ResultSet not closed when connection closed?

Question

I've been doing code review (mostly using tools like FindBugs) of one of our pet projects and FindBugs marked following code as erroneous (pseudocode):

Connection conn = dataSource.getConnection();  try{     PreparedStatement stmt = conn.prepareStatement();     //initialize the statement     stmt.execute();     ResultSet rs =  stmt.getResultSet();     //get data }finally{     conn.close(); } 

The error was that this code might not release resources. I figured out that the ResultSet and Statement were not closed, so I closed them in finally:

finally{     try{         rs.close()     }catch(SqlException se){         //log it     }     try{         stmt.close();     }catch(SqlException se){         //log it     }     conn.close(); } 

But I encountered the above pattern in many projects (from quite a few companies), and no one was closing ResultSets or Statements.

Did you have troubles with ResultSets and Statements not being closed when the Connection is closed?

I found only this and it refers to Oracle having problems with closing ResultSets when closing Connections (we use Oracle db, hence my corrections). java.sql.api says nothing in Connection.close() javadoc.

Answer 1

One problem with ONLY closing the connection and not the result set, is that if your connection management code is using connection pooling, the connection.close() would just put the connection back in the pool. Additionally, some database have a cursor resource on the server that will not be freed properly unless it is explicitly closed.

Answer 2

I've had problems with unclosed ResultSets in Oracle, even though the connection was closed. The error I got was

"ORA-01000: maximum open cursors exceeded" 

So: Always close your ResultSet!