错误信息：type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception java.lang.NullPointerException
com.dvd.view.ListLibraryServlet.doGet(ListLibraryServlet.java:87)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.14 logs.
--------------------------------------------------------------------------------源代码：
ListLibraryServlet.javapackage com.dvd.view;import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import java.util.Iterator;
//import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.dvd.model.DVDItem;
import javax.servlet.ServletContext;public class ListLibraryServlet extends HttpServlet { /**
* Constructor of the object.
*/
public ListLibraryServlet() {
super();
} /**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
} /**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
@SuppressWarnings("unchecked")
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//List dvds = new ArrayList();
//Create the set of dvds
//dvds.add(new DVDItem("Star Wars Episode I","1999","Sci-Fi"));
//dvds.add(new DVDItem("Star Wars","1977","Sci-Fi"));
//Set page title
String pageTitle ="ListLibraryServlet";
//Retrieve the list of dvdItems from the context-scope
ServletContext context = getServletContext();
List dvdList = (List)context.getAttribute("dvdList");
//Specify the content type is HTML
response.setContentType("text/html");
PrintWriter out = response.getWriter();
//Generate the HTML response
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>"+pageTitle+"</TITLE></HEAD>");
out.println(" <BODY bgcolor='white'>");
//Generate page heading
out.print("<!--Page Heading-->");
out.print("<table border='0' cellpadding='3'cellspacing='1'width='400'>");
out.println("<tr bgcolor='#ccccff'");
out.println("<td align='center'><font size='5'>ListLibraryServlet</font></td>");
out.println("</tr>");
out.println("</table>");
//Generate main body
out.println("<p>");
int Size = 0;
//if(dvdList.size() != 0){ Size =dvdList.size();}
out.println("You currently have <font color='red' size='3'><b>"+Size+"</b></font> DVDs in your collection:");
out.println("</p>");
out.println("<table cellpadding='3' cellspacing='1'width='400'>");
out.println("<tr bgcolor='#ccccff'>");
out.println("<td align='left'>Title</td>");
out.println("<td align='center'>Year</td>");
out.println("<td align='center'>Genre</td>");
out.println("</tr>");
Iterator items = dvdList.iterator();
while(items.hasNext()){
DVDItem item = (DVDItem)items.next();
out.println("<tr>");
out.println("<td>"+item.getTitle()+"</td>");
out.println("<td align='center'>"+item.getYear()+"</td>");
out.println("<td align='center'>"+item.getGenre()+"</td>");
out.println("</tr>");
}
out.println("</table>");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
} /**
* The doPost method of theservlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
} /**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}}
InitializeLibrary.java
package com.dvd.web;import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.BufferedReader;import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;import com.dvd.model.DVDItem;
import java.util.List;
import java.util.LinkedList;public class InitializeLibrary implements ServletContextListener {
@SuppressWarnings("unchecked")
public void contextInitialized(ServletContextEvent event){
ServletContext context = event.getServletContext();
List dvdList = new LinkedList();
String dvdsFile = context.getInitParameter("dvd_file");
InputStream is = null;
BufferedReader reader = null;
try{
is = context.getResourceAsStream(dvdsFile);
if(is != null){
reader = new BufferedReader(new InputStreamReader(is));
}
String record ;
//Read every record (one per line)
while((record = reader.readLine().toString()) != null){
String [] fields = record.split("\t");
//Extract the data fields for the record
String title = fields[0];
String year =fields[1];
String genre = fields[2];
//Add the new DVD Item to the list
DVDItem item = new DVDItem(title,year,genre);
dvdList.add(item);
}
context.setAttribute("dvdList", dvdList);
context.log("The DVD list has been loaded.");
}catch(Exception e){
context.log("Exception occured while proccessing the dvdsFile.",e);
}finally{
if(is != null){
try{is.close();}catch(Exception e){}
}
if(reader !=null){
try {reader.close();}catch(Exception e){}
}
}
}
public void contextDestroyed(ServletContextEvent event){ }
}
com.dvd.view.ListLibraryServlet.doGet(ListLibraryServlet.java:87)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.14 logs.
--------------------------------------------------------------------------------源代码：
ListLibraryServlet.javapackage com.dvd.view;import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import java.util.Iterator;
//import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.dvd.model.DVDItem;
import javax.servlet.ServletContext;public class ListLibraryServlet extends HttpServlet { /**
* Constructor of the object.
