + cookie.getDomain());
            }
            System.out.println("");
            System.out.println("============ From WELCOME.JSP =================");
            System.out.println("");
        }

%>


<html>
    <head>
        <title>Welcome</title>
        <link rel="StyleSheet" type="text/css" href="Style.css" />
    </head>
    <body>

    <h1>Welcome to the Picture Gallery!</h1>
    <p>To log in enter your email and password and press "Login", to register enter your email, the password you want and select a role from the menu and press "Login"</p>
        <form action="usermanager" method="post">
            <label>E-Mail:</label>
            <input name="username" type="text" size="30" maxlength="2048" />
            <label>Password:</label>
            <input name="password" type="password" size="30" maxlength="2048" />
            <label>Role:</label>
            <select name="register_role">
            <%
        List<Entity> registerRoles = dataStore.getRoles();
        for(Entity role : registerRoles){
        out.println("<option>" + role.getProperty("role") + "</option>");
        }
%>
            </select>
            <input type="submit" value="Login">
        </form>

    <h1>Gallery Viewer</h1>
    <p>Select a gallery from the menu below and press "Go" to view it</p>

    <form action="/serve" method="get">
        <select name="role">
<%
        List<Entity> roles = dataStore.getRoles();
        for(Entity role : roles){
        out.println("<option>" + role.getProperty("role") + "</option>");
        }

%>
            </select>
            <input type="submit" value="Go">
        </form>
    </body>
</html>

这是我的 UserManager 类:

package com.blobtest;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.appengine.api.datastore.Entity;

public class UserManager extends HttpServlet {

    /**
     * 
     */
    private static final long serialVersionUID = 8824378069546886214L;
    public final String ROLE_SOLDIER = "soldier";
    public final String ROLE_PROGRAMMER = "programmer";
    public final String ROLE_SINGER = "singer";
    public final String ROLE_FOOTBALLER = "footballer";
    public final String COOKIE_PROPERTY_ROLE = "role";
    public final String COOKIE_PROPERTY_USER = "verifieduser";
    public final String COOKIE_APP_DOMAIN = "ImageViewer.se";
    private UserDatastore datastore;

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

        datastore = new UserDatastore();
        checkCookies(request);
        String email = request.getParameter("username");
        String password = request.getParameter("password");
        String role = request.getParameter("register_role");
        Entity user = datastore.selectUser(email);
        /*
         * If the database returns a user, check the password matches, otherwise
         * register the user
         */
        if (user != null) {

            if (password.equals(user.getProperty("password"))) {

                message("REGISTERED USER FOUND:", true, 0);
                message("user: " + user.getProperty("email") + "; Password: "
                        + user.getProperty("password"), false, 0);
                // request.getSession().setAttribute("loggedInUser", userName);
                Cookie cookie = new Cookie(this.COOKIE_PROPERTY_ROLE, user
                        .getProperty("role").toString());
                message("UserManager: New Cookie created with role: "
                        + user.getProperty("role").toString(), false, 0);
                cookie.setMaxAge(300); // -1 = persist for the duration of the
                                        // session; 0 = remove cookie; value > 0
                                        // = time in seconds.
                response.addCookie(cookie);
                Cookie userCookie = new Cookie(this.COOKIE_PROPERTY_USER, user
                        .getProperty("email").toString());
                message("UserManager: New Cookie created with verifieduser: "
                        + user.getProperty("email").toString(), true, 1);

                userCookie.setMaxAge(300); // -1 = persist for the duration of
                                            // the session; 0 = remove cookie;
                                            // value > 0 = time in seconds.
                response.addCookie(userCookie);
                dispatch(request, response, "/loggedin.jsp");
            } else {
                message("Passwords don't match, invalidating session", true, 0);
                message("", true, 1);
                request.getSession().invalidate(); // need to dispose of cookies
                                                    // here, not currently using
                                                    // sessions
                dispatch(request, response, "/welcome.jsp");
            }
        } else {
            datastore.addUser(email, password, role);
            message("NEW USER ADDED:", true, 0);
            Cookie cookie = new Cookie(this.COOKIE_PROPERTY_ROLE, role);
            message("UserManager: New Cookie created with role: " + role,
                    false, 0);
            cookie.setMaxAge(300); // -1 = persist for the duration of the
                                    // session; 0 = remove cookie; value > 0 =
                                    // time in seconds.
            response.addCookie(cookie);
            Cookie userCookie = new Cookie(this.COOKIE_PROPERTY_USER, email);
            message("UserManager: New Cookie created with verifieduser: "
                    + email, true, 1);

