ConnectionPooling problem...

Question

Hello,
I am having a problem with my database driver. The thing is that the class is compiling correctly, but only when I execute the createPool() function from one of my JSP's, do I get the following 500 Servlet Exception (the ConnectionPool class follows the error):
java.lang.ClassNotFoundException: org.gjt.mm.mysql.Driver
     at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:297)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:286)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:253)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:313)
     at java.lang.Class.forName0(Native Method)
     at java.lang.Class.forName(Class.java:120)
     at ConnectionPool.createPool(ConnectionPool.java:165)
     at jsp.www__isbops__com._80_0._index__jsp._jspService(//inc1.jsp:14)
     at com.caucho.jsp.JavaPage.service(JavaPage.java:89)
     at com.caucho.jsp.JavaPage.subservice(JavaPage.java:83)
     at com.caucho.jsp.Page.service(Page.java:409)
     at com.caucho.server.http.Invocation.service(Invocation.java:266)
     at com.caucho.server.http.RunnerRequest.handleRequest(RunnerRequest.java:349)
     at com.caucho.server.http.RunnerRequest.handleConnection(RunnerRequest.java:265)
     at com.caucho.server.TcpConnection.run(TcpConnection.java:142)
     at java.lang.Thread.run(Thread.java:484)
ConnectionPool.java:
Here is the connection pool class, which compiles correctly, so I don't think it is a classpath problem. Though I do correctly point to the jar file that contains the driver, and I don't "import" the driver. I have no idea what's wrong:
import java.sql.*;
import java.util.*;
public class ConnectionPool
  private String jdbcConnection = "<hidden for the java forum>";
  private String dbUsername = "<hidden>";
  private String dbPassword = "<hidden>";
  private String testTable = "testConnectionPool";
  private int initialConnections = 10;
  private int incrementalConnections = 5;
  private int maxConnections = 50;
  private Vector connections = null;
   public ConnectionPool() {}
  public int getInitialConnections()
    return initialConnections;
  public void setInitialConnections(int initialConnections)
    this.initialConnections = initialConnections;
  public int getIncrementalConnections()
    return incrementalConnections;
  public void setIncrementalConnections(
    int incrementalConnections)
    this.incrementalConnections = incrementalConnections;
  public int getMaxConnections()
    return maxConnections;
  public void setMaxConnections(int maxConnections)
    this.maxConnections = maxConnections;
  public String getTestTable()
    return testTable;
  public void setTestTable(String testTable)
    this.testTable = testTable;
  public synchronized void createPool() throws Exception
    if (connections != null)
      return;
    Class.forName("org.gjt.mm.mysql.Driver").newInstance();
    connections = new Vector();
    createConnections(initialConnections);
  public boolean isPooled() throws Exception {
    if(connections == null) {
      return false;
    return true;
  private void createConnections(int numConnections) throws
    SQLException
    for (int x=0; x < numConnections; x++)
      if (maxConnections > 0 &&
        connections.size() >= maxConnections)
        break;
      //add a new PooledConnection object to connections vector
      connections.addElement(new PooledConnection(
        newConnection()));
      System.out.println("Database connection created...");
  private Connection newConnection() throws SQLException
    //create a new database connection
    Connection conn = DriverManager.getConnection(jdbcConnection,
      dbUsername, dbPassword);
    if (connections.size() == 0)
      DatabaseMetaData metaData = conn.getMetaData();
      int driverMaxConnections = metaData.getMaxConnections();
      if (driverMaxConnections > 0 &&
        maxConnections > driverMaxConnections)
        maxConnections = driverMaxConnections;
    return conn;
  public synchronized Connection getConnection() throws
    SQLException
    if (connections == null)
      return null;
    Connection conn = getFreeConnection();
    while (conn == null)
      wait(250);
      conn = getFreeConnection();
    return conn;
  private Connection getFreeConnection() throws SQLException
    Connection conn = findFreeConnection();
    if (conn == null)
      createConnections(incrementalConnections);
      conn = findFreeConnection();
      if (conn == null)
        return null;
    return conn;
  private Connection findFreeConnection() throws SQLException
    Connection conn = null;
    PooledConnection pConn = null;
    Enumeration enum = connections.elements();
    while (enum.hasMoreElements())
      pConn = (PooledConnection)enum.nextElement();
      if (!pConn.isBusy())
        conn = pConn.getConnection();
        pConn.setBusy(true); //set connection to busy
        if (!testConnection(conn))
          conn = newConnection();
          pConn.setConnection(conn);
        break;
    return conn;
  private boolean testConnection(Connection conn)
    try
      if (testTable.equals(""))
        conn.setAutoCommit(true);
      else
        Statement stmt = conn.createStatement();
        stmt.execute("select count(*) from " + testTable);
    catch (SQLException e)
      //connection is no longer valid, attempt to close it
      closeConnection(conn);
      return false;
    return true;
  public void returnConnection(Connection conn)
    if (connections == null)
      return;
    PooledConnection pConn = null;
    Enumeration enum = connections.elements();
    while (enum.hasMoreElements())
      pConn = (PooledConnection)enum.nextElement();
      if (conn == pConn.getConnection())
        pConn.setBusy(false);
        break;
  public synchronized void refreshConnections() throws
    SQLException
    if (connections == null)
      return;
    PooledConnection pConn = null;
    Enumeration enum = connections.elements();
    while (enum.hasMoreElements())
      pConn = (PooledConnection)enum.nextElement();
      if (!pConn.isBusy())
        wait(10000); //wait 5 seconds
      closeConnection(pConn.getConnection());
      pConn.setConnection(newConnection());
      pConn.setBusy(false);
  public synchronized void closeConnections() throws SQLException
    if (connections == null)
      return;
    PooledConnection pConn = null;
    Enumeration enum = connections.elements();
    while (enum.hasMoreElements())
      pConn = (PooledConnection)enum.nextElement();
      if (!pConn.isBusy())
        wait(5000);
      closeConnection(pConn.getConnection());
      connections.removeElement(pConn);
    connections = null;
  private void closeConnection(Connection conn)
    try
      conn.close();
    catch (SQLException e)
  private void wait(int mSeconds)
    try
      Thread.sleep(mSeconds);
    catch (InterruptedException e)
  class PooledConnection
    Connection connection = null;
    boolean busy = false;
    public PooledConnection(Connection connection)
      this.connection = connection;
    public Connection getConnection()
      return connection;
    public void setConnection(Connection connection)
      this.connection = connection;
    public boolean isBusy()
      return busy;
    public void setBusy(boolean busy)
      this.busy = busy;
}

Answer 1

Hi,
The problem lies in the classpath. You should set the classpath of the webserver so as include the the jar file of the driver class which you are using.
If you still have any doubt, you can unzip all the classes that are present in the jar file to the directory where you place servlet class files.
Bye.