Poor coding on my part?

Question

I used JMeter to test a servlet/jsp combination on Tomcat 3.3a (running on Mandrake 8.1) last night, and I'm questioning the results.
I set 75 threads in JMeter to call a servlet with the following code in the doGet method.
TestBean tb = new TestBean();
Class.forName("org.postgresql.Driver");
Connection con = DriverManager.getConnection(connectString, user, password);
ResultSet rs = con.createStatement().executeQuery("Select count(*) from directory");
while(rs.next()) {
tb.setCount(rs.getString(1));
con.close();
request.setAttribute("tb", tb);
RequestDispatcher rd = this.getServletContext().getRequestDispatcher("/test.jsp");
rd.forward(request, response);
I used a Gaussian timer that called the servlet every 300 ms, with a variance of 100 ms.
Started it running last night before bed, and when I got up this morning to check it, Tomcat was out of memory.
As I've been thinking about it, I wonder if I didn't cause that with poor programming techniques. I closed the connection, but does the con.createStatement() instantiate a Statement object that remains in memory?
Does the fact that I don't close the ResultSet cause a huge pile of ResultSet objects to remain in memory as well?
If the answer to both of these questions is no, do you see anything else in my code that might cause a memory leak?
Thanks for your help.

Answer 1

In addition to the things mentioned above (esp moving Class.forName(...) to init() ), I recommend you have a look at your error handling.
The defensive way of programming JDBC is to always use the "try {} finally {}" construct after creating a JDBC resource. In your case, the code would look liike this:
TestBean tb = new TestBean();
// Class.forName("org.postgresql.Driver"); moved to init
try {
  Connection con = DriverManager.getConnection(connectString, user, password);
  try {
    Statement stmt = con.createStatement();
    try {
      ResultSet rs = stmt.executeQuery("Select count(*) from directory");
      while(rs.next()) {
        tb.setCount(rs.getString(1));
    finally {
      stmt.close();
  finally {
    con.close();
  request.setAttribute("tb", tb);
  RequestDispatcher rd = this.getServletContext().getRequestDispatcher("/test.jsp");
  rd.forward(request, response);
catch (SQLException ex) {
  throw new ServletException(ex);
}This makes sure doGet always tries to close both the connection and the statement.
Creating a new connection each time you want to access the database is bound to kill your performance, by the way. You should look into some sort of connection pooling, or maybe creating the connection in init() and always synchronizing its use.
And a last point: you should check whether the JDBC driver you're using is leaking memory. Create a standalone program that basically does the same as your doGet method, then have a look at how much memory is consumed by running java with gc logging enabled.