javassist简介

Javassist是一个开源的分析、编辑和创建Java字节码的类库。

demo目的给一个字节码里面的构造方法添加一个输出语句

• 待添加的java类

package com.suse.yuxin;
public class User {
    private String userName;
    private String userNumber;
    
    public User(String userName, String userNumber) {
        super();
        this.userName = userName;
        this.userNumber = userNumber;
    }
    
  }

• 测试代码

public class TestAssist {
    public static void main(String args[]) throws NotFoundException, CannotCompileException, IOException{
        ClassPool pool = ClassPool.getDefault();
        //设置classPath
        pool.appendClassPath("D:\\javaworkspace\\Test\\bin");
        //获取一个class文件
        CtClass ctClass = pool.get("com.suse.yuxin.User");
        //获取构造方法
        CtConstructor ctConstructor = ctClass.getConstructors()[0];
        //插入输出语句
        ctConstructor.insertAfter("System.out.println();");
        ctClass.writeFile("D:\\javaworkspace\\Test\\bin\\output");
        System.out.println("OK");
    }
    
    }

• 反编译查看

  
  

工具

• javassist jar 包使用的是3.9.0
• 反编译使用的工具是 jd-gui

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