The Byte Code Engineering Library (BCEL) is a project sponsored by the Apache Foundation under their Jakarta

Jakarta Project

The Jakarta Project creates and maintains open source software for the Java platform. It operates as an umbrella project under the auspices of the Apache Software Foundation, and all of Jakarta products are released under the Apache License.-Subprojects:...

 charter to provide a simple API for decomposing, modifying, and recomposing binary Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

 classes (I.e. bytecode

Bytecode

Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...

). The project was originally conceived and developed by Markus Dahm prior to officially being donated to the Apache Jakarta foundation on 27 October 2001. BCEL is Java-centric at present, and does not currently have a backend that exposes other bytecode implementations (such as .NET

.NET Framework

The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...

 bytecode, Python

Python (programming language)

Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...

 bytecode, etc.).

Uses

BCEL provides a simple library that exposes the internal aggregate components of a given Java class through its API as object constructs (as opposed to the disassembly of the lower-level opcodes). These objects also expose operations 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 BCEL library has been used in several diverse applications, such as:

• Java Bytecode Decompiling, Obfuscation, and Refactoring
• 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, Aspect-Oriented additions to the Java language have been implemented by using BCEL 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: AspectJ

AspectJ

AspectJ is an aspect-oriented extension created at PARC for the Java programming language. It is available in Eclipse Foundation open-source projects, both stand-alone and integrated into Eclipse. AspectJ has become the widely-used de-facto standard for AOP by emphasizing simplicity and usability...

)

• Static code analysis
  Static code analysis
  Static program analysis is the analysis of computer software that is performed without actually executing programs built from that software In most cases the analysis is performed on some version of the source code and in the other cases some form of the object code...
  
  

FindBugs

FindBugs

FindBugs is an open source program created by Bill Pugh and David Hovemeyer which looks for bugs in Java code. It uses static analysis to identify hundreds of different potential types of errors in Java programs. FindBugs operates on Java bytecode, rather than source code. The software is...

uses BCEL to analyze Java bytecode for code idioms which indicate bugs.

External links

• Jakarta ByteCode Engineering Library - The BCEL Project Home Page.
• BCEL-Based Project Listing - A listing of projects that make use of the BCEL Library.
• Apache Jakarta Home - The Apache Jakarta Home Page.
• AspectJ - The AspectJ Project Home Page. (One of the high-visibility projects that makes use of BCEL.)