There are a couple of things you should be aware of when obfuscating and shrinking software. The weakest part of an application considering name obfuscation and code shrinking is code that uses reflection to dynamically load classes, invoke methods etc. Therefore, you have to be especially careful when using the yguard task on applications that rely on reflection. The most important facts to keep in mind when using yGuard are described here briefly:

  • If you use the rename task, code in the form of MyApplication.class will break if MyApplication will be obfuscated by name and the obfuscation switch replaceClassNameStrings is set to false. The shrink task will currently recognize code in the form of MyApplication.class only if the java files were compiled using an arbitrary version of the standard javac compiler (although the shrinking engine might recognize the .class construct also if the classes were compiled using a compiler that generates similar bytecode).
  • Automatic introspection and reflection will break in most cases, when you decide to obfuscate the corresponding methods and fields. If you use the shrink task and your application uses reflection you should explicitly designate all entities loaded per reflection as code entrypoints using the keep element. If your application is broken after using the shrink task, consider using the createStubs attribute of the shrink task to find out which additional entities you need to include in the keep element.
  • Class.forName(className) will not work when using the rename task unless you use the obfuscated name string in your variable or the String is a local constant and replaceClassNameStrings is not set or set to true. If you use the shrink task, className should be contained in the list of entrypoints using the keep element.
  • The customized serialization mechanism will not work if you obfuscated or shrinked the writeObject and readObject methods as well as the serializationUID field.
  • Simple bean introspection will not work, if you decide to obfuscate your public accessor methods, since it makes use of reflection.
  • If you do not set the -Xmx property for the Java virtual machine, the yguard Ant task might fail due to a java.lang.OutOfMemoryError. To solve this problem, set the -Xmx option in the ANT_OPTS variable, e.g.:
bash> export ANT_OPTS="-Xmx512M"
cshell> setenv ANT_OPTS "-Xmx512M"