方法：删除

预期目标

假如有一个HelloWorld类，代码如下：

public class HelloWorld {
    public int add(int a, int b) {
        return a + b;
    }

    public int sub(int a, int b) {
        return a - b;
    }
}

我们想实现的预期目标：将HelloWorld类的add方法删除。

编码实现

import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.MethodVisitor;

public class ClassRemoveMethodVisitor extends ClassVisitor {
    private final String methodName;
    private final String methodDesc;

    public ClassRemoveMethodVisitor(int api, ClassVisitor cv, String methodName, String methodDesc) {
        super(api, cv);
        this.methodName = methodName;
        this.methodDesc = methodDesc;
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
        if (name.equals(methodName) && descriptor.equals(methodDesc)) {
            return null;
        }
        return super.visitMethod(access, name, descriptor, signature, exceptions);
    }
}

进行转换

import lsieun.utils.FileUtils;
import org.objectweb.asm.*;

public class HelloWorldTransformCore {
    public static void main(String[] args) {
        String relative_path = "sample/HelloWorld.class";
        String filepath = FileUtils.getFilePath(relative_path);
        byte[] bytes1 = FileUtils.readBytes(filepath);

        //（1）构建ClassReader
        ClassReader cr = new ClassReader(bytes1);

        //（2）构建ClassWriter
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);

        //（3）串连ClassVisitor
        int api = Opcodes.ASM9;
        ClassVisitor cv = new ClassRemoveMethodVisitor(api, cw, "add", "(II)I");

        //（4）结合ClassReader和ClassVisitor
        int parsingOptions = ClassReader.SKIP_DEBUG | ClassReader.SKIP_FRAMES;
        cr.accept(cv, parsingOptions);

        //（5）生成byte[]
        byte[] bytes2 = cw.toByteArray();

        FileUtils.writeBytes(filepath, bytes2);
    }
}

总结