Tomcat ClassNotFoundException for HttpServlet

Question

We are getting a java.lang.ClassNotFoundException: HttpServlet with a JSP project running on the Apache Tomcat server (v5.5) in Eclipse. The lib folder under Web-inf does have the servelt-api jar. And furthermore we have imported the javax.servlet.http.* library. But still we are getting this exception.

package com.bean;

import java.io.*;
import java.util.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class AdminLogin extends HttpServlet{
    ArrayList list=new ArrayList();

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

        try{
        response.setContentType("text/html");       
        PrintWriter out=response.getWriter();    
        String id=request.getParameter("user");
        String pass=request.getParameter("pass");
        System.out.println("ID==================>>"+id+"PASS========>>"+pass);
        if(id.equalsIgnoreCase("admin")&&pass.equalsIgnoreCase("admin"))
                {
                    response.sendRedirect("AdminPage.jsp");                 
                }
                else
                {
                    response.sendRedirect("Failure.html");        
                }           
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }

        }
}

Error Stack Trace:

java.lang.NoClassDefFoundError: HttpServlet
    java.lang.ClassLoader.defineClass1(Native Method)
    java.lang.ClassLoader.defineClassCond(Unknown Source)
    java.lang.ClassLoader.defineClass(Unknown Source)
    java.security.SecureClassLoader.defineClass(Unknown Source)
    org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1847)
    org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:873)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1326)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1205)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
    org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
    org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
    org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
    org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
    org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
    java.lang.Thread.run(Unknown Source)
root cause

java.lang.ClassNotFoundException: HttpServlet
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1359)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1205)
    java.lang.ClassLoader.defineClass1(Native Method)
    java.lang.ClassLoader.defineClassCond(Unknown Source)
    java.lang.ClassLoader.defineClass(Unknown Source)
    java.security.SecureClassLoader.defineClass(Unknown Source)
    org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1847)
    org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:873)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1326)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1205)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
    org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
    org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
    org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
    org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
    org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
    java.lang.Thread.run(Unknown Source)

Web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    <display-name>CarPooling</display-name>
    <servlet>
        <description>
        </description>
        <display-name>AdminLogin</display-name>
        <servlet-name>AdminLogin</servlet-name>
        <servlet-class>com.bean.AdminLogin</servlet-class>
        </servlet>
        <servlet>
 <servlet-name>employee</servlet-name>
 <servlet-class>com.bean.UserLogin</servlet-class>
 </servlet>
    <servlet-mapping>
        <servlet-name>AdminLogin</servlet-name>
        <url-pattern>/demo</url-pattern>
    </servlet-mapping>  
  <servlet-mapping>   
  <servlet-name>employee</servlet-name>
 <url-pattern>/login</url-pattern>                             
 </servlet-mapping>  
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>      
    </welcome-file-list>
</web-app>

project folder structure:

Answer 1

1: Right Click on your Project -> 2: Build path -> 3: Add Libraries -> 4: User Libraries -> 5: click on user libraries -> 6: click on new -> 7: Give an library name you like -> 8: click on "Add External Jars" -> 9: browse and select any of the jar file you need.

but in your case if you need servlet-api.jar it is located at TomcatX.X/lib/*.jar

Consider this solution if you are missing only that .jar file. It is not a best practice at all for the core libraries.

If your PC is properly configured these library files are automatically loaded to your project by eclipse.

Answer 2

The lib folder under Web-inf does have the servelt-api jar.

There is no need to add servlet-api.jar to Classpath. IDE takes care of that.

Check whether you Build Path contains Tomcat libraries.

Right click on Project --> Properties.

Sample Screen