Con-FESS 2015 - Having Fun With Javassist

Transcript

1. Having fun with Javassist Anton Arhipov
2. @antonarhipov Anton Arhipov
3. Why Javassist? Prototyping Simple integrations All framework integrations Workarounds / h4cKs
4. Why Javassist? Bytecode manipulation
5. Why Javassist? Bytecode manipulation made easy!
6. Agenda The use cases for bytecode manipulation Code examples with Javassist How to create your own Java agent speakerdeck.com/antonarhipov github.com/zeroturnaround/callspy
7. Bytecode manipulation Code analysis: Find bugs in your application Examine code complexity Find classes by specific attributes / annotations
8. Bytecode manipulation Code generation: Lazily load data using proxies Add cross-cutting concerns to the code Generate classes from non-Java artefacts
9. Bytecode manipulation Main use case for Javassist: generate proxies i.e. at runtime, create a subclass that intercepts all method invocations Spring AOP Hibernate proxies EJB proxies CDI proxies java.lang.reflect.Proxy is not enough
10. Bytecode manipulation Transform classes without source code Code profiling Code optimization Some other crazy things
11. Good news, everyone! We will implement a logger today!
12. public void doSomething(){ stmt; stmt;
 stmt; stmt;
 stmt;
 }

13. public void doSomething(){ // no logging here stmt;
 stmt; stmt;
 stmt;
 }

14. public void doSomething(){ // no logging here // argh!!!
 stmt; stmt;
 stmt;
 }
 If only I could add more logging here…
15. Instrument all the bytecode!
16. … with Javassist!
17. Javassist Bytecode manipulation made easy