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songlonqi-javasonglonqi-java
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agent example
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‎.gitignore‎

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target
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dependency-reduced-pom.xml
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/.metadata/
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/.recommenders/
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.classpath
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.project
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.settings
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.idea/
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*.iml
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.DS_Store
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html_docs
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docs/html/
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**/__pycache__/
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.m2/
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fetch.log
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.ci/.aws

‎pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>javaagent-examples</groupId>
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<artifactId>javaagent-examples</artifactId>
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<name>javaagent-examples</name>
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<version>1.0</version>
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<description>javaagent-examples</description>
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<packaging>jar</packaging>
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<build>
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<finalName>javaagent-examples</finalName>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<configuration>
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<source>1.6</source>
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<target>1.6</target>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-assembly-plugin</artifactId>
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<executions>
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<execution>
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<goals>
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<goal>attached</goal>
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</goals>
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<phase>package</phase>
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<configuration>
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<descriptorRefs>
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<descriptorRef>jar-with-dependencies</descriptorRef>
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</descriptorRefs>
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<archive>
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<manifest>
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<mainClass>name.dhruba.javaagent.MyMainClass</mainClass>
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</manifest>
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<manifestEntries>
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<Premain-Class>name.dhruba.javaagent.MyJavaAgent</Premain-Class>
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<Agent-Class>name.dhruba.javaagent.MyJavaAgent</Agent-Class>
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<Can-Redefine-Classes>true</Can-Redefine-Classes>
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<Can-Retransform-Classes>true</Can-Retransform-Classes>
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</manifestEntries>
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</archive>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.7</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>asm</groupId>
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<artifactId>asm</artifactId>
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<version>3.2</version>
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</dependency>
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<dependency>
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<groupId>com.sun</groupId>
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<artifactId>tools</artifactId>
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<version>1.6.0</version>
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<scope>system</scope>
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<systemPath>${java.home}/../lib/tools.jar</systemPath>
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</dependency>
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<dependency>
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<groupId>org.slf4j</groupId>
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<artifactId>jcl-over-slf4j</artifactId>
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<version>1.5.8</version>
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<scope>runtime</scope>
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</dependency>
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<dependency>
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<groupId>ch.qos.logback</groupId>
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<artifactId>logback-classic</artifactId>
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<version>0.9.9</version>
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</dependency>
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</dependencies>
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</project>

‎src/main/java/name/dhruba/javaagent/MyClassFileTransformer.java‎

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package name.dhruba.javaagent;
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import java.lang.instrument.ClassFileTransformer;
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import java.lang.instrument.IllegalClassFormatException;
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import java.security.ProtectionDomain;
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import org.objectweb.asm.ClassWriter;
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import org.objectweb.asm.Label;
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import org.objectweb.asm.MethodVisitor;
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import org.objectweb.asm.Opcodes;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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public class MyClassFileTransformer implements ClassFileTransformer, Opcodes {
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static final Logger logger = LoggerFactory.getLogger(MyClassFileTransformer.class);
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@Override
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public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
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ProtectionDomain protectionDomain, byte[] classfileBuffer)
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throws IllegalClassFormatException {
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logger.info("class file transformer invoked for className: {}", className);
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if (className.equals("name/dhruba/user/MyUser")) {
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ClassWriter cw = new ClassWriter(0);
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MethodVisitor mv;
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cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "name/dhruba/user/MyUser", null,
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"java/lang/Object", null);
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cw.visitSource(null, null);
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{
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mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
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mv.visitCode();
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Label l0 = new Label();
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mv.visitLabel(l0);
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mv.visitLineNumber(3, l0);
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mv.visitVarInsn(ALOAD, 0);
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mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
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mv.visitInsn(RETURN);
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Label l1 = new Label();
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mv.visitLabel(l1);
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mv.visitLocalVariable("this", "Lname/dhruba/user/MyUser;", null, l0, l1, 0);
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mv.visitMaxs(1, 1);
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mv.visitEnd();
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}
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{
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mv = cw.visitMethod(ACC_PUBLIC, "getName", "()Ljava/lang/String;", null, null);
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mv.visitCode();
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Label l0 = new Label();
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mv.visitLabel(l0);
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mv.visitLineNumber(6, l0);
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mv.visitLdcInsn("bar");
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mv.visitInsn(ARETURN);
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Label l1 = new Label();
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mv.visitLabel(l1);
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mv.visitLocalVariable("this", "Lname/dhruba/user/MyUser;", null, l0, l1, 0);
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mv.visitMaxs(1, 1);
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mv.visitEnd();
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}
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cw.visitEnd();
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return cw.toByteArray();
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}
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return classfileBuffer;
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}
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}

‎src/main/java/name/dhruba/javaagent/MyJavaAgent.java‎

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package name.dhruba.javaagent;
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import java.lang.instrument.Instrumentation;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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public class MyJavaAgent {
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static final Logger logger = LoggerFactory.getLogger(MyJavaAgent.class);
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private static Instrumentation instrumentation;
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/**
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* JVM hook to statically load the javaagent at startup.
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*
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* After the Java Virtual Machine (JVM) has initialized, the premain method
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* will be called. Then the real application main method will be called.
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*
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* @param args
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* @param inst
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* @throws Exception
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*/
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public static void premain(String args, Instrumentation inst) throws Exception {
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logger.info("premain method invoked with args: {} and inst: {}", args, inst);
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instrumentation = inst;
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instrumentation.addTransformer(new MyClassFileTransformer());
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}
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/**
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* JVM hook to dynamically load javaagent at runtime.
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*
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* The agent class may have an agentmain method for use when the agent is
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* started after VM startup.
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*
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* @param args
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* @param inst
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* @throws Exception
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*/
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public static void agentmain(String args, Instrumentation inst) throws Exception {
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logger.info("agentmain method invoked with args: {} and inst: {}", args, inst);
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instrumentation = inst;
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instrumentation.addTransformer(new MyClassFileTransformer());
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}
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/**
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* Programmatic hook to dynamically load javaagent at runtime.
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*/
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public static void initialize() {
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if (instrumentation == null) {
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MyJavaAgentLoader.loadAgent();
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}
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}
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}

‎src/main/java/name/dhruba/javaagent/MyJavaAgentLoader.java‎

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package name.dhruba.javaagent;
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import java.lang.management.ManagementFactory;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import com.sun.tools.attach.VirtualMachine;
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public class MyJavaAgentLoader {
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static final Logger logger = LoggerFactory.getLogger(MyJavaAgentLoader.class);
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private static final String jarFilePath = "/home/dhruba/.m2/repository/"
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+ "javaagent-examples/javaagent-examples/1.0/"
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+ "javaagent-examples-1.0-jar-with-dependencies.jar";
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public static void loadAgent() {
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logger.info("dynamically loading javaagent");
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String nameOfRunningVM = ManagementFactory.getRuntimeMXBean().getName();
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int p = nameOfRunningVM.indexOf('@');
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String pid = nameOfRunningVM.substring(0, p);
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try {
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VirtualMachine vm = VirtualMachine.attach(pid);
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vm.loadAgent(jarFilePath, "");
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vm.detach();
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} catch (Exception e) {
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throw new RuntimeException(e);
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}
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}
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}

‎src/main/java/name/dhruba/javaagent/MyMainClass.java‎

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package name.dhruba.javaagent;
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import java.util.Arrays;
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import name.dhruba.user.MyUser;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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public class MyMainClass {
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static final Logger logger = LoggerFactory.getLogger(MyMainClass.class);
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static {
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MyJavaAgent.initialize();
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}
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/**
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* Main method.
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*
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* @param args
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*/
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public static void main(String[] args) {
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logger.info("main method invoked with args: {}", Arrays.asList(args));
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logger.info("userName: {}", new MyUser().getName());
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}
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}

‎src/main/java/name/dhruba/user/MyUser.java‎

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package name.dhruba.user;
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public class MyUser {
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public String getName() {
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return "foo";
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}
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}

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