├── .gitignore ├── LICENSE ├── README.md ├── agent ├── pom.xml └── src │ └── main │ └── java │ └── me │ └── ivanyu │ └── javaagentsdemo │ ├── ClassListingTransformer.java │ ├── MetricsCollectionByteBuddyAgent.java │ ├── MetricsCollectionJavassistAgent.java │ ├── MetricsCollectionTransformer.java │ └── SimplestAgent.java ├── client ├── pom.xml └── src │ └── main │ └── java │ └── me │ └── ivanyu │ └── javaagentsdemo │ └── client │ └── ClientMain.java ├── common ├── pom.xml └── src │ └── main │ └── java │ └── me │ └── ivanyu │ └── javaagentsdemo │ └── common │ ├── CollectMetrics.java │ └── MetricsCollector.java └── pom.xml /.gitignore: -------------------------------------------------------------------------------- 1 | # Compiled class file 2 | *.class 3 | 4 | # Log file 5 | *.log 6 | 7 | # BlueJ files 8 | *.ctxt 9 | 10 | # Mobile Tools for Java (J2ME) 11 | .mtj.tmp/ 12 | 13 | # Package Files # 14 | *.jar 15 | *.war 16 | *.ear 17 | *.zip 18 | *.tar.gz 19 | *.rar 20 | 21 | # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml 22 | hs_err_pid* 23 | 24 | # Intellij IDEA 25 | .idea/ 26 | *.iml 27 | 28 | 29 | target/ -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright {yyyy} {name of copyright owner} 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # java-agents-demo 2 | 3 | **What:** An example of bytecode modifying Java agents done with Javassist and Byte Buddy. 4 | 5 | **More details** are in [this blog post](https://ivanyu.me/blog/2017/11/04/java-agents-javassist-and-byte-buddy/). 6 | -------------------------------------------------------------------------------- /agent/pom.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 6 | 7 | 4.0.0 8 | 9 | 10 | me.ivanyu.javaagentsdemo 11 | parent 12 | 1.0.0-SNAPSHOT 13 | ../pom.xml 14 | 15 | 16 | agent 17 | 1.0.0-SNAPSHOT 18 | agent 19 | Java Agents demo agent project 20 | 21 | jar 22 | 23 | 24 | 25 | 26 | me.ivanyu.javaagentsdemo.MetricsCollectionByteBuddyAgent 27 | 28 | 29 | 30 | 31 | me.ivanyu.javaagentsdemo 32 | common 33 | 1.0.0-SNAPSHOT 34 | 35 | 36 | 37 | org.javassist 38 | javassist 39 | 3.21.0-GA 40 | 41 | 42 | 43 | net.bytebuddy 44 | byte-buddy 45 | 1.7.8 46 | 47 | 48 | 49 | 50 | 51 | 52 | org.apache.maven.plugins 53 | maven-jar-plugin 54 | 2.4 55 | 56 | 57 | 58 | ${agent.class} 59 | ${agent.class} 60 | false 61 | false 62 | false 63 | 64 | 65 | 66 | 67 | 68 | 69 | maven-shade-plugin 70 | 3.1.0 71 | 72 | 73 | package 74 | 75 | shade 76 | 77 | 78 | 79 | 80 | 81 | 82 | 83 | 84 | -------------------------------------------------------------------------------- /agent/src/main/java/me/ivanyu/javaagentsdemo/ClassListingTransformer.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo; 2 | 3 | import java.lang.instrument.ClassFileTransformer; 4 | import java.security.ProtectionDomain; 5 | 6 | public class ClassListingTransformer implements ClassFileTransformer { 7 | @Override 8 | public byte[] transform(final ClassLoader loader, 9 | final String className, 10 | final Class classBeingRedefined, 11 | final ProtectionDomain protectionDomain, 12 | final byte[] classfileBuffer) { 13 | System.out.println(className); 14 | 15 | // null means "use the bytecode without modifications". 16 | return null; 17 | } 18 | } -------------------------------------------------------------------------------- /agent/src/main/java/me/ivanyu/javaagentsdemo/MetricsCollectionByteBuddyAgent.