connection.close() does not close the connection at server side

I am doing some data validations on Oracle DB. There are 10 different types of validations I have to do. Each set of validation contains hundreds of test cases. To save time, I am running the validations in parallel on 10 different threads. Each thread opens a database connection, execute the test cases and then close the connection - and do the same for the next test case. The problem is that I can have maximum of 8 concurrent oracle sessions. It is currently not possible to increase the number of sessions. To handle this scenario, I am using Semaphore to limit the number of concurrent oracle sessions to 8

public class DatabaseConnection{
 Semaphore counter = new Semaphore(8);
 public Connection createConnection(){
   ...
   ...
   counter.acquire();
   Connection connection = DriverManager.getConnection(....
   ...
}

public closeConnection(Connection con){
  ...
  con.close();
  counter.release();
}
}

Eventhough I am closing the connections properly after executing each test, I am getting maximum number of sessions exceeded exception. I suspects eventhough I close the connections, it is not properly closed at server side. What is the solution for this?

> I am running the validations in parallel on 10 different threads.

I wonder how are you running the parallel tests? Is it possible that you will end up with 10 instances of the DatabaseConnection class? If yes then you will also get 10 semaphores counting 8 times each. In this case the maximum number of connections will be 80... You can avoid it declaring the semaphore as static.

static Semaphore counter = new Semaphore(8);