How to remove a method using Javassist?

Question

I am trying to delete a method from a class file using Javassist.

Target class:"RemoveMethod".

Target method:"DoubleCheck".

My codes:

package javassist;     
        import java.io.IOException;
        import java.lang.reflect.Method;
        import javassist.*;

public class cRepair {
    public static void main(String[] args) throws NotFoundException, IOException, CannotCompileException{
    ClassPool pool = ClassPool.getDefault();  
    CtClass ctClass = pool.get("javassist.RemoveMethod");  
    CtMethod ctm = ctClass.getDeclaredMethod("DoubleCheck");  
    ctClass.removeMethod(ctm);
    ctClass.writeFile("C:/Users/workspace/Javaproject1/src/javassis"); 
 }
}

Then,run the code using the file "javassist.jar":

javac -cp javassist.jar cRepair.java

Then check the target class:

javap -verbose RemoveMethod.class

The method "DoubleCheck" is still there!

This looks really odd. Why could this happen and how to fix it?

Answer 1

Your code reads the bytecode of your class into memory and removes the method. But it does not write the modified bytecode back to a .class file. You can call CtClass#writeFile() to do that.