基于Java Agent的premain方式实现方法耗时监控问题

public class MyAgentTest {
    public static void main(String[] args) throws InterruptedException {
        MyAgentTest mat = new MyAgentTest();
        mat.test();
        Thread.sleep((long)(Math.random() * 10));//随机暂停0-10ms
    }

    public void test() throws InterruptedException {
        System.out.println("I'm TestAgent");
        Thread.sleep((long)(Math.random() * 100));//随机暂停0-100ms
    }
}

myagent
├── pom.xml
├── src
│   └── main
│       ├── java
│       │   └── test
│       │       ├── MyAgent.java
│       │       └── MyTransformer.java
│       └── resources
│           └── META-INF
│               └── MANIFEST.MF

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.hebh.me</groupId>
  <artifactId>demo-myagent</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>demo-myagent Maven Webapp</name>
  <url>http://www.example.com</url>

  <dependencies>
    <dependency>
      <groupId>javassist</groupId>
      <artifactId>javassist</artifactId>
      <version>3.12.1.GA</version>
    </dependency>
  </dependencies>

  <build>
    <finalName>myagent</finalName>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>
          <archive>
            <!--避免MANIFEST.MF被覆盖-->
            <manifestFile>src/main/resources/META-INF/MANIFEST.MF</manifestFile>
          </archive>
          <descriptorRefs>
            <!--打包时加入依赖-->
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

package test;

import java.lang.instrument.Instrumentation;
public class MyAgent {
    public static void premain(String args, Instrumentation inst){
        System.out.println("Hi, I'm agent!");
        inst.addTransformer(new MyTransformer());
    }
}

package test;

import java.lang.instrument.ClassFileTransformer;
import java.security.ProtectionDomain;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;

/**
 * 检测方法的执行时间
 */
public class MyTransformer implements ClassFileTransformer {

    final static String prefix = "\nlong startTime = System.currentTimeMillis();\n";
    final static String postfix = "\nlong endTime = System.currentTimeMillis();\n";

    @Override
    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
                            ProtectionDomain protectionDomain, byte[] classfileBuffer){
        //java自带的方法不进行处理
        if(className.startsWith("java") || className.startsWith("sun")){
            return null;
        }
        className = className.replace("/", ".");
        CtClass ctclass = null;
        try {
            ctclass = ClassPool.getDefault().get(className);// 使用全称,用于取得字节码类<使用javassist>
            for(CtMethod ctMethod : ctclass.getDeclaredMethods()){
                String methodName = ctMethod.getName();
                String newMethodName = methodName + "$old";// 新定义一个方法叫做比如sayHello$old
                ctMethod.setName(newMethodName);// 将原来的方法名字修改

                // 创建新的方法，复制原来的方法，名字为原来的名字
                CtMethod newMethod = CtNewMethod.copy(ctMethod, methodName, ctclass, null);

                // 构建新的方法体
                StringBuilder bodyStr = new StringBuilder();
                bodyStr.append("{");
                bodyStr.append("System.out.println(\"==============Enter Method: " + className + "." + methodName + " ==============\");");
                bodyStr.append(prefix);
                bodyStr.append(newMethodName + "($$);\n");// 调用原有代码，类似于method();($$)表示所有的参数
                bodyStr.append(postfix);
                bodyStr.append("System.out.println(\"==============Exit Method: " + className + "." + methodName + " Cost:\" +(endTime - startTime) +\"ms " + "===\");");
                bodyStr.append("}");

                newMethod.setBody(bodyStr.toString());// 替换新方法
                ctclass.addMethod(newMethod);// 增加新方法
            }
            return ctclass.toBytecode();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

Manifest-Version: 1.0
Created-By: 0.0.1 (Demo Inc.)
Premain-Class: test.MyAgent

mvn assembly:assembly

javac MyAgentTest.java