Unfortunately, this depends on the capabilities of the driver. A JDBC Compliant driver is required to be thread safe, but some poorly written drivers do so by forcing Statements to run serially, so you can appear to be hung and results are not as expected. And, of course, some drivers are just poorly written, period.

you have to obtain a connection in the service method from the pool and not outside of the service method. a connection cannot have multiple statements open on it. this code above is not thread-safe. when client1 connects to the servlet and statement is created on the connection, if client2 connects before client1 finishes the execution (before connection is freed) SQLException will be thrown. so inside the service() method, get a connection from the pool, create a statement, execute a statement, close the statement, close the connection (return it to the pool). that would be a thread-safe way of doing it.