A single PSQL JDBC connection can easily serve multiple threads. However, while the Connection may be thread-safe, the objects created by the Connection are not. For example, a user can create four threads. Each of these threads could be given their own Statement object (all created by the same Connection object). All four threads could be sending or requesting data over the same connection at the same time. This works because all four Statement objects have a reference to the same Connection object and their reading and writing is synchronized on this object. However, thread #1 cannot access the Statement object in thread #2 without this access being synchronized. The above is true for all other objects in the JDBC API.