1<?xml version="1.0"?> 2<!-- 3 * Licensed to the Apache Software Foundation (ASF) under one 4 * or more contributor license agreements. See the NOTICE file 5 * distributed with this work for additional information 6 * regarding copyright ownership. The ASF licenses this file 7 * to you under the Apache License, Version 2.0 (the 8 * "License"); you may not use this file except in compliance 9 * with the License. You may obtain a copy of the License at 10 * 11 * http://www.apache.org/licenses/LICENSE-2.0 12 * 13 * Unless required by applicable law or agreed to in writing, 14 * software distributed under the License is distributed on an 15 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 16 * KIND, either express or implied. See the License for the 17 * specific language governing permissions and limitations 18 * under the License. 19--> 20<document> 21 <properties> 22 <title>Introduction</title> 23 </properties> 24 25 <body> 26 27 <section name="Introduction"> 28 <p> 29 The <a href="http://java.sun.com/">Java</a> language has become 30 very popular and many research projects deal with further 31 improvements of the language or its run-time behavior. The 32 possibility to extend a language with new concepts is surely a 33 desirable feature, but the implementation issues should be hidden 34 from the user. Fortunately, the concepts of the Java Virtual 35 Machine permit the user-transparent implementation of such 36 extensions with relatively little effort. 37 </p> 38 39 <p> 40 Because the target language of Java is an interpreted language 41 with a small and easy-to-understand set of instructions (the 42 <em>byte code</em>), developers can implement and test their 43 concepts in a very elegant way. One can write a plug-in 44 replacement for the system's <em>class loader</em> which is 45 responsible for dynamically loading class files at run-time and 46 passing the byte code to the Virtual Machine (see <a 47 href="jvm.html">section 2</a>). 48 Class loaders may thus be used to intercept the loading process 49 and transform classes before they get actually executed by the 50 JVM. While the original class files always remain unaltered, the 51 behavior of the class loader may be reconfigured for every 52 execution or instrumented dynamically. 53 </p> 54 55 <p> 56 The <font face="helvetica,arial">BCEL</font> API (Byte Code 57 Engineering Library), formerly known as JavaClass, is a toolkit 58 for the static analysis and dynamic creation or transformation of 59 Java class files. It enables developers to implement the desired 60 features on a high level of abstraction without handling all the 61 internal details of the Java class file format and thus 62 re-inventing the wheel every time. <font face="helvetica,arial">BCEL 63 </font> is written entirely in Java and freely available under the 64 terms of the <a href="license.html">Apache Software License</a>. 65 </p> 66 67 <p> 68 This manual is structured as follows: We give a brief description 69 of the Java Virtual Machine and the class file format in <a 70 href="jvm.html">section 2</a>. <a href="bcel-api.html">Section 3</a> 71 introduces the <font face="helvetica,arial">BCEL</font> API. 72 <a href="application-areas.html">Section 4</a> describes some typical 73 application areas and example projects. The appendix contains code examples 74 that are to long to be presented in the main part of this paper. All examples 75 are included in the down-loadable distribution. 76 </p> 77 </section> 78 79 </body> 80 81</document>