Java bytecode manipulation framework

 It can be used to dynamically generate stub classes or other proxy classes,
 directly in binary form, or to dynamically modify classes at load time, i.e.,
 just before they are loaded into the Java Virtual Machine.
 .
 ASM offers similar functionalities as BCEL or SERP, but is much smaller
 (25KB instead of 350KB for BCEL and 150KB for SERP) and faster
 than these tools (the overhead of a load time class transformation is on
 the order of 60% with ASM, 700% or more with BCEL, and 1100% or more with
 SERP). ASM was designed to be used in a dynamic and static way and was
 therefore designed and implemented to be as small and as fast as possible.