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javaagent学习_java agent学习

作者：黑客灵魂 | 2024-07-25 09:48:30

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java agent学习

<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.study</groupId>
   <artifactId>instrustment</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <dependencies>

       <dependency>
           <groupId>org.apache.bcel</groupId>
           <artifactId>bcel</artifactId>
           <version>6.2</version>
       </dependency>
       
       <dependency>
           <groupId>org.javassist</groupId>
           <artifactId>javassist</artifactId>
           <version>3.19.0-GA</version>
       </dependency>

   </dependencies>
   <build>
       <plugins>
           <plugin>
               <groupId>com.rimerosolutions.maven.plugins</groupId>
               <artifactId>wrapper-maven-plugin</artifactId>
               <version>0.0.4</version>
           </plugin>
           <plugin>
               <groupId>org.apache.maven.plugins</groupId>
               <artifactId>maven-compiler-plugin</artifactId>
               <configuration>
                   <encoding>UTF-8</encoding>
                   <source>1.8</source>
                   <target>1.8</target>
                   <compilerArguments>
                       <verbose />
                       <bootclasspath>${java.home}/lib/rt.jar</bootclasspath>
                   </compilerArguments>
               </configuration>
           </plugin>
       </plugins>
   </build>

</project>

public class MyMain {

public static void main(String args[]) {
myTest();

}

   private static void myTest() {
       try {
           Thread.currentThread().sleep(3000);
       } catch (InterruptedException e) {
           e.printStackTrace();
       }
   }

}

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;

public class PerfMonAgent {
private static Instrumentation inst = null;

   public static void premain(String agentArgs, Instrumentation _inst) {
       System.out.println("PerfMonAgent.premain() was called.");
       inst = _inst;
       ClassFileTransformer trans = new PerfMonXformer();
       System.out.println("Adding a PerfMonXformer instance to the JVM.");
       inst.addTransformer(trans);
   }
}

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

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtBehavior;
import javassist.CtClass;
import javassist.NotFoundException;

public class PerfMonXformer implements ClassFileTransformer {
   public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
           ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
       byte[] transformed = null;
//       System.out.println("Transforming " + className);
       ClassPool pool = ClassPool.getDefault();
       CtClass cl = null;
       try {
           cl = pool.makeClass(new java.io.ByteArrayInputStream(classfileBuffer));
           if (cl.isInterface() == false) {
               CtBehavior[] methods = cl.getDeclaredBehaviors();
               for (int i = 0; i < methods.length; i++) {
                   if (methods[i].isEmpty() == false) {
                       doMethod(methods[i]);
                   }
               }
               transformed = cl.toBytecode();
           }
       } catch (Exception e) {
           System.err.println("Could not instrument " + className + ", exception : " + e.getMessage());
       } finally {
           if (cl != null) {
               cl.detach();
           }
       }
       return transformed;
   }

   private void doMethod(CtBehavior method) throws NotFoundException, CannotCompileException {
       if ("myTest".equalsIgnoreCase(method.getName())) {
           // 添加局部变量，如果不同过addLocalVariable设置，在调用属性时将出现compile error: no such field:
           // startTime
           method.addLocalVariable("startTime", CtClass.longType);
           method.insertBefore("System.out.println(startTime);");
           method.insertBefore("startTime = System.currentTimeMillis();");
//           method.insertBefore("long startTime = System.currentTimeMillis();System.out.println(startTime);");
           method.insertBefore("System.out.println(\"insert before ......\");");
           method.insertAfter("System.out.println(\"leave " + method.getName()
                   + " and time is :\"+System.currentTimeMillis()+\":\" + (System.currentTimeMillis() - startTime));");
       }
   }

}

java -cp /home/your_home/.m2/repository/org/javassist/javassist/3.19.0-GA/javassist-3.19.0-GA.jar:./ -javaagent:/yourpath/target/PerMonAgent.jar MyMain

----------------

MANIFEST.MF

Manifest-Version: 1.0
Premain-Class: PerfMonAgent
Can-Redefine-Classes: true

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