            userCookie.setMaxAge(300); // -1 = persist for the duration of the
                                        // session; 0 = remove cookie; value > 0
                                        // = time in seconds.
            response.addCookie(userCookie);
            dispatch(request, response, "/register.jsp");
        }

    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException {

    }

    protected void dispatch(HttpServletRequest request,
            HttpServletResponse response, String page)
            throws javax.servlet.ServletException, java.io.IOException {
        RequestDispatcher dispatcher = getServletContext()
                .getRequestDispatcher(page);
        dispatcher.forward(request, response);

    }

    private void checkCookies(HttpServletRequest request) {
        Cookie cookie = null;
        Cookie[] cookies = null;
        cookies = request.getCookies();
        if (cookies != null) {
            message("Found Cookies!!", true, 0);
            for (int i = 0; i < cookies.length; i++) {
                cookie = cookies[i];
                message("Name: " + cookie.getName(), false, 0);
                message("Value: " + cookie.getValue(), false, 0);
                message("Domain: " + cookie.getDomain(), false, 0);
            }
            message("", true, 1);
        }
    }

    /**
     * Formats the message and message wrapper
     * 
     * @param message
     *            The message to print
     * @param includeWrapper
     *            true to include header/footer labels
     * @param position
     *            if includeWrapper is true, then set 0 for header 1 for footer,
     *            otherwise set 0.
     */
    private void message(String message, boolean includeWrapper, int position) {

        if (includeWrapper) {

            if (position == 0) {
                System.out.println("");
                System.out
                        .println("==========From USERMANAGER===================");
                System.out.println("");
                System.out.println(message);

            } else {
                System.out.println(message);
                System.out.println("");
                System.out
                        .println("========== From USERMANAGER ===================");
                System.out.println("");
            }
        } else {
            System.out.println(message);

        }
    }

}

我的“登录成功”和“注册成功”页面完全相同，它们只是重定向到下面的Uploader.jsp页面:

<%@ page import="com.google.appengine.api.blobstore.BlobstoreServiceFactory" %>
<%@ page import="com.google.appengine.api.blobstore.BlobstoreService" %>
<%@ page import="com.blobtest.UserManager" %>
<%@ page import="com.blobtest.UserDatastore" %>
<%@ page import="com.google.appengine.api.datastore.Entity" %>
<%@ page import="java.util.List" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<% //taglib xmlns:h="http://java.sun.com/jsf/html"prefix="h" %>

<%
    BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
    UserManager userManager = new UserManager();
    UserDatastore dataStore = new UserDatastore();
    Cookie[] cookies = request.getCookies();
    Cookie userCookie = null;
    boolean ok = false;
    for(int i = 0; i < cookies.length; i++){
        if(cookies[i].getName().equals(userManager.COOKIE_PROPERTY_USER)){
            if(cookies[i].getValue() != null){
                ok = true;
            }
        }else if(cookies[i].getName().equals(userManager.COOKIE_PROPERTY_ROLE)){
                userCookie = cookies[i];    
        }
    }

    if(!ok){
        System.out.println("Request failed, number of cookies found: " + cookies.length + ", redirecting to welcome.jsp");
        for(int i = 0; i < cookies.length; i++){
            System.out.println("Name: " + cookies[i].getName() + ", Value: " + cookies[i].getValue());
        }
        RequestDispatcher dispatcher = getServletContext()
                .getRequestDispatcher("/welcome.jsp");
        dispatcher.forward(request, response);
    }
%>

