Hi all,
I fixed my problem.
This is my code transforming an existing constructor :
InstructionList originalIl = mg.getInstructionList();
InstructionHandle instructionHandle[] = originalIl.getInstructionHandles();
InstructionList newIl = new InstructionList();
newIl.append(factory.createInvoke("MySingleton", "getInstance", new
ObjectType("MySingleton"), Type.NO_ARGS, Constants.INVOKESTATIC));
newIl.append(InstructionFactory.createLoad(Type.OBJECT, 0));
newIl.append(factory.createInvoke("java.lang.Object", "getClass", new
ObjectType("java.lang.Class"), Type.NO_ARGS, Constants.INVOKEVIRTUAL));
newIl.append(factory.createInvoke("java.lang.Class", "getName", Type.STRING,
Type.NO_ARGS, Constants.INVOKEVIRTUAL));
newIl.append(InstructionConstants.ACONST_NULL);
newIl.append(factory.createInvoke("MySingleton", "myMethod", Type.VOID, new Type[] {
Type.STRING, new ObjectType("MyObject") }, Constants.INVOKEVIRTUAL));
// First let the super or other constructor be called!!!!!
for (int i = 1; i < instructionHandle.length; i++){
if (instructionHandle[i].getInstruction() instanceof INVOKESPECIAL){
originalIl.append(instructionHandle[i], newIl);
break;
}
}
The important part is the for loop. Looping through the original instruction list
until all constructors are called. Afterwards the instructions of the newIL variable
containing the new code are appended.
This is because the JVM spec states all constructor call's should be done before other
statements are executed in a constructor.
I hope my solution can help others. If you know a better solution please let us know.
Kind regards,
-----Oorspronkelijk bericht-----
Van: Johan Kumps [mailto:[EMAIL PROTECTED]
Verzonden: donderdag 15 juli 2004 13:26
Aan: [EMAIL PROTECTED]
Onderwerp: JavaClassFileOutputException: Stack underflow
Hi all,
I'm trying to insert some code in the constructor of certain classes. The code should
be getting the current singleton instance of a class 'MySingleton' and call a method
'myMethod' on this instance. My code is as follows :
InstructionList il = mg.getInstructionList();
il.insert(factory.createInvoke("MySingleTon", "getInstance", new
ObjectType("MySingleton"), Type.NO_ARGS, Constants.INVOKESTATIC));
il.insert(InstructionFactory.createLoad(Type.OBJECT, 0));
il.insert(factory.createInvoke("java.lang.Object", "getClass", new
ObjectType("java.lang.Class"), Type.NO_ARGS, Constants.INVOKEVIRTUAL));
il.insert(factory.createInvoke("java.lang.Class", "getName", Type.STRING,
Type.NO_ARGS, Constants.INVOKEVIRTUAL));
il.insert(InstructionConstants.ACONST_NULL);
il.insert(factory.createInvoke("MySingleton", "myMethod", Type.VOID, new Type[] {
Type.STRING, new ObjectType("MyObject") }, Constants.INVOKEVIRTUAL));
mg.setInstructionList(il);
mg.setMaxStack();
When I decompile the patched class the method to which I inserted the code has
dissapeared and the following line is added in place :
// JavaClassFileOutputException: Stack underflow
Does anybody has an idea of what I'm doing wrong? Can you provide me a code sample
doing something like I want to achieve?
Kind regards,
Johan,
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