请教：: Servlet.service() for servlet jsp threw exception java.lang.NullPointerExce

hhhhhhh_____ 软件开发 2015-08-15 10:46:29

刚我启动浏览器的时候，提示错误：
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.index_jsp._jspService(index_jsp.java:105)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
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:723)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
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:103)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:620)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)
当我把这段代码删了，页面可以正常显示，但是我不知道这段代码哪里出错了，请各位指教

<div class="feature">

			<%

				String info;

				String dt;

				String user;



				List<HashMap<String, Object>> messageList = JDBCOption.query(SQLConstant.getmessage);

				for (int i = 0; i < messageList.size(); i++) {

					HashMap hm = messageList.get(i);

					user = hm.get("author").toString();

					info = hm.get("info").toString();

					dt = hm.get("published").toString();

			%>

			<div class="message">

				<h3><%=user %></h3>

				<p><%=info %></p>

				<h3><%=dt %></h3>

			</div>



			<%

				}

			%>

			

		</div>

源代码如下

<%@ page language="java" contentType="text/html; charset=UTF-8"

	pageEncoding="UTF-8"%>

<%@ page import="java.util.List"%>

<%@ page import="java.util.HashMap"%>

<%@page import="com.dedo.BBS.Jdbc.SQLConstant"%>

<%@page import="com.dedo.BBS.Jdbc.JDBCOption"%>



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<!-- DW6 -->

<head>

<!-- Copyright 2005 Macromedia, Inc. All rights reserved. -->

<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />

<title>Untitled Document</title>

<link rel="stylesheet" href="/CSS/common.css" type="text/css" />

<style type="text/css">

<!--

.message {

	padding: 10px;

	float: left;

	height: 200px;

	width: 200px;

	position: relative;

}

-->

</style>

</head>

<!-- The structure of this file is exactly the same as 2col_rightNav.html;

     the only difference between the two is the stylesheet they use -->

<body>

	<jsp:include page="head.jsp" flush="true" />

	<!-- end masthead -->

	<div id="content">

		<div id="breadCrumb">

			<a href="#">所有</a> /正向<a href="#"></a> / <a href="#">反向</a>/

		</div>

		<h2 id="pageName">公告区</h2>

		<div class="feature">//这里有错******

			<%

				String info;

				String dt;

				String user;



				List<HashMap<String, Object>> messageList = JDBCOption.query(SQLConstant.getmessage);

				for (int i = 0; i < messageList.size(); i++) {

					HashMap hm = messageList.get(i);

					user = hm.get("author").toString();

					info = hm.get("info").toString();

					dt = hm.get("published").toString();

			%>

			<div class="message">

				<h3><%=user %></h3>

				<p><%=info %></p>

				<h3><%=dt %></h3>

			</div>



			<%

				}

			%>

			

		</div>

	</div>

	<!--end content -->

	<div id="navBar">

		<div id="search">

			<form action="/SubMessage" method="post">

				<label>输入发布内容</label>

				<textarea name="message" cols="26" rows="20"></textarea>

				<input name="goButton" type="submit" value="发布" />

			</form>

		</div>

		<div id="headlines">

			<h3>小白</h3>

			<p> </p>

		</div>

	</div>

	<!--end navbar -->

	<jsp:include page="foot.jsp" flush="true" />

	<br />

</body>

</html>

package com.dedo.BBS.Servlet;



import java.io.IOException;

import java.io.PrintWriter;

import java.sql.Timestamp;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import com.dedo.BBS.Jdbc.JDBCOption;

import com.dedo.BBS.Jdbc.SQLConstant;

import com.dedo.BBS.Tool.Common;







/**

 * Servlet implementation class SubMessage

 */

public class SubMessage extends HttpServlet {

	private static final long serialVersionUID = 1L;

       

    /**

     * @see HttpServlet#HttpServlet()

     */

    public SubMessage() {

        super();

        // TODO Auto-generated constructor stub

    }



	/**

	 * @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);

	}

	

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

	{

		String message = request.getParameter("message");

		java.util.Date d = new java.util.Date();

		JDBCOption.update(SQLConstant.addmessage, 1,message,new Timestamp(d.getTime()));

		response.sendRedirect("index.jsp");

	}



}

package com.dedo.BBS.Jdbc;



import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.ResultSetMetaData;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;



import com.dedo.BBS.Tool.Common;



public class JDBCOption {

	private static DBConfig dbconfig = null;



	static {//连接数据库

		dbconfig = new DBConfig();

		try {

			Class.forName(dbconfig.getDriver());

		} catch (ClassNotFoundException e) {

			e.printStackTrace();

