Even though debugging can be tough, there are a number of techniques you can use to help you knock out the pests. Logging is a simple task that often produces the information you need without too much complexity. With Log4J or the Java 1.4 Logging APIs, you can produce software that gives you the right amount of information for different events without too much effort. For situations that require a closer look, debuggers are useful. Although they're more difficult to set up, particularly when working in distributed environments, they provide a perspective on the application that is difficult to get anywhere else.
Finally, well-designed applications will use error pages to handle unexpected exceptions in your JSPs or to inform users in a friendly way about content or server errors.