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo; 2 | 3 | import me.ivanyu.javaagentsdemo.common.CollectMetrics; 4 | import me.ivanyu.javaagentsdemo.common.MetricsCollector; 5 | import net.bytebuddy.agent.builder.AgentBuilder; 6 | import net.bytebuddy.agent.builder.AgentBuilder.Transformer; 7 | import net.bytebuddy.asm.Advice; 8 | import net.bytebuddy.asm.AsmVisitorWrapper; 9 | import net.bytebuddy.description.type.TypeDescription; 10 | import net.bytebuddy.dynamic.DynamicType; 11 | import net.bytebuddy.matcher.ElementMatchers; 12 | import net.bytebuddy.utility.JavaModule; 13 | 14 | import java.lang.instrument.Instrumentation; 15 | import java.lang.reflect.Executable; 16 | 17 | public class MetricsCollectionByteBuddyAgent { 18 | public static void premain(final String agentArgs, 19 | final Instrumentation inst) throws Exception { 20 | System.out.printf("Starting %s\n", 21 | MetricsCollectionByteBuddyAgent.class.getSimpleName()); 22 | 23 | new AgentBuilder.Default() 24 | .type(ElementMatchers.any()) 25 | .transform(new MetricsTransformer()) 26 | // .with(AgentBuilder.Listener.StreamWriting.toSystemOut()) 27 | .with(AgentBuilder.TypeStrategy.Default.REDEFINE) 28 | .installOn(inst); 29 | } 30 | 31 | private static class MetricsTransformer implements Transformer { 32 | @Override 33 | public DynamicType.Builder transform( 34 | final DynamicType.Builder builder, 35 | final TypeDescription typeDescription, 36 | final ClassLoader classLoader, 37 | final JavaModule module) { 38 | 39 | final AsmVisitorWrapper methodsVisitor = 40 | Advice.to(EnterAdvice.class, ExitAdviceMethods.class) 41 | .on(ElementMatchers.isAnnotatedWith(CollectMetrics.class) 42 | .and(ElementMatchers.isMethod())); 43 | 44 | final AsmVisitorWrapper constructorsVisitor = 45 | Advice.to(EnterAdvice.class, ExitAdviceConstructors.class) 46 | .on(ElementMatchers.isAnnotatedWith(CollectMetrics.class) 47 | .and(ElementMatchers.isConstructor())); 48 | 49 | return builder.visit(methodsVisitor).visit(constructorsVisitor); 50 | } 51 | 52 | private static class EnterAdvice { 53 | @Advice.OnMethodEnter 54 | static long enter() { 55 | return System.nanoTime(); 56 | } 57 | } 58 | 59 | private static class ExitAdviceMethods { 60 | @Advice.OnMethodExit(onThrowable = Throwable.class) 61 | static void exit(@Advice.Origin final Executable executable, 62 | @Advice.Enter final long startTime) { 63 | final long duration = System.nanoTime() - startTime; 64 | MetricsCollector.report(executable.toGenericString(), duration); 65 | } 66 | } 67 | 68 | private static class ExitAdviceConstructors { 69 | @Advice.OnMethodExit 70 | static void exit(@Advice.Origin final Executable executable, 71 | @Advice.Enter final long startTime) { 72 | final long duration = System.nanoTime() - startTime; 73 | MetricsCollector.report(executable.toGenericString(), duration); 74 | } 75 | } 76 | } 77 | } 78 | -------------------------------------------------------------------------------- /agent/src/main/java/me/ivanyu/javaagentsdemo/MetricsCollectionJavassistAgent.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo; 2 | 3 | import java.lang.instrument.Instrumentation; 4 | 5 | public class MetricsCollectionJavassistAgent { 6 | public static void premain(final String agentArgs, 7 | final Instrumentation inst) throws Exception { 8 | System.out.printf("Starting %s\n", 9 | MetricsCollectionJavassistAgent.class.getSimpleName()); 10 | inst.addTransformer(new MetricsCollectionTransformer()); 11 | } 12 | } 13 | -------------------------------------------------------------------------------- /agent/src/main/java/me/ivanyu/javaagentsdemo/MetricsCollectionTransformer.