		}

	}

	/*

	 * 查询操作

	 */

	public static List query(String sql, Object... paramters) {

		List returnValue = new ArrayList();

		ResultSet rs = null;

		Connection conn = null;

		PreparedStatement ps = null;



		try {

			conn = DriverManager.getConnection(dbconfig.getUrl(), dbconfig.getUsername(), dbconfig.getPassword());

			ps = conn.prepareStatement(sql);

			for (int i = 0; i < paramters.length; i++) {

				ps.setObject(i + 1, paramters[i]);

			}

			

			rs = ps.executeQuery();

			

			while (rs.next()) {

				ResultSetMetaData md = rs.getMetaData();

				Map map = new HashMap();

				

				for (int i = 0; i < md.getColumnCount(); i++) {

					map.put(md.getColumnLabel(i + 1), rs.getObject(i + 1));

				}

				returnValue.add(map);

			}



		} catch (SQLException e) {

			e.printStackTrace();

		}finally{

			Common.free(conn, ps, rs);

		}



		return returnValue;

	}

	

		

	

}

...全文

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7 条回复

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daliner6 2016-09-01

原来是我数据库和代码写错了一个字母希望自己以后可以吸取教训 --这个是什么意思，写错一个字母也会导致这样的问题？

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hhhhhhh_____ 2015-08-16

引用 1 楼 libingxin 的回复:

你的hashMap的value类型为object hm.get("author") 有肯能为null 你可以用(String)hm.get("author")

你好，我发现，当我把数据库里面的数据清空时，页面可以正常显示，但是当我提交数据的时候就会提示错误。我很困惑

<form action="/SubMessage" method="post">
				<label>输入发布内容</label>
				<textarea name="message" cols="26" rows="20"></textarea>
				<input name="goButton" type="submit" value="发布" />
			</form>

servlet代码如下：

package com.dedo.BBS.Servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Timestamp;

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

import com.dedo.BBS.Jdbc.JDBCOption;
import com.dedo.BBS.Jdbc.SQLConstant;
import com.dedo.BBS.Tool.Common;



/**
 * Servlet implementation class SubMessage
 */
public class SubMessage extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SubMessage() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @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);
	}
	
	protected void processRequest(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException
	{
		String message = request.getParameter("message");
		java.util.Date d = new java.util.Date();
		JDBCOption.update(SQLConstant.addmessage, 1,message,new Timestamp(d.getTime()));
		response.sendRedirect("index.jsp");
	}

}

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开心的冰屋 2015-08-16

你把toString()去掉就可以了

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hhhhhhh_____ 2015-08-16

原来是我数据库和代码写错了一个字母

希望自己以后可以吸取教训

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hhhhhhh_____ 2015-08-16

引用 4 楼 libingxin 的回复:

你把toString()去掉就可以了

谢谢指教！之后我把数据声明改为了object，并且删除了tosting就解决了问题

Object info;
				Object dt;
				Object user;

				List <HashMap<String, Object>>messageList = JDBCOption.query(SQLConstant.getmessage);
				for (int i = 0; i < messageList.size(); i++) {
					HashMap hm = messageList.get(i);
		
					user = hm.get("author");
					info = hm.get("info");
					dt = hm.get("published");
					System.out.println(user);
					System.out.println(info);
					System.out.println(dt);

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hhhhhhh_____ 2015-08-15

引用 1 楼 libingxin 的回复:

你的hashMap的value类型为object hm.get("author") 有肯能为null 你可以用(String)hm.get("author")

我去试了一下


                                String info;
				String dt;
				String user;

				List <HashMap<String, Object>>messageList = JDBCOption.query(SQLConstant.getmessage);
				for (int i = 0; i < messageList.size(); i++) {
					HashMap hm = (HashMap) messageList.get(i);
					System.out.println(hm.get("info"));
					System.out.println(hm.get("published"));
					System.out.println(hm.get("auther"));
					
					user = (String)hm.get("author").toString();
					info = (String)hm.get("info").toString();
					dt = (String)hm.get("published").toString();
					System.out.println(user);
					System.out.println(info);
					System.out.println(dt);

前面那个println可以输出，说明数据库里面有数据的，但是为什么赋值之后却不能输出呢 nihao 2014-02-02 00:00:00.0 2 八月 15, 2015 11:29:50 下午 org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet jsp threw exception java.lang.NullPointerException at org.apache.jsp.index_jsp._jspService(index_jsp.java:109) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388) 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:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) 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:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:620) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source)

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开心的冰屋 2015-08-15

你的hashMap的value类型为object hm.get("author") 有肯能为null 你可以用(String)hm.get("author")

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