Bytecode Manipulation with a Java Agent and Byte Buddy. Koichi Sakata PONOS Corporation

Transcription

1 Bytecode Manipulation with a Java Agent and Byte Buddy Koichi Sakata PONOS Corporation

2 2 About Me Koichi Sakata ( ) KanJava JUG Leader Java Champion PONOS Corporation

3 3

4 4 Intended Audience Those who want to start manipulating bytecode Not for experts

5 5 Q&A If you could, let's hold all the questions until the end

6 6 Java Bytecode.java Java Code javac.class Bytecode Gets loaded by JVM

7 7 What is bytecode manipulation? Editing bytecode in the class files Add Delete Replace

8 8 Why do we manipulate? It's fun!

9 9 Not Only Fun To change code at runtime Generate Entity objects in Hibernate Create mock objects in Mockito

10 10 Bytecode Manipulation Hard to manipulate by hand... A class file is a binary file JVM has a verification process

11 11 Bytecode Manipulation Libraries Byte Buddy Byteman Javassist cglib ASM Apache Commons BCEL

12 12 Byte Buddy Easy-to-use API Java 11 Support Duke's Choice Award 2015 Winner

13 13 Byte Buddy Usage in major libraries Hibernate Mockito Jackson etc.

14 14 Hello World in Byte Buddy Class<?> subclass = new ByteBuddy().subclass(Object.class).method(ElementMatchers.named("toString")).intercept(FixedValue.value("Hello World!")).make().load(getClass().getClassLoader()).getLoaded();

15 15 Hello World in Byte Buddy Class<?> subclass = new ByteBuddy().subclass(Object.class).method(ElementMatchers.named("toString")) 1. Create a subclass of Object 2. Choose the tostring()

16 16 Hello World in Byte Buddy.method(ElementMatchers.named("toString")).intercept(FixedValue.value("Hello World!")) 1. Intercept tostring() to return a fixed string value "Hello World"

17 17 Hello World in Byte Buddy.make().load(getClass().getClassLoader()).getLoaded(); 1. Make a new type (unloaded class) 2. Load the type 3. Get the new loaded class

18 18 Hello World in Byte Buddy Class<?> subclass = new ByteBuddy().subclass(Object.class).method(ElementMatchers.named("toString")).intercept(FixedValue.value("Hello World!")).make().load(getClass().getClassLoader()).getLoaded();

19 19 Demo 1 Run Hello World See a generated class

20 20 Demo code is available github.com/jyukutyo/samplecodeforbyt ebuddyseeesion

21 21 Usage in Mockito SubclassBytecodeGenerator mockclass()

22 22 How to use BM? 1. Directly in your application 2. At build time via Maven/Gradle 3. With Java Agent No need for changing code Detachable

23 23 Java Agent? Do espionage activities in your application Profiling Logging Changing the target application itself

24 24 Java Agent Instrument programs running on the JVM JSR 163: JavaTM Platform Profiling Architecture JVM calls Java Agent method with proper timing

25 25 Create a Java Agent Just define methods premain() Method agentmain() Method

26 26 Create a Java Agent premain() Method Gets called before main() method agentmain() Method Gets called when the agent is attached after JVM startup

27 27 With Java Agent We can run bytecode manipulation code at runtime

28 28

29 29 premain() public static void premain(string agentargs, Instrumentation inst) Provides opportunity to modify classes before loading Instrumentation class has useful methods

30 30 MANIFEST.MF Premain-Class: com.s.logging.loggingagent Boot-Class-Path: byte-buddy jar

31 31 Demo 2 Create a simple Java Agent

32 32 Another Example Add outputting logs before executing a particular method on a particular class

33 33 Example 1. Manipulate bytecode before loading Use premain() 2. Replace the class file Use ByteBuddy Not create a subclass

34 34 Target Class public class Target { public void foo() { System.out.println("foo!"); } public static void main(string[] args) { new Target().foo(); } }

