g

java

package github.huzpsb.nm.sample;

import github.huzpsb.nm.tools.Hacker;
import org.objectweb.asm.*;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;

public class Main {
    public static void main(String[] args) throws Exception {
        Instrumentation ins = Hacker.getInsn();
        final String tgt = "github/huzpsb/nm/sample/Add";
        ClassFileTransformer ret = new ClassFileTransformer() {
            public byte[] transform(ClassLoader loader,
                                    String className,
                                    Class<?> classBeingRedefined,
                                    ProtectionDomain protectionDomain,
                                    byte[] classfileBuffer)
                    throws IllegalClassFormatException {
                if (className.equals(tgt)) {
                    ClassReader cr = new ClassReader(classfileBuffer);
                    ClassWriter cw = new ClassWriter(cr, 0);
                    ClassVisitor cv = new ClassVisitor(Opcodes.ASM9, cw) {
                        @Override
                        public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
                            if (name.equals("add")) {
                                System.out.println("Found the target method");

                                return null;
                            }
                            return super.visitMethod(access, name, descriptor, signature, exceptions);
                        }

                        @Override
                        public void visitEnd() {
                            // Create the new onCustomPayload method
                            MethodVisitor mv = cv.visitMethod(Opcodes.ACC_PUBLIC | Opcodes.ACC_STATIC, "add", "(II)I", null, null);
                            mv.visitCode();
                            mv.visitVarInsn(Opcodes.ILOAD, 0);
                            mv.visitVarInsn(Opcodes.ILOAD, 1);
                            mv.visitInsn(Opcodes.IMUL);
                            mv.visitInsn(Opcodes.IRETURN);
                            mv.visitMaxs(2, 2);
                            mv.visitEnd();
                        }
                    };
                    cr.accept(cv, 0);
                    return cw.toByteArray();
                }
                return classfileBuffer;
            }
        };
        ins.addTransformer(ret, true);
        ins.retransformClasses(Add.class);
        System.out.println(Add.add(2, 3));
    }
}