Database access code prob

Question

Hi there, can anyone see if there is anything wrong with the code below. I can see that the variables have values when outputting to dos but I keep getting a NullPointerException. Any ideas why?
Error:
Exception in thread "main" java.lang.NullPointerException
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:130)
at com.javacomponents.DBConnection.getConnection(DBConnection.java:35)
at com.javacomponents.testDBConn.main(testDBConn.java:13)
Press any key to continue . . .
code with static main method:
import java.sql.*;
import java.util.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class testDBConn{
   public static void main(String args[]){
        try{
          Connection connection=DBConnection.getConnection();
          Statement statement = connection.createStatement();
          String query = "select * from users";
          ResultSet rs = statement.executeQuery(query);
          while(rs.next()){
               System.out.println(rs.getString(1));
          statement.close();
          connection.close();
          }catch(SQLException SQLe){
                    System.out.println("SQL Error "+SQLe.getMessage());
}DB Connection class
import java.sql.*;
public class DBConnection {
    private static String username = null;
    private static String password = null;
    private static String dbURL  = null;
    private static String driver = null;
    private static Connection connection = null;
    public static void setUsername (String val) {
  username = val;
    public static void setPassword (String val) {
  password = val;
    public static void setDbURL (String val) {
  dbURL = val;
    public static void setDriver (String val) {
  driver = val;
    System.out.println("driver = "+driver);
public static Connection getConnection () {
  if (connection != null) return connection;
  try {
   Class.forName( driver ); // load the JDBC "driver" class
   connection = DriverManager.getConnection( dbURL, username, password ); // get connection
   return connection;
  } catch ( ClassNotFoundException e ) {
             System.out.println("in ClassNotFoundException");
   return null;
  } catch ( SQLException e ){
       System.out.println("in SQLException");
   return null;
}

Answer 1

In the contextInitialized you have not created an instance of DBConnection! you've just called some static methods of this latter class.
If you want to create a DBConnection instance in the contextInitialized method, so use singleton pattern like the following:
import java.sql.*;
public class DBConnection {
     private static Connection connection = null;
     private static DBConnection instance = null;
     private static String driver;
     private static String dbURL;
     private static String username;
     private static String password;
     private DBConnection() {
     public static String getDbURL() {
          return dbURL;
     public static void setDbURL(String dbURL) {
          DBConnection.dbURL = dbURL;
     public static String getDriver() {
          return driver;
     public static void setDriver(String driver) {
          DBConnection.driver = driver;
     public static String getPassword() {
          return password;
     public static void setPassword(String password) {
          DBConnection.password = password;
     public static String getUsername() {
          return username;
     public static void setUsername(String username) {
          DBConnection.username = username;
     public synchronized final static DBConnection getInstance() {
          return (instance == null) ? new DBConnection() : instance;
     public static Connection getConnection() throws Exception{// you can remove throws Exception
          if(connection == null){
               throw new Exception("The DB connection may have not been initialized");//you can return null instead
          createConnection();
          return connection;
     private static void createConnection() {
          try {
               Class.forName(driver); // load the JDBC "driver" class
               connection = DriverManager.getConnection(dbURL, username, password); // get connection
          } catch (ClassNotFoundException e) {
               System.out.println("in ClassNotFoundException");
          } catch (SQLException e) {
               System.out.println("in SQLException");
}You should then do this :
DBConnection instance = DBConnection.getInstance(driver, dbURL, username,
password);
instance .setUsername (username);
     instance .setPassword (password);
     instance .setDbURL (dbURL);
     instance .setDriver (driver);instead of : DBConnection.setUsername (username);
     DBConnection.setPassword (password);
     DBConnection.setDbURL (dbURL);
     DBConnection.setDriver (driver);hth
Message was edited by:
java_2006