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo; 2 | 3 | import javassist.*; 4 | import javassist.bytecode.AnnotationsAttribute; 5 | import javassist.bytecode.MethodInfo; 6 | import javassist.bytecode.annotation.Annotation; 7 | import me.ivanyu.javaagentsdemo.common.CollectMetrics; 8 | import me.ivanyu.javaagentsdemo.common.MetricsCollector; 9 | 10 | import java.lang.instrument.ClassFileTransformer; 11 | import java.lang.instrument.IllegalClassFormatException; 12 | import java.security.ProtectionDomain; 13 | 14 | public class MetricsCollectionTransformer implements ClassFileTransformer { 15 | 16 | private final ClassPool classPool = ClassPool.getDefault(); 17 | 18 | @Override 19 | public byte[] transform(final ClassLoader loader, 20 | final String className, 21 | final Class classBeingRedefined, 22 | final ProtectionDomain protectionDomain, 23 | final byte[] classfileBuffer) 24 | throws IllegalClassFormatException { 25 | 26 | // className can be null, ignoring such classes. 27 | if (className == null) { 28 | return null; 29 | } 30 | 31 | // Javassist uses "." as a separator in class/package names. 32 | final String classNameDots = className.replaceAll("/", "."); 33 | final CtClass ctClass = classPool.getOrNull(classNameDots); 34 | 35 | // Won't find some classes from java.lang.invoke, 36 | // but we're not interested in them anyway. 37 | if (ctClass == null) { 38 | return null; 39 | } 40 | 41 | // A frozen CtClass is a CtClass 42 | // that was already converted to Java class. 43 | if (ctClass.isFrozen()) { 44 | // No longer need to keep the CtClass object in memory. 45 | ctClass.detach(); 46 | return null; 47 | } 48 | 49 | try { 50 | boolean anyMethodInstrumented = false; 51 | 52 | // Behaviors == methods and constructors. 53 | for (final CtBehavior behavior : ctClass.getDeclaredBehaviors()) { 54 | if (isAnnotatedAsCollectMetrics(behavior)) { 55 | System.out.printf("%s - will collect metrics\n", 56 | behavior.getLongName()); 57 | instrument(behavior); 58 | anyMethodInstrumented = true; 59 | } 60 | } 61 | 62 | if (anyMethodInstrumented) { 63 | return ctClass.toBytecode(); 64 | } 65 | } catch (Exception e) { 66 | e.printStackTrace(System.err); 67 | } finally { 68 | // No longer need to keep the CtClass object in memory. 69 | ctClass.detach(); 70 | } 71 | 72 | return null; 73 | } 74 | 75 | /** 76 | * Checks if the behavior is annotated with @CollectMetrics. 77 | */ 78 | private boolean isAnnotatedAsCollectMetrics(final CtBehavior behavior) { 79 | final MethodInfo methodInfo = behavior.getMethodInfo(); 80 | 81 | for (final Object attrInfo : methodInfo.getAttributes()) { 82 | if (attrInfo instanceof AnnotationsAttribute) { 83 | final Annotation annotation = ((AnnotationsAttribute) attrInfo) 84 | .getAnnotation(CollectMetrics.class.getName()); 85 | return annotation != null; 86 | } 87 | } 88 | 89 | return false; 90 | } 91 | 92 | /** 93 | * Instruments the behavior with metric reporting code. 94 | */ 95 | private void instrument(final CtBehavior behavior) 96 | throws CannotCompileException, NotFoundException { 97 | 98 | behavior.addLocalVariable("$_traceTimeStart", CtClass.longType); 99 | behavior.insertBefore("$_traceTimeStart = System.nanoTime();"); 100 | 101 | // Add reporting of the call, e.g.: 102 | // MetricsCollector.report("", 1256); 103 | // Won't work in case of exception. 