Janino 

Janino is a compiler that reads a Java expression, block, or source file, and generates Java bytecode that is loaded and executed directly. It is not intended to be a development tool, but an embedded compiler for run-time compilation purposes.
java compiler embedded expression evaluation script scripting jvm virtual machine run-time compilation jsp

RetroGuard 

RetroGuard, a general purpose Java obfuscator, is designed to fit effortlessly into your regular build and testing process, providing peace of mind that your valuable Java bytecode is more secure against decompilation and reverse engineering.
retroguard java obfuscator java obfuscation java bytecode retrologic obfuscator obfuscation