For codenbases... Objectweb ASM blew my mind. It's a library to read/write java class files. The core at that time would fit into 2 java files. It was a reade

For codenbases... Objectweb ASM blew my mind. It's a library to read/write java class files. The core at that time would fit into 2 java files. It was a reader and a writer built around a visitor pattern. At that time apache bcel was also big, a library to build in-memory class file representations which you would then manipulate. ASM allowed you to do many transformation without ever holding the whole file in memory. ASM also had an in-memory representation as an add-on. It was all nicely layered and the core was just a marvelous small piece of code, with incredible low memory consumption.