<html>
    <head>
        <title>Upload Test</title>
        <link rel="StyleSheet" type="text/css" href="style.css" />
    </head>
    <body>
        <form action="<%= blobstoreService.createUploadUrl("/upload") %>" method="post" enctype="multipart/form-data">

            <input type="text" name="description">
            <input type="file" name="myFile">
            <input type="submit" value="Submit">
        </form>
    <form action="/usermanager" method="post" enctype="multipart/form-data">

    </form>
            <form action="/serve" method="get">
            <select name="role">
<%
    if(userCookie != null) out.println("<option>" + userCookie.getValue() + "</option>");

%>
            </select>
            <input type="submit" value="Go">
        </form>
        <%
        Cookie cookie2 = null;
        Cookie[] cookies2 = null;
        // Get an array of Cookies associated with this domain
        cookies2 = request.getCookies();
        if( cookies2 != null ){
           out.println("<h2> Found Cookies Name and Value</h2>");
           for (int i = 0; i < cookies.length; i++){
              cookie2 = cookies2[i];
              out.print("Name : " + cookie2.getName( ) + ",  ");
              out.print("Value: " + cookie2.getValue( )+" <br/>");
           }
       }else{
           out.println("<h2>No cookies founds</h2>");
       }
        %>
        <a href="/logout.jsp">Click to Log Out</a>
    </body>
</html>

上面的页面是应用程序崩溃的地方。如果我尝试使用以前注册的用户登录，则会收到以下错误(包括 UserManager 的一些打印输出):

Retreiving user: paul@email.com, 1234, programmer

==========From USERMANAGER===================

REGISTERED USER FOUND:
user: paul@email.com; Password: 1234
UserManager: New Cookie created with role: programmer
UserManager: New Cookie created with verifieduser: paul@email.com

========== From USERMANAGER ===================

mar 30, 2014 12:53:53 EM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: /uploader.jsp
java.lang.NullPointerException
    at org.apache.jsp.uploader_jsp._jspService(uploader_jsp.java:76)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    at com.google.appengine.tools.development.PrivilegedJspServlet.access$101(PrivilegedJspServlet.java:23)
    at com.google.appengine.tools.development.PrivilegedJspServlet$2.run(PrivilegedJspServlet.java:61)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.google.appengine.tools.development.PrivilegedJspServlet.service(PrivilegedJspServlet.java:58)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:127)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:98)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:487)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)


==========From USERMANAGER===================

NEW USER ADDED:
UserManager: New Cookie created with role: soldier
UserManager: New Cookie created with verifieduser: paul3@email.com

========== From USERMANAGER ===================

mar 30, 2014 12:54:32 EM com.google.appengine.api.datastore.dev.LocalDatastoreService$PersistDatastore persist
INFO: Time to persist datastore: 56 ms

正如您在上面所看到的，添加新用户时我没有收到任何错误，它会按应有的方式进入 uploader.jsp 页面，我可以毫无问题地上传和查看图片。任何指示将不胜感激。

最佳答案

检查cokkies可能是null在你的jsp底部for (int i = 0; i < cookies.length; i++){代码行:

<%
        Cookie cookie2 = null;
        Cookie[] cookies2 = null;
        // Get an array of Cookies associated with this domain
        cookies2 = request.getCookies();
        if( cookies2 != null ){
           out.println("<h2> Found Cookies Name and Value</h2>");
           for (int i = 0; i < cookies.length; i++){ //Here cookies may be null
              cookie2 = cookies2[i];
              out.print("Name : " + cookie2.getName( ) + ",  ");
              out.print("Value: " + cookie2.getValue( )+" <br/>");
           }
       }else{
           out.println("<h2>No cookies founds</h2>");
       }
        %>

这个answer可能会帮助您了解如何使用jSTL在jsp中使用/检索cokkies，您可以避免一些NullPointerException就这样。

<小时/>

另请参阅:

how to avoid java code in jsp

how to use if else in jstl

how to loop in jstl

关于java - 使用注册用户登录时 Servlet 会崩溃，但注册帐户后自动登录时不会崩溃，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22743380/

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