Use ByteBuddy and Instrument API for code redefinition(Java)

对 Arthas Redefine 功能的封装，通过 API 接口的方式上传修改后的 Java 文件，并自动编译，替换

使用方法

Maven Central Repository

<dependency>
  <groupId>io.github.bigwolftime</groupId>
  <artifactId>redefine</artifactId>
  <version>0.0.7</version>
</dependency>

以 Postman 为例：

@Bean
public ServletRegistrationBean servletRegistrationBean() {
   ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean();
   try {
      Class<?> extendRedefineServlet = Class.forName("com.bigwolftime.api.ExtendRedefineServlet");
      HttpServlet httpServlet = (HttpServlet) extendRedefineServlet.newInstance();
      servletRegistrationBean.setServlet(httpServlet);
      servletRegistrationBean.addUrlMappings("/backend/redefine/base64");
      return servletRegistrationBean;
   } catch (Exception e) {
      log.warn("not found ExtendRedefineServlet");
   }

   return null;
}

• 地址: projectDomain/backend/redefine/base64
• 请求方式: POST
• 参数

参数名	示例	备注
class	com.xx.yy.YourClass	要替换的全限定类名(即 package.YourClassName)
base64_file	base64 content	source code with base64 encode format

注意事项

1. 由于 JDK 限制，替换的新类对于原来的类，不能修改方法签名，不能新增/减少方法，否则会抛出异常 Attempted to add/delete a method； 不能新增/删除/修改类级别的成员变量，否则会抛出异常 attempted to change the schema (add/remove fields)；不能修改枚举类的内容
2. 向外暴露接口，需要考虑权限校验，项目中并没有相关实现

已知问题

1. 某些低版本 Tomcat 在应用启动时会报错:

SEVERE: Unable to process Jar entry [META-INF/versions/9/module-info.class] from Jar [jar:file:/WEB-INF/lib/byte-buddy-agent-1.9.3.jar!/] for annotations
org.apache.tomcat.util.bcel.classfile.ClassFormatException: Invalid byte tag in constant pool: 19
	at org.apache.tomcat.util.bcel.classfile.Constant.readConstant(Constant.java:136)
	at org.apache.tomcat.util.bcel.classfile.ConstantPool.<init>(ConstantPool.java:59)
	at org.apache.tomcat.util.bcel.classfile.ClassParser.readConstantPool(ClassParser.java:208)
	at org.apache.tomcat.util.bcel.classfile.ClassParser.parse(ClassParser.java:118)
	at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2055)
	at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:1931)
	at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1897)
	at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1882)
	at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1314)
	at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:873)
	at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:371)
	at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
	at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5355)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:632)
	at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1073)
	at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1857)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

可忽略. 其原因是自 Java9 引入了模块化, 且新版本的 ByteBuddy 使用了此特性，导致某些低版本 Tomcat 无法处理. 具体可见 此处1 此处2

---

MyNote:

1. GPG keys upload https://central.sonatype.org/pages/working-with-pgp-signatures.html#installing-gnupg

Server List

• hkp://keys.gnupg.net
• hkp://pool.sks-keyservers.net

2. mvn deploy occur: gpg: signing failed: Inappropriate ioctl for device

原因是 gpg 在当前终端无法弹出密码输入页面 export GPG_TTY=$(tty) ~/.bash_profile

reference: https://my.oschina.net/ujjboy/blog/3023151