GeeCON Prague 2014 - Having fun with Javassist

Transcript

1. ! Having fun with Javassist Anton Arhipov @antonarhipov, 24th October 2014
2. Hello! (Who’s that?) Anton Arhipov ZeroTurnaround XRebel JRebel @antonarhipov Prague, 24th October 2014 @antonarhipov
3. Why Javassist? @antonarhipov Prague, 24th October 2014 It enables both tools I’m deeply involved with
4. Why Javassist? @antonarhipov Prague, 24th October 2014 Java bytecode manipulation made easy!
5. Why Javassist? @antonarhipov Prague, 24th October 2014 Java bytecode manipulation made easy!
6. Why Javassist? @antonarhipov Prague, 24th October 2014 It is fun!
7. The Plan for This PrEseNtAtiOn @antonarhipov Prague, 24th October 2014 Use cases for bytecode manipulation Code examples with Javassist How to brew a Java agent speakerdeck.com/antonarhipov github.com/zeroturnaround/callspy
8. BYTECODE MANIPULATION @antonarhipov Prague, 24th October 2014
9. Bytecode manipulation @antonarhipov Prague, 24th October 2014 Code analysis: Find bugs in your application Examine code complexity Find classes by specific attributes / annotations
10. Bytecode manipulation @antonarhipov Prague, 24th October 2014 Code generation: Lazy load data from a database using proxies Add cross-cutting concerns to the code Generate classes from non-Java artefacts
11. @antonarhipov Prague, 24th October 2014 The main use case for Javassist: generate proxies Bytecode manipulation i.e. create a subclass at runtime that intercepts all method invocations java.lang.reflect.Proxy is not enough Hibernate proxies Spring AOP EJB proxies CDI proxies
12. Bytecode manipulation @antonarhipov Prague, 24th October 2014 Transforming classes without source code: Code profiling Code optimisation Some other crazy things…
13. Bytecode manipulation @antonarhipov Prague, 24th October 2014 … and of course, dynamically add logging to application Good news everyone! We’ll implement a logger today!
14. Logging @antonarhipov Prague, 24th October 2014 public void doSomething(){ stmt; stmt;
 stmt; stmt;
 stmt;
 }

15. Logging @antonarhipov Prague, 24th October 2014 public void doSomething(){ // no logging here stmt;
 stmt; stmt;
 stmt;
 }