35 35 Replace the class TypePool pool = TypePool.Default.ofClassPath(); return new ByteBuddy().rebase(pool.describe("c.Target").resolve(), ClassFileLocator.ForClassLoader.ofClassPath() )

36 Replace the class return new ByteBuddy().rebase(...) Replace the original implementation with new one Save the original implementation under a different method name 36

37 37 Enhance Existing Method ByteBuddy#subclass() Override the method ByteBuddy#redefine() Replace the implementation ByteBuddy#rebase() Copy&Rename the method Replace the implementation

38 38 Replace the class TypePool pool = TypePool.Default.ofClassPath(); return new ByteBuddy().rebase(pool.describe("c.Target").resolve(), Can't use a class literal JVM loads class before changing the class Use the TypePool class and describe()

39 39 Replace the class.rebase(pool.describe(...).resolve(), ClassFileLocator.ForClassLoader.ofClassPath() ) Allow to locate a class file ofclasspath() - Scan the running application's class path

40 40 Intercept the method return new ByteBuddy()....method(ElementMatchers.named("foo")).intercept( ) MethodDelegation.to(LoggingInterceptor.class).andThen(SuperMethodCall.INSTANCE)

41 41 Delegation MethodDelegation.to() Specify a Class to delegate A best match method is used

42 42 Intercept the method return new ByteBuddy()....method(ElementMatchers.named("foo")).intercept( ) MethodDelegation.to(LoggingInterceptor.class).andThen(SuperMethodCall.INSTANCE)

43 43 Interceptor Class public static class LoggingInterceptor { public static void Method m) {...println("call " + m.getname()...); } }

44 44 Delegated Method Annotations for Reference to the method/constructor

45 45 Delegated Method Annotations for Parameter Dynamic/Super @SuperCall Callable/Runnable instance of the super's implementation of the method

46 46 premain() public static void premain(string args, Instrumentation inst) { inst.addtransformer( new ClassFileTransformer() public byte[] transform(...) {

47 47 transform() public byte[] transform(classloader loader, String classname, Class<?> classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) { } // Call ByteBuddy

48 48 transform() public byte[] transform(classloader loader, String classname, Class<?> classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) classname Class name to be loaded classfilebuffer Class file content

49 49 transform() public byte[] transform(classloader loader, String classname, Class<?> classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) Return the class file content

50 50 Demo 3 Add outputting logs before executing a method

51 51

52 52 Features in ByteBuddy Add fields/methods Manipulate stack Generate CONDY bytecode Constant Dynamic JEP 309 Simplify Java Agent with AgentBuilder lots of other features

53 53 Byte Buddy's AgentBuilder Simplify the Java Agent implementation

54 54 AgentBuilder new AgentBuilder.Default().type(ElementMatchers.named("com.sakatakoic hi.logging.target")).transform(new AgentBuilder.Transformer() {... }).installon(inst);

55 55 AgentBuilder 1. Use AgentBuilder instead of ByteBuddy class 2. Use AgentBuilder.Transformer instead of ClassFileTransformer 3. Call installon()

56 Transformer.transform(new AgentBuilder.Transformer() { public DynamicType.Builder<?> transform( DynamicType.Builder<?> builder, TypeDescription typedescription, ClassLoader classloader, JavaModule javamodule) { return builder.method(elementmatch...named("foo")).intercept(...); } }) 56

57 57 Without -javaagent -javaagent option can be removed Call ByteBuddyAgent.install() Call AgentBuilder#installOnByteBuddyAgent() instead of installon() Need to add byte-buddy-agent.jar

58 58 Without -javaagent ByteBuddyAgent.install(); new AgentBuilder.Default().type(ElementMatchers.named("com.sakatakoic hi.logging.target")).transform(new AgentBuilder.Transformer() {... }).installonbytebuddyagent();

59 59 Demo 4 Add outputting logs without -javaagent option

60 60 Wrap Up BM is fun and close to us! Many libraries are using Application Examples Hot Swap Advanced Dynamic Proxy

61 61 Q&A