Java programming dynamics, Part 7: Bytecode engineering with BCEL
Apache BCEL lets you get to the details of JVM assembler language for classworking
The Apache Byte Code Engineering Library (BCEL) lets you dig into the bytecode of Java classes. You
Tutorial Details:
In the last three articles of this series, I\'ve shown you how to use the Javassist framework for classworking. This time I\'m going to cover a very different approach to bytecode manipulation, using the Apache Byte Code Engineering Library (BCEL). BCEL operates at the level of actual JVM instructions, unlike the source code interface supported by Javassist. The low-level approach makes BCEL very good for when you really want to control every step of the program execution, but it also makes working with BCEL a lot more complex than using Javassist for cases where both will work.
I\'m going to start out by covering the basic BCEL architecture, then devote most of this article to rebuilding my first Javassist classworking example with BCEL. I\'ll finish up with a quick look at some of the tools included in the BCEL package and some of the applications developers have built on top of BCEL.
BCEL class access
BCEL gives you all the same basic capabilities as Javassist to inspect, edit, and create Java binary classes. The obvious difference with BCEL is that everything is designed to work at the level of JVM assembler language, rather than the source code interface provided by Javassist. There are some deeper differences under the covers, including the use of two separate hierarchies of components within BCEL -- one for inspecting existing code and the other for creating new code. I\'m going to assume you\'re familiar with Javassist from the previous articles in this series (see the sidebar Don\'t miss the rest of this series). I\'ll therefore concentrate on the differences that are likely to confuse you when you start working with BCEL.
As with Javassist, the class inspection aspect of BCEL basically duplicates what\'s available directly in the Java platform through the Reflection API. This duplication is necessary in a classworking toolkit because you generally don\'t want to load the classes you\'re working with until after they\'ve been modified.
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Java programming dynamics, Part 7: Bytecode engineering with BCEL
Java programming dynamics, Part 7: Bytecode engineering with BCEL
Apache BCEL lets you get to the details of JVM assembler language for classworking
The Apache Byte Code Engineering Library (BCEL) lets you dig into the bytecode of Java classes. You
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