JDBCInitServlet.java
codice:
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class JDBCInitServlet extends SimpleInitServlet {
protected Connection conn = null;


@Override
public void init(ServletConfig config) throws ServletException {
    super.init(config);
    try {
    // load JDBC driver
         Class.forName(mydriver).newInstance(); 
         conn = DriverManager.getConnection(myurl, myuserID, mypassword);
         System.out.println("Connection successful..");
    }
    catch (SQLException se) 
    { System.out.println(se);}
    catch (Exception e) { e.printStackTrace(); }
}


public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

    res.setContentType("TEXT/HTML");
    PrintWriter out = res.getWriter();
    out.println("<HTML>");  
    out.println("<TITLE>JDBC Init Connection</TITLE>");
    out.println("<BODY>");
    try { 
       executeSQL(out); 
    }
    catch (SQLException se) { se.printStackTrace(); }
    out.println("</BODY></HTML>");
    out.close();
   } 

public void executeSQL(PrintWriter out) throws SQLException{

    Statement stmt = conn.createStatement();

    String sql = "SELECT * FROM DEPARTMENT";
    stmt.executeQuery(sql);
    ResultSet rs = stmt.getResultSet();
    int count = 1;
    while (rs.next()) {
        out.println(""+rs.getString("DEPTNAME")+"
<BLOCKQUOTE>");
        String sql2 = "SELECT * FROM EMPLOYEE WHERE WORKDEPT = '" +
        rs.getString("DEPTNO") + "'";
        Statement stmt2 = conn.createStatement();
        stmt2.executeQuery(sql2);
        ResultSet rs2 = stmt2.getResultSet();
        while(rs2.next()) {
            out.println(rs2.getString("FIRSTNME") + " " +
            rs2.getString("LASTNAME") + "
");
        }
        out.println("</BLOCKQUOTE>");
    }
  }

}

codice:
type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

java.lang.NullPointerException
	JDBCInitServlet.executeSQL(JDBCInitServlet.java:44)
	JDBCInitServlet.doGet(JDBCInitServlet.java:36)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	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/7.0.22 logs.