104 | final String reportCode = MetricsCollector.class.getName() + 105 | ".report(" + 106 | "\"" + behavior.getLongName() + "\", " + 107 | "System.nanoTime() - $_traceTimeStart" + 108 | ");"; 109 | behavior.insertAfter(reportCode); 110 | } 111 | } 112 | -------------------------------------------------------------------------------- /agent/src/main/java/me/ivanyu/javaagentsdemo/SimplestAgent.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo; 2 | 3 | import java.lang.instrument.Instrumentation; 4 | 5 | public class SimplestAgent { 6 | /** 7 | * If the agent is attached to a JVM on the start, 8 | * this method is invoked before {@code main} method is called. 9 | * 10 | * @param agentArgs Agent command line arguments. 11 | * @param inst An object to access the JVM instrumentation mechanism. 12 | */ 13 | public static void premain(final String agentArgs, 14 | final Instrumentation inst) { 15 | System.out.println( 16 | "Hey, look: I'm instrumenting a freshly started JVM!"); 17 | } 18 | 19 | /** 20 | * If the agent is attached to an already running JVM, 21 | * this method is invoked. 22 | * 23 | * @param agentArgs Agent command line arguments. 24 | * @param inst An object to access the JVM instrumentation mechanism. 25 | */ 26 | public static void agentmain(final String agentArgs, 27 | final Instrumentation inst) { 28 | System.out.println("Hey, look: I'm instrumenting a running JVM!"); 29 | } 30 | } 31 | -------------------------------------------------------------------------------- /client/pom.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 6 | 7 | 4.0.0 8 | 9 | 10 | me.ivanyu.javaagentsdemo 11 | parent 12 | 1.0.0-SNAPSHOT 13 | ../pom.xml 14 | 15 | 16 | client 17 | 1.0.0-SNAPSHOT 18 | client 19 | Java Agents demo client project 20 | 21 | jar 22 | 23 | 24 | 25 | me.ivanyu.javaagentsdemo 26 | common 27 | 1.0.0-SNAPSHOT 28 | 29 | 30 | 31 | 32 | 33 | 34 | org.apache.maven.plugins 35 | maven-jar-plugin 36 | 3.0.2 37 | 38 | 39 | 40 | me.ivanyu.javaagentsdemo.client.ClientMain 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | -------------------------------------------------------------------------------- /client/src/main/java/me/ivanyu/javaagentsdemo/client/ClientMain.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo.client; 2 | 3 | import me.ivanyu.javaagentsdemo.common.CollectMetrics; 4 | import me.ivanyu.javaagentsdemo.common.MetricsCollector; 5 | 6 | public class ClientMain { 7 | public static void main(String[] args) throws InterruptedException { 8 | final Adder adder = new Adder(); 9 | for (int i = 0; i < 10; i++) { 10 | helloWorld(); 11 | adder.add(1, 30); 12 | } 13 | 14 | try { 15 | withException(); 16 | } catch (Exception e) { 17 | // do nothing 18 | } 19 | 20 | MetricsCollector.getEntries().forEach((key, entry) -> { 21 | System.out.printf("%s\t%d calls\t%d ns avg\n", 22 | key, entry.getCallCounts(), entry.getAvgDuration()); 23 | }); 24 | } 25 | 26 | @CollectMetrics 27 | private static void helloWorld() throws InterruptedException { 28 | System.out.println("Hello world"); 29 | Thread.sleep(124L); 30 | } 31 | 32 | @CollectMetrics 33 | private static void withException() throws Exception { 34 | throw new Exception(); 35 | } 36 | 37 | private static class Adder { 38 | @CollectMetrics // applicable to constructor as well 39 | Adder() throws InterruptedException { 40 | Thread.sleep(1234L); 41 | } 42 | 43 | @CollectMetrics 44 | public int add(final int a, final int b) { 45 | return a + b; 46 | } 47 | } 48 | } 49 | -------------------------------------------------------------------------------- /common/pom.