Ensure that everything is closed?

Question

Hello,
I am using Sun Java Application Server 8 and Oracle 9i. I know that if you don't close all of your ResultSets, Statements and Connections, you'll get a error like "Error in allocating a connection. Cause: In-use connections equal max-pool-size and expired max-wait-time. Cannot allocate more connections.". When that happens you are pretty much hosed.
You can't just do a blanket try - catch, because depending upon where the error occurs, different objects are created, so you don't know which ones to close.
I started using a double try catch, like this
try {
Context initCtx = new InitialContext();
DataSource ds = (DataSource)initCtx.lookup("java:comp/env/jdbc/newsAdmin");
Connection con = ds.getConnection();
Statement stmt = con.createStatement();
try {
// blah blah blah
ResultSet rss = stmt.executeQuery("select * from my table");
// blah blah blah
rss.close();
} catch (Exception e) {
stmt.close();
con.close();
throw e;
stmt.close();
con.close();
} catch (Exception e) {
But there are still situations where something does not get closed. What is the plain vanilla way to ensure that everything gets closed? Also, is there a way to have the Servlet close everything on redirect? What about an application server setting? This seems pretty damgerious. One developer having a bad day could put code out there that locks up the applicaion server.
Thanks
Mike

Answer 1

public void foo()
   throws SQLException {
   Connection conn = null; 
   PreparedStatement stmt = null;
   ResultSet results = null;
   try {
         // create connection, statement and result set normally
    finally {
         closeResources(conn, stmt, results);
private void closeResources(final Connection conn, final Statement stmt, final ResultSet results) {
   if (results != null) {
       try {
           results.close();
       catch (SQLException ignroe) {
            ignore.printStackTrace();
   if (stmt != null) {
       try {
           stmt.close();
       catch (SQLException ignroe) {
            ignore.printStackTrace();
   if (conn != null) {
       try {
           conn.close();
       catch (SQLException ignroe) {
            ignore.printStackTrace();
}If you have more than one database operation that needs closing (which is likely the case), consider moving closeResources() to another helper object as a static method.
- Saish