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 21 <document> 22 23 <properties> 24 <title>BCEL FAQ</title> 25 </properties> 26 27 <body> 28 29 <section name="FAQ"> 30 <p> 31 <b>Q: </b>How can I ... with BCEL? 32 <br/> 33 <b>A: </b>Take a look at 34 <tt>org.apache.bcel.util.BCELifier</tt>, it takes a given class 35 and converts it to a BCEL program (in Java, of course). It will 36 show you how certain code is generated using BCEL. 37 </p> 38 39 <p> 40 <b>Q: </b> Is the BCEL thread-safe? 41 <br/> 42 <b>A: </b>BCEL was (deliberately) not designed for thread 43 safety. See <a href="http://java.sun.com/docs/books/cp/"> 44 "Concurrent Programming in Java"</a>, by Doug Lea, 45 for an excellent reference on how to build thread-safe wrappers. 46 </p> 47 48 <p> 49 <b>Q: </b> Can I use BCEL in a commercial product? 50 <br/> 51 <b>A: </b> Yes, this is covered by the <a 52 href="http://www.apache.org/licenses/">Apache License</a>, if you add a note about the original 53 author and where to find the sources, i.e., 54 <a href="http://commons.apache.org/bcel/">http://commons.apache.org/bcel/</a> 55 </p> 56 57 <p> 58 <b>Q: </b> (Typically for users of Xalan (XSLTC)) I'm getting 59 <pre> 60 ClassGenException: Branch target offset too large for short 61 </pre> 62 when compiling large files. 63 <br/> 64 65 <b>A: </b> The answer lies in internal limitations of the JVM, 66 branch instruction like goto can not address offsets larger than 67 a short integer, i.e. offsets >= 32767.<br/> 68 The solution is to split the branch into in intermediate hops, 69 which the XSLTC obviously doesn't take care off. 70 (In fact you could replace gotos with the goto_w instruction, 71 but this wouldn't help in the other cases). 72 </p> 73 74 <p> 75 <b>Q:</b> Can I create or modify classes dynamically with BCEL? 76 <br/> 77 <b>A:</b> BCEL contains useful classes in the 78 <tt>util</tt> package, namely <tt>ClassLoader</tt> and 79 <tt>JavaWrapper</tt>. Take a look at the <tt> ProxyCreator</tt> example. 80 </p> 81 82 <p> 83 <b>Q:</b> I get a verification error, what can I do? 84 <br/> 85 <b>A:</b> Use the JustIce verifier that comes together with BCEL 86 to get more detailed information: 87 <pre> 88 java org.apache.bcel.verifier.Verifier <your class></pre> 89 </p> 90 91 </section> 92 <!-- 93 <p> 94 <b>Q: </b> 95 <br/> 96 <b>A: </b> 97 </p> 98 --> 99 </body> 100 </document> 101
