Need to specify class name in environment or system property

javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file:  java.naming.factory.initial    at javax.naming.spi.NamingManager.getInitialContext(Unknown Source)    at javax.naming.InitialContext.getDefaultInitCtx(Unknown Source)    at javax.naming.InitialContext.getURLOrDefaultInitCtx(Unknown Source)    at javax.naming.InitialContext.lookup(Unknown Source)    at com.hxj.tools.DatabaseConn.getConnetion(DatabaseConn.java:16)    at com.hxj.dao.EmpDAO.getAll(EmpDAO.java:21)    at com.hxj.dao.EmpDAO.main(EmpDAO.java:50)Exception in thread "main" java.lang.NullPointerException    at com.hxj.dao.EmpDAO.getAll(EmpDAO.java:22)    at com.hxj.dao.EmpDAO.main(EmpDAO.java:50)

<resource-ref>    <description>JNDI DataSource Test</description>    <res-ref-name>jdbc/sqlserver</res-ref-name>    <res-type>javax.sql.DataSource</res-type>    <res-auth>Container</res-auth>    <res-sharing-scope>Shareable</res-sharing-scope></resource-ref>

 <Context path="/pools">      <Resource          name="jdbc/sqlserver"          type="javax.sql.DataSource"          driverClassName="com.microsoft.jdbc.sqlserver.SQLServerDriver"          maxIdle="2"          maxWait="5000"          username="sa"          password="1"          url="jdbc:microsoft:sqlserver://localhost;DatabaseName=test"          maxActive="4"/> </Context>

package com.hxj.tools;import java.sql.Connection;import java.sql.SQLException;import javax.naming.InitialContext;import javax.naming.NamingException;import javax.sql.DataSource;public class DatabaseConn {    public static synchronized Connection getConnetion() {        Connection conn = null;        try {            InitialContext ctx = new InitialContext();            DataSource ds = (DataSource) ctx.lookup("java:comp/env/jdbc/sqlserver");            conn = ds.getConnection();        } catch (SQLException e) {            e.printStackTrace();        } catch (NamingException e) {            e.printStackTrace();        }        return conn;    }}

package com.hxj.dao;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.Iterator;import java.util.List;import com.hxj.bean.Emp;import com.hxj.tools.DatabaseConn;public class EmpDAO {    public List<Emp> getAll(){        List<Emp> list =new ArrayList<Emp>();        String sql = "select * from t_emp";        Connection conn = null;        try {            conn = DatabaseConn.getConnetion();            PreparedStatement psmt = conn.prepareStatement(sql);            ResultSet rs = psmt.executeQuery();            while(rs.next()){                Emp emp = new Emp();                emp.setDeptno(rs.getInt("deptno"));                emp.setEmpname(rs.getString("empname"));                emp.setEmpno(rs.getString("empno"));                list.add(emp);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            try {                if(conn!=null)                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        return list;    }        public static void main(String[] args) {        EmpDAO empDAO = new EmpDAO();        List<Emp> list = empDAO.getAll();        for (Iterator iter = list.iterator(); iter.hasNext();) {            Emp element = (Emp) iter.next();            System.out.println(element.getEmpname());        }    }}