People often confuse performance and scalability testing, but they are actually quite different activities. Performance testing involves ensuring that your application responds to requests within an acceptable timeframe. Of course, defining what "acceptable" is is a fine art, and perceived performance (what the user actually sees) is often more important than real performance.

The classic difference between integration and unit testing is that unit tests run in isolation, or near-isolation. Using an in-memory database for DAO unit tests. Using mocked-out components for the other layers. Integration tests, on the other hand, test the whole stack. If you're using Spring, you inject the whole Spring context and try to flush out any configuration issues, or integration issues between the various layers.