I'm trying to change main method of my Test class using BCEL. I simply want to add System.out.println("This is added by BCEL at runtime")
to the beginning of the main(). Although I don't receive exception and InstructionList shows my commands, my string is not printed and javap -c shows unmodified version.
Here is my code:
public static void main(String[] args) {
try {
JavaClass jc = Repository.lookupClass("Test");
System.out.println("Found class" + jc.getClassName());
ClassGen cg = new ClassGen(jc);
ConstantPoolGen cpg = cg.getConstantPool();
for (org.apache.bcel.classfile.Method m : jc.getMethods()) {
if (m.getName().equals("main")) {
MethodGen mg = new MethodGen(m, cg.getClassName(), cpg);
InstructionList list = mg.getInstructionList();
int stringIndex = cpg.addString("This is added by BCEL at runtime");
System.out.println("String index = " + stringIndex);
int soutIndex = cpg.lookupFieldref("java.lang.System", "out", "Ljava/io/PrintStream;");
System.out.println("Sout index = " + soutIndex);
int printlnIndex = cpg.lookupMethodref("java.io.PrintStream", "println", "(Ljava/lang/String;)V");
System.out.println("Println index = " + printlnIndex);
InstructionList patch = new InstructionList();
patch.append(new GETSTATIC(soutIndex));
patch.append(new LDC(stringIndex));
patch.append(new INVOKEVIRTUAL(printlnIndex));
list.insert(list.getInstructionHandles()[0], patch);
mg.setMaxStack();
File f = new File(Repository.lookupClassFile(cg.getClassName()).getPath());
cg.getJavaClass().dump(f.getPath());
System.out.println(f.getPath());
for (InstructionHandle ih : list.getInstructionHandles()) {
System.out.println(ih.getInstruction().toString());
}
}
}
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
