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<dependency>

    <groupId>org.ow2.asm</groupId>

    <artifactId>asm</artifactId>

    <version>9.4</version>

</dependency>

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package com.xu.test;

/**

 * @author Administrator

 */

public class Main {

    public void print() {

        System.out.println("ASM");

    }

}

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package com.xu.test;

import org.apache.commons.lang3.StringUtils;

import org.objectweb.asm.ClassVisitor;

import org.objectweb.asm.MethodVisitor;

import org.objectweb.asm.Opcodes;

/**

 * ASM 字节码增强技术

 *

 * @author Administrator

 */

public class CustomerClassVisitor extends ClassVisitor implements Opcodes {

    public CustomerClassVisitor(ClassVisitor api) {

        super(ASM9, api);

    }

    @Override

    public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {

        cv.visit(version, access, name, signature, superName, interfaces);

    }

    @Override

    public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {

        MethodVisitor mv = cv.visitMethod(access, name, descriptor, signature, exceptions);

        if (StringUtils.equals("print", name) && mv != null) {

            mv = new CustomerMethodVisitor(mv);

        }

        return mv;

    }

    class CustomerMethodVisitor extends MethodVisitor implements Opcodes {

        public CustomerMethodVisitor(MethodVisitor api) {

            super(ASM9, api);

        }

        @Override

        public void visitCode() {

            super.visitCode();

            mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");

            mv.visitLdcInsn("start");

            mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

        }

        @Override

        public void visitInsn(int opcode) {

            if ((opcode >= Opcodes.IRETURN && opcode <= Opcodes.RETURN) || opcode == Opcodes.ATHROW) {

                mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");

                mv.visitLdcInsn("end");

                mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

            }

            mv.visitInsn(opcode);

        }

    }

}

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package com.xu.test;

import java.io.File;

import java.io.FileOutputStream;

import org.objectweb.asm.ClassReader;

import org.objectweb.asm.ClassVisitor;

import org.objectweb.asm.ClassWriter;

/**

 * @author Administrator

 */

public class Test {

    public static void main(String[] args) throws Exception {

        ClassReader reader = new ClassReader("com/xu/test/Main");

        ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_MAXS);

        // 处理

        ClassVisitor visitor = new CustomerClassVisitor(writer);

        reader.accept(visitor, ClassReader.SKIP_DEBUG);

        // 输出

        File file = new File("target\\classes\\com\\xu\\test\\Main.class");

        FileOutputStream stream = new FileOutputStream(file);

        stream.write(writer.toByteArray());

        stream.close();

        // 测试

        Class<?> cls = Class.forName("com.xu.test.Main");

        Main main = (Main) cls.getDeclaredConstructor().newInstance();

        main.print();

    }

}