ObjectWeb ASM

ObjectWeb
Developer(s)	OW2 Consortium
Stable release	4.1 / October 14, 2012 (2012-10-14)
Written in	Java
Operating system	Cross-platform
Type	bytecode Engineering Library
License	BSD License
Website	http://asm.objectweb.org/

The ASM library is a project of the ObjectWeb consortium. It provides a simple API for decomposing, modifying, and recomposing binary Java classes (i.e. bytecode). The project was originally conceived and developed by Eric Bruneton. ASM is Java-centric at present, and does not currently have a backend that exposes other bytecode implementations (such as .NET bytecode, Python bytecode, etc.).

Uses

ASM provides a simple library that exposes the internal aggregate components of a given Java class through its visitor oriented API. ASM also provides, on top of this visitor API, a tree API that represents classes as object constructs. Both APIs can be used for modifying the binary bytecode, as well as generating new bytecode (via injection of new code into the existing code, or through generation of new classes altogether.) The ASM library has been used in several diverse applications, such as:

Performance and Profiling

Instrumentation calls that capture performance metrics can be injected into Java class binaries to examine memory/coverage data. (For example, injecting instrumentation at entry/exit points.)

Implementation of New Language Semantics

For example, Groovy uses ASM to generate its bytecode. Also, Aspect-Oriented additions to the Java language have been implemented by using ASM to decompose class structures for point-cut identification, and then again when reconstituting the class by injecting aspect-related code back into the binary. (See: AspectWerkz)