netbean问题

Question

SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
        at org.apache.jsp.userLogin_jsp._jspService(userLogin_jsp.java:93)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        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 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
        at java.lang.Thread.run(Thread.java:722)

Answer 1

空指针
最基本的。
应该是
service中的哪个对象忘了实例化了吧？

Answer 2

网页对应的是
HTTP Status 500 -type Exception reportmessagedescription The server encountered an internal error () that prevented it from fulfilling this request.exceptionorg.apache.jasper.JasperException: An exception occurred processing JSP page /userLogin0.jsp at line 4744:                             if (login.isValidUser()) {
45:                                 session.setAttribute("username", username);
46:                                 if (login.isValidPassword()) {
47:                                     if (ran.equals(random)) {
48:                                         session.setAttribute("userPassword", userpassword);
49:                                         response.sendRedirect("index.jsp");
50:                                     } else {
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
root causejava.lang.NullPointerException
org.apache.jsp.userLogin0_jsp._jspService(userLogin0_jsp.java:105)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.26 logs.
我的第47行怎么错了，找不到原因

Answer 3

              if (ran.equals(random)) {你在页面比较是否相等？估计是random这个字符串没有值，你可以输出测试下。或者用debug

Answer 4

userLogin0.jsp
<%@page import="comj.*"%>
<%@ page language="java" contentType="text/html;charset=utf-8"%>
<%@ page import="java.sql.*"%>
<%--<jsp:useBean id="dbconn" scope="session" class="OpenDB"/>
<jsp:useBean id="login" scope="session" class="login"/>--%>
<html>
    <head>
        <title>管理系统</title>
        <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
    </head>
    <body background="#00FFFF">
        <%
                    String username = request.getParameter("txtloginName");
                    String userpassword = request.getParameter("txtpassword");
                    String confirm = request.getParameter("conFirm");
                    String ran = request.getParameter("yzm");
                    String random = String.valueOf(request.getSession().getAttribute("random"));
                    if (username == "") {
        %>
        <center><font size="5">
                <b>登录失败</b><br><br>
                <b>请不要将用户名省略，谢谢喽！</b><br><br>
                <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1);">
            </font></center>        <%            }
                    if (username != "" && userpassword == "") {
        %>
        <center><font size="5">
                <b>登录失败</b><br><br>
                <b>请不要将密码省略，没有密码可是登不上的哦！</b><br><br>
                <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1)">
            </font></center>
            <%            }
                        if (username != "" && userpassword != "") {
                            System.out.println(username);
                            System.out.println(userpassword);
                            OpenDB dbconn = new OpenDB();
                            Login0 login = new Login0();
                            login.userName = username;
                            login.userPassword = request.getParameter("txtpassword");
                            username = request.getParameter("txtloginName");
                            login.setConnection(dbconn.getConnection());
                            if (login.isValidUser()) {
                                session.setAttribute("username", username);
                                if (login.isValidPassword()) {
                                    if (ran.equals(random)) {
                                        session.setAttribute("userPassword", userpassword);
                                        response.sendRedirect("index.jsp");
                                    } else {
            %>
        <center><font size="5">
                <b>登录失败，请检查您的验证码</b>
            </font></center><br><br>
        <center>
            <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1)">
        </center>
        <%                                            }                                        } else {
        %>
        <center><font size="5">
                <b>登录失败，请检查您的密码</b>
            </font></center><br><br>
        <center>
            <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1)">
        </center>
        <%                             }
                                    } else {
        %>
        <center><font size="5">
                <b>登录失败，没有此用户名</b>
            </font></center><br><br>
        <center>
            <input type="button" name="goback" value="返回" onClick="javascript:window.history.go(-1)">
        </center>
        <%                }
                    }
        %>
    </body>
</html>
Random.jsp
<%@ page contentType="image/jpeg"%>
<%@ page import="java.awt.*,java.awt.image.*"%>
<%@ page import="java.util.*,javax.imageio.*"%>
<%@ page import="java.io.OutputStream"%><%!Color getRandColor(int fc, int bc) {
        Random r = new Random();
        if (fc > 255) {
            fc = 255;
        }
        if (bc > 255) {
            bc = 255;
        }
        int red = fc + r.nextInt(bc - fc);
        int green = fc + r.nextInt(bc - fc);
        int blue = fc + r.nextInt(bc - fc);
        return new Color(red, green, blue);
    }%><%
            try {
                response.setHeader("Parama", "No-cache");
                response.setHeader("Cache-Control", "no-cache");
                response.setDateHeader("Expires", 0);                Random r = new Random();                int width = 60, height = 20;
                BufferedImage pic = new BufferedImage(width, height,
                        BufferedImage.TYPE_INT_RGB);
                OutputStream os = response.getOutputStream();
                Graphics gc = pic.getGraphics();                gc.setColor(getRandColor(200, 250));
                gc.fillRect(0, 0, width, height);                gc.setFont(new Font("Times New Roman", Font.PLAIN, 18));                gc.setColor(getRandColor(160, 200));
                for (int i = 0; i < 200; i++) {
                    int x1 = r.nextInt(width);
                    int y1 = r.nextInt(height);
                    int x2 = r.nextInt(15);
                    int y2 = r.nextInt(15);
                    gc.drawLine(x1, y1, x1 + x2, y1 + y2);
                }                gc.setColor(getRandColor(120, 240));
                for (int i = 0; i < 100; i++) {
                    int x = r.nextInt(width);
                    int y = r.nextInt(height);
                    gc.drawOval(x, y, 0, 0);
                }                String RS = "";
                String rn = "";
                for (int i = 0; i < 4; i++) {
                    rn = String.valueOf(r.nextInt(10));
                    RS += rn;                    gc.setColor(new Color(20 + r.nextInt(110), 20 + r.nextInt(110),
                            20 + r.nextInt(110)));
                    gc.drawString(rn, 13 * i + 6, 16);
                }                session.setAttribute("random", RS);
                gc.dispose();
                ImageIO.write(pic, "jpeg", os);                os.flush();
                os.close();
                os = null;
                response.flushBuffer();
                out.clear();
                out = pageContext.pushBody();
            } catch (IllegalStateException e) {
                System.out.println(e.getMessage());
                e.printStackTrace();
            }
%>