16. Logging @antonarhipov Prague, 24th October 2014 public void doSomething(){ // no logging here // argh!!!
 stmt; stmt;
 stmt;
 }
 If only I could add more logging here…
17. Logging @antonarhipov Prague, 24th October 2014 Instrument all the bytecode!
18. Logging @antonarhipov Prague, 24th October 2014 … with Javassist!
19. JAVASSIST @antonarhipov Prague, 24th October 2014
20. Javassist @antonarhipov Prague, 24th October 2014 Bytecode manipulation made easy Source-level and bytecode-level API Uses vocabulary for a Java language On-the-fly compilation of the injected code www.javassist.org
21. @antonarhipov Prague, 24th October 2014
22. @antonarhipov Prague, 24th October 2014
23. Javassist @antonarhipov Prague, 24th October 2014 ClassPool CtClass CtMethod CtClass CtClass CtClass CtField CtConst CtMethod insertBefore instrument insertAfter
24. JAVA AGENTS @antonarhipov Prague, 24th October 2014
25. How would you make a tool? A tool should not force the user into a special programming model! @antonarhipov Prague, 24th October 2014
26. -javaagent:logger.jar @antonarhipov Prague, 24th October 2014 Java agent to the rescue!
27. @antonarhipov Prague, 24th October 2014
28. @antonarhipov Prague, 24th October 2014 import java.lang.instrument.ClassFileTransformer;! import java.lang.instrument.Instrumentation;! ! public class Agent {! ! public static void premain(String args, Instrumentation inst) {! inst.addTransformer(new ClassFileTransformer { … });! }! ! public static void agentmain(String args, Instrumentation inst) {! premain(args, inst);! }! }
29. @antonarhipov Prague, 24th October 2014 public static void premain(String args, Instrumentation inst) • java -javaagent:<jarfile>[=options] • META-INF/MANIFEST.MF is required
30. @antonarhipov Prague, 24th October 2014 public static void agentmain(String args, Instrumentation inst) • Executed when the agent attaches to the running JVM • META-INF/MANIFEST.MF is required • Requires support for loading agents in JVM • Allows adding the code to JVM post-factum
31. Manifest-Version: 1.0 Ant-Version: Apache Ant 1.8.1 Created-By: 1.7.0_15-b03 (Oracle Corporation) Premain-Class: com.zeroturnaround.javarebel.java5.AgentInstall Can-Redefine-Classes: true Boot-Class-Path: jrebel.jar Main-Class: com.zeroturnaround.javarebel.java4.Install Implementation-Title: JRebel Specification-Title: jrebel Specification-Version: 5.4.0 Implementation-Version: 201309021535 MANIFEST.MF @antonarhipov Prague, 24th October 2014
32. import com.sun.tools.attach.VirtualMachine;! ! //attach to target VM! VirtualMachine vm = VirtualMachine.attach("2177");! ! //get system properties in the target VM! Properties props = vm.getSystemProperties();! ! //load agent into the VM! vm.loadAgent("agent.jar", "arg1=x,arg2=y");! ! //detach from VM! vm.detach();! http://docs.oracle.com/javase/7/docs/jdk/api/attach/spec/com/sun/tools/attach/VirtualMachine.html @antonarhipov Prague, 24th October 2014
33. JVM JVM Process 1 Process 2 Agent -cp tools.jar @antonarhipov Prague, 24th October 2014
34. Instrumentation API @antonarhipov Prague, 24th October 2014
35. java.lang.instrument.Instrumentation void addTransformer(ClassFileTransformer transformer,! boolean canRetransform);! ! void appendToBootstrapClassLoaderSearch(JarFile jarfile);! void appendToSystemClassLoaderSearch(JarFile jarfile);! ! Class[] getAllLoadedClasses();! Class[] getInitiatedClasses(ClassLoader loader);! ! void redefineClasses(ClassDefinition... classes);! void retransformClasses(Class<?>... classes);! @antonarhipov Prague, 24th October 2014
36. java.lang.instrument.ClassFileTransformer byte[] transform(ClassLoader loader, ! String className,! Class<?> classBeingRedefined,! ProtectionDomain pd,! byte[] classfileBuffer);! @antonarhipov Prague, 24th October 2014
37. public class MyTransformer implements ClassFileTransformer {! public void byte[] transform(ClassLoader loader, ! String className,! Class<?> classBeingRedefined,! ProtectionDomain pd,! byte[] classfileBuffer){! ! ClassPool cp = ClassPool.getDefault();! CtClass ct = cp.makeClass(new! ByteArrayInputStream(classfileBuffer));! ! // transform the bytes as required, ! // for instance - with Javassist! ! return ct.toBytecode();! }! }!
38. ! Class loading Instrumentation
39. ! Class loading Instrumentation ClassFileTransformer ClassFileTransformer ClassFileTransformer
40. ! Class loading Javassist Instrumentation ClassFileTransformer ClassFileTransformer ClassFileTransformer ASM
42. JAVASSIST APPLICATIONS Anton Arhipov Prague, 24th October 2014
43. JRebel Anton Arhipov Prague, 24th October 2014 JRebel core Spring plugin Hibernate plugin EJB plugin
44. JRebel Anton Arhipov Prague, 24th October 2014 JRebel core Spring plugin Hibernate plugin EJB plugin Reloads classes
45. JRebel Anton Arhipov Prague, 24th October 2014 JRebel core Spring plugin Hibernate plugin EJB plugin Notifies plugins
46. JRebel Anton Arhipov Prague, 24th October 2014 JRebel core Spring plugin Hibernate plugin EJB plugin Reload configurations
47. JRebel Anton Arhipov Prague, 24th October 2014 JRebel core Spring plugin Hibernate plugin EJB plugin Implemented with Javassist
48. Anton Arhipov Prague, 24th October 2014
49. XRebel Anton Arhipov Prague, 24th October 2014
50. XRebel Anton Arhipov Prague, 24th October 2014
51. XRebel Anton Arhipov Prague, 24th October 2014 Injected via the application server with Javassist
52. XRebel Anton Arhipov Prague, 24th October 2014
53. THANK YOU! Anton Arhipov Prague, 24th October 2014 anton@zeroturnaround.com @antonarhipov