利用javaagent,javassist 进行热修补

使用命令:

java -javaagent:agent.jar -jar target.jar

注意事项: 

1. -javaagent:agent.jar "-javaagent:"后面没有空格,紧接着的是agent.jar
2. javaagent资料可以google. 

agent.jar注意事项

• MANIFEST.MF文件内容
  

  Manifest-Version: 1.0
  Premain-Class: com.xiaobai.Main
  Can-Redefine-Classes: true

注意每个":" 后面都有一个空格,不加报错

• 外部jar引用注意. 
  要打包进agent.jar,不要以jar形式存在,否则报错找不到class文件

javassist资料不介绍了,网上很多.

例子:

• Mian.java
  

  package com.xiaobai;
  
  import java.lang.instrument.Instrumentation;
  
  public class Main {
      public static void premain(String agentOps, Instrumentation inst) {
          inst.addTransformer(new NewTransformer());
      }
  }
  

  　　

• NewTransformer.java
  

  package com.xiaobai;
  
  import javassist.*;
  
  import java.io.ByteArrayInputStream;
  import java.io.IOException;
  import java.lang.instrument.ClassFileTransformer;
  import java.lang.instrument.IllegalClassFormatException;
  
  import java.security.ProtectionDomain;
  
  /**
   * description: Transformer
   * author: xiaobai
   * data: 2016/8/30
   */
  public class NewTransformer implements ClassFileTransformer {
  
  
      @Override
      public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
          className = className.replace("/", ".");
          if (!className.equals("com.pnfsoftware.jeb.client.AbstractClientContext"))return null;
          try {
              ClassPool classPool=ClassPool.getDefault();
              ByteArrayInputStream byteArrayInputStream=new ByteArrayInputStream(classfileBuffer);
              CtClass clazz=classPool.makeClass(byteArrayInputStream);
              CtMethod[] methods=clazz.getMethods();
              for (CtMethod method:methods){
                  if (method.getName().equals("ping")){
                      return fixMethod(clazz,method.getName());
                  }
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
          return new byte[0];
      }
      private byte[] fixMethod(CtClass clazz,String oldmethodName){
          try {
              CtMethod method=clazz.getDeclaredMethod(oldmethodName);
              StringBuilder bodyStr = new StringBuilder();
              bodyStr.append("{");
              bodyStr.append("System.out.println(\"开始热补丁\");\n");
              bodyStr.append("return 0;");
              bodyStr.append("}");
              method.setBody(bodyStr.toString());
              return clazz.toBytecode();
          } catch (NotFoundException e) {
              e.printStackTrace();
          } catch (CannotCompileException e) {
              e.printStackTrace();
          } catch (IOException e) {
              e.printStackTrace();
          }
  
          return null;
      }
  
  }

效果图: