bytecode

I'm having difficulty understanding the documentation for Byte Buddy . To help me learn the API I would like to generate the byte code equivalent of this Java: public final class GeneratedByByteBuddy { private final int a; public GeneratedByByteBuddy(final int a) { this.a = a; } } I've had difficulty working out the right way to use Instrumentation to create the field assignment. You are creating a class with customized byte code. For this, you cannot use a built-in Instrumentation but you need to write your own instrumentation which creates the particular byte code for your constructor. This

I need to create a java agent that when is enabled it gets the path to a jar file as argument and then it replaces any loaded class the the one inside the jar file if their names are matched. For example, we have an application with a class called com.something.ClassTest. Now if the mentioned jar (is not in the class path) has a class exactly the same name as com.something.ClassTest, I want to replace it with the one in the jar. I have this class transformer but not sure if that's correct or not. I get IOException with message Class not found. @Override public byte[] transform(ClassLoader

Disassembling some Java 8 code I found out that some invokestatic calls on static methods in interface (particularly this was java.util.function.Function.identity() ) uses InterfaceMethodRef in const pool; this is what javap -s -c -v p show me: 15: invokestatic #66 // InterfaceMethod java/util/function/Function.identity:()Ljava/util/function/Function; According to JVM 8 spec this is not possible, and when I've used this instruction in classfile with version Java 7 ( major version=51 ), it has thrown VerifyError on this instruction. However, when I've changed the major version to 52 , it

Today I was exploring classes of huge applications (like jboss server with apps) with javaagent and instrumentation on my openjdk 7. I called retransform on all classes every 10 seconds, so their bytecode got in my ClassFileTransformer implementation. My implementation simply keeps track of how bytecode of classes changes over time. First of all, I was surprised, that order of fields and methods, method access modifiers, contents of constant pool and other such things vary from one check to the other. But, still, it is documented . What is not documented - that some items may be created in

By "Magic" I mean the methods which have semantics which are not expressed in pure Java. I know all native methods are magic, in that their implementation is provided by the underlying runtime and not by Java bytecodes. Is the reverse true? Are all magic methods native , or are there some magic methods apparently implemented in pure Java, but with some extra help from some JVM-special-casing? The use case is that I want to modify the semantics of Java by instrumenting its bytecodes. All these magic methods are special cases which I will have to handle some way or another. The native ones are

There are some constructs that don't have equivalents in java. Examples would be named parameters instance private members Where/How does Scala store the information necessary for this stuff (some kind of flag in the first case, the parameter names in the second case? If I get it right this has to get stored in the byte code, since it works even if I just have a compiled library without the source code!? Travis Brown This information is captured in an annotation named ScalaSig in the class file (see this answer for an example). You can view the (not very human-friendly) annotation with javap