Question

I am using MYSQL database and basic JDBC connection pool for connect to the database. application is deployed in tomcat server. After few operations, database connection getting null.

could any one please let me know the reason for that ?

Answer 1

This can happen for a few different reasons:

1. Not calling close() on your Connection resources when you’re done with them. This can cause your connection pool to be exhausted after all the Connections are handed out and not closed.
2. Calling close() on your Connection resources more than once. Closing a Connection returns it to the pool so another thread can grab it. If you call close() a second time, you’ve now closed it for the other thread.
3. Your code is actually setting your Connection instance to null somewhere.
4. You’re leaving a Connection resource open and idle for too long and it’s timing out on you. If your code has some long running operation between queries, consider closing the Connection and getting a new one between queries.
5. The database server closed your connection for some reason and your connection pool doesn’t know about it. To mitigate this, you can configure your connection pool to test on borrow. This would basically issue a test query on the connection to make sure it’s alive before handing it over to you app. Note: there is some overhead there.