*/
public ListLibraryServlet() {
super();
} /**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
} /**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
@SuppressWarnings("unchecked")
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//List dvds = new ArrayList();
//Create the set of dvds
//dvds.add(new DVDItem("Star Wars Episode I","1999","Sci-Fi"));
//dvds.add(new DVDItem("Star Wars","1977","Sci-Fi"));
//Set page title
String pageTitle ="ListLibraryServlet";
//Retrieve the list of dvdItems from the context-scope
ServletContext context = getServletContext();
List dvdList = (List)context.getAttribute("dvdList");
//Specify the content type is HTML
response.setContentType("text/html");
PrintWriter out = response.getWriter();
//Generate the HTML response
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>"+pageTitle+"</TITLE></HEAD>");
out.println(" <BODY bgcolor='white'>");
//Generate page heading
out.print("<!--Page Heading-->");
out.print("<table border='0' cellpadding='3'cellspacing='1'width='400'>");
out.println("<tr bgcolor='#ccccff'");
out.println("<td align='center'><font size='5'>ListLibraryServlet</font></td>");
out.println("</tr>");
out.println("</table>");
//Generate main body
out.println("<p>");
int Size = 0;
//if(dvdList.size() != 0){ Size =dvdList.size();}
out.println("You currently have <font color='red' size='3'><b>"+Size+"</b></font> DVDs in your collection:");
out.println("</p>");
out.println("<table cellpadding='3' cellspacing='1'width='400'>");
out.println("<tr bgcolor='#ccccff'>");
out.println("<td align='left'>Title</td>");
out.println("<td align='center'>Year</td>");
out.println("<td align='center'>Genre</td>");
out.println("</tr>");
Iterator items = dvdList.iterator();
while(items.hasNext()){
DVDItem item = (DVDItem)items.next();
out.println("<tr>");
out.println("<td>"+item.getTitle()+"</td>");
out.println("<td align='center'>"+item.getYear()+"</td>");
out.println("<td align='center'>"+item.getGenre()+"</td>");
out.println("</tr>");
}
out.println("</table>");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
} /**
* The doPost method of theservlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
} /**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}}
InitializeLibrary.java
package com.dvd.web;import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.BufferedReader;import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;import com.dvd.model.DVDItem;
import java.util.List;
import java.util.LinkedList;public class InitializeLibrary implements ServletContextListener {
@SuppressWarnings("unchecked")
public void contextInitialized(ServletContextEvent event){
ServletContext context = event.getServletContext();
List dvdList = new LinkedList();
String dvdsFile = context.getInitParameter("dvd_file");
InputStream is = null;
BufferedReader reader = null;
try{
is = context.getResourceAsStream(dvdsFile);
if(is != null){
reader = new BufferedReader(new InputStreamReader(is));
}
String record ;
//Read every record (one per line)
while((record = reader.readLine().toString()) != null){
String [] fields = record.split("\t");
//Extract the data fields for the record
String title = fields[0];
String year =fields[1];
String genre = fields[2];
//Add the new DVD Item to the list
DVDItem item = new DVDItem(title,year,genre);
dvdList.add(item);
}
context.setAttribute("dvdList", dvdList);
context.log("The DVD list has been loaded.");
}catch(Exception e){
context.log("Exception occured while proccessing the dvdsFile.",e);
}finally{
if(is != null){
try{is.close();}catch(Exception e){}
}
if(reader !=null){
try {reader.close();}catch(Exception e){}
}
}
}
public void contextDestroyed(ServletContextEvent event){ }
}
AddDVDServlet.javapackage com.dvd.controller;import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletContext;import com.dvd.model.DVDItem;
import java.util.List;
import java.util.ArrayList;public class AddDVDServlet extends HttpServlet { /**
* Constructor of the object.
*/
public AddDVDServlet() {
super();
} /**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
} /**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
@SuppressWarnings("unchecked")
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
List errorMsgs = new ArrayList();
request.setAttribute("errorMsgs", errorMsgs);
try{
//Retrieve form parameters
String titleStr = request.getParameter("title").trim();
String yearStr = request.getParameter("year").trim();
String genreStr = request.getParameter("genre").trim();
String newgenreStr = request.getParameter("newgenre").trim();
if(titleStr.length() == 0){
errorMsgs.add("Please enter the title of DVD Item");
}
int year = -1;
try{
year = Integer.parseInt(yearStr);
}catch(NumberFormatException nfe){
errorMsgs.add("The 'year' field must be a positive integer");
}
//Verify form parameters
if((year != -1)&&((year <2000)||(year>2100))){
errorMsgs.add("The 'year' field must within 2000 to 2100");
}
if(genreStr.equals("unknown")&&newgenreStr.equals("Add new genre")){
errorMsgs.add("Please select a genre Or define the new Genre");
}
if(!(genreStr.equals("unknown"))&&!(newgenreStr.equals("Add new genre"))){
errorMsgs.add("Please just select one genre:genre Or newgenre");
}
//Send the user back to the AddDVD form, if there were errors
if(! errorMsgs.isEmpty()){
RequestDispatcher view
= request.getRequestDispatcher("add_dvd.view");
view.forward(request, response);
}
//Perform business logic
if(genreStr.equals("unknown")){
genreStr = newgenreStr;
}
//Store the new DVD Application in the request-scope
DVDItem dvdItem = new DVDItem(titleStr,yearStr,genreStr);
request.setAttribute("dvdItem", dvdItem);
//Store the new DVD in the dvdList context-scope attribute
ServletContext context = getServletContext();
List dvdList =(List)context.getAttribute("dvdList");
dvdList.add(dvdItem);
//send the success view
RequestDispatcher view
=request.getRequestDispatcher("success.view");
view.forward(request, response);
}catch(Exception e){
errorMsgs.add(e.getMessage());
}
} /**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}}
严重: Exception occured while proccessing the dvdsFile.
java.lang.NullPointerException
at com.dvd.web.InitializeLibrary.contextInitialized(InitializeLibrary.java:36)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3843)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4342)
.......................................
2010-11-24 23:44:37 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextInitialized()
2010-11-24 23:44:37 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextInitialized()
2010-11-24 23:44:38 org.apache.coyote.http11.Http11Protocol start
信息: Starting Coyote HTTP/1.1 on http-8080
2010-11-24 23:44:38 org.apache.jk.common.ChannelSocket init
信息: JK: ajp13 listening on /0.0.0.0:8009
2010-11-24 23:44:38 org.apache.jk.server.JkMain start
信息: Jk running ID=0 time=0/31 config=null
2010-11-24 23:44:38 org.apache.catalina.startup.Catalina start
信息: Server startup in 2916 ms
代码：package com.dvd.web;import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;
import com.dvd.model.DVDItem;
import java.util.List;
import java.util.LinkedList;public class InitializeLibrary implements ServletContextListener {
@SuppressWarnings("unchecked")
public void contextInitialized(ServletContextEvent event){
ServletContext context = event.getServletContext();
List dvdList = new LinkedList();
String dvdsFile = context.getInitParameter("dvd_file");
InputStream is = null;
BufferedReader reader = null;
try{
is = context.getResourceAsStream(dvdsFile);
if(is != null){
reader = new BufferedReader(new InputStreamReader(is));
}
String record ;
//Read every record (one per line)
record = reader.readLine().toString();
while((record = (String)reader.readLine().toString()) != null){ // 这一行就是每次提示报空指针错误的行 真是想不明白啊
String [] fields = record.split("\t");
//Extract the data fields for the record
String title = fields[0];
String year =fields[1];
String genre = fields[2];
//Add the new DVD Item to the list
DVDItem item = new DVDItem(title,year,genre);
dvdList.add(item);
}
context.setAttribute("dvdList", dvdList);
context.log("The DVD list has been loaded.");
}catch(Exception e){
context.log("Exception occured while proccessing the dvdsFile.",e);
}finally{
if(is != null){
try{is.close();}catch(Exception e){}
}
if(reader !=null){
try {reader.close();}catch(Exception e){}
}
}
}
public void contextDestroyed(ServletContextEvent event){ }
}
改成
ServletContext context=request.getServletContext();
或者
ServletContext context=request.getSession().getServletContext();你上面的context肯定是取不到的 绝对是null
只看了第一个页面 估计是这个原因报空指针异常
谢谢各位哈