Is rollback needed if java.sql.Connection#commit() throws exception?

Question

According to JAVA documentation, Connection#commit() can throw SQLException. My question is whether or not a rollback should still be issued in this scenario.

For example:

Connection con = null;
try {
    // assume this method returns an opened connection with setAutoCommit(false)
    con = createConnection(); 

    // do DB stuff

    con.commit();
} catch (SQLException e) {
    if (con != null) {
        // what if con.commit() failed, is this still necessary,
        // will it hurt anything?
        con.rollback();
    }
} finally {
    if (con != null) {
        con.close();
    }
}

I actually wrapped the con.rollback() call into another method which ignores any exceptions thrown by it, so I think I'm ok here. I just wondered if this was the best way of handling things.

Answer 1

Rollback is important even if commit failed, according to the Java 1.6 JDBC docs:

It is strongly recommended that an application explicitly commits or rolls back an active transaction prior to calling the close method. If the close method is called and there is an active transaction, the results are implementation-defined.

This means that if you do not explicitly invoke rollback, some JDBC implementation might invoke commit before closing the connection.

Another good reason to rollback is as Xepoch suggested and when using a connection pool it is even more important. When getting a connection from a connection pool, most implementations will execute connection.setAutoCommit(defaultAutoCommit) before giving you the connection and according to the JavaDocs:

If this method is called during a transaction and the auto-commit mode is changed, the transaction is committed

If the connection.rollback() throws an exception - then it is a tricky one...