Since "J2EE" has changed a lot over the years, I recommend first that you determine which J2EE version the application was built with [1], which application ser

Since "J2EE" has changed a lot over the years, I recommend first that you determine which J2EE version the application was built with [1], which application server it runs on, which middleware it uses and which frameworks it uses (such as Spring). Then look for a book about the relevant J2EE version and frameworks. [1] http://en.wikipedia.org/wiki/Java_EE_version_history http://en.wikipedia.org/wiki/Java_EE_version_history