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 6 | 7 | 4.0.0 8 | 9 | 10 | me.ivanyu.javaagentsdemo 11 | parent 12 | 1.0.0-SNAPSHOT 13 | ../pom.xml 14 | 15 | 16 | common 17 | 1.0.0-SNAPSHOT 18 | common 19 | Java Agents demo common classes 20 | 21 | jar 22 | 23 | 24 | 25 | 26 | -------------------------------------------------------------------------------- /common/src/main/java/me/ivanyu/javaagentsdemo/common/CollectMetrics.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo.common; 2 | 3 | import java.lang.annotation.*; 4 | 5 | @Target({ElementType.METHOD, ElementType.CONSTRUCTOR}) 6 | @Retention(RetentionPolicy.RUNTIME) 7 | public @interface CollectMetrics { 8 | } 9 | -------------------------------------------------------------------------------- /common/src/main/java/me/ivanyu/javaagentsdemo/common/MetricsCollector.java: -------------------------------------------------------------------------------- 1 | package me.ivanyu.javaagentsdemo.common; 2 | 3 | import java.util.Collections; 4 | import java.util.Map; 5 | import java.util.concurrent.ConcurrentHashMap; 6 | 7 | /** 8 | * Collects metrics on method calls. 9 | * 10 | * Counts the total number of method calls and 11 | * the average duration of method execution (with Exponential moving average 12 | * https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average). 13 | */ 14 | public class MetricsCollector { 15 | private static final 16 | ConcurrentHashMap entries = new ConcurrentHashMap<>(); 17 | 18 | private static final double alpha = 0.015; 19 | 20 | /** 21 | * Report method call metrics. 22 | */ 23 | public static void report(final String methodName, 24 | final long duration) { 25 | 26 | entries.compute(methodName, 27 | (final String key, 28 | final Entry curr) -> { 29 | if (curr == null) { 30 | return new Entry(1L, duration); 31 | } 32 | 33 | final long newAvgDuration = Math.round( 34 | curr.getAvgDuration() * (1 - alpha) + duration * alpha); 35 | return new Entry( 36 | curr.getCallCounts() + 1, newAvgDuration); 37 | }); 38 | } 39 | 40 | public static class Entry { 41 | private final long callCounts; 42 | private final long avgDuration; 43 | 44 | private Entry(final long callCounts, final long avgDuration) { 45 | this.callCounts = callCounts; 46 | this.avgDuration = avgDuration; 47 | } 48 | 49 | public long getCallCounts() { 50 | return callCounts; 51 | } 52 | 53 | public long getAvgDuration() { 54 | return avgDuration; 55 | } 56 | } 57 | 58 | public static Map getEntries() { 59 | return Collections.unmodifiableMap(entries); 60 | } 61 | } 62 | -------------------------------------------------------------------------------- /pom.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 6 | 7 | 4.0.0 8 | 9 | me.ivanyu.javaagentsdemo 10 | parent 11 | 1.0.0-SNAPSHOT 12 | parent 13 | Java Agents demo parent POM 14 | 15 | 16 | UTF-8 17 | 18 | 19 | 20 | 21 | Apache License, Version 2.0 22 | https://www.apache.org/licenses/LICENSE-2.0.txt 23 | repo 24 | A business-friendly OSS license 25 | 26 | 27 | 28 | 29 | 30 | ivanyu 31 | Ivan Yurchenko 32 | ivan0yurchenko@gmail.com 33 | 34 | 35 | 36 | pom 37 | 38 | https://github.com/ivanyu/java-agents-demo 39 | 40 | 41 | common 42 | agent 43 | client 44 | 45 | 46 | 47 | 48 | 49 | org.apache.maven.plugins 50 | maven-compiler-plugin 51 | 3.7.0 52 | 53 | 1.8 54 | 1.8 55 | 56 | 57 | 58 | 59 | 60 | 61 | --------------------------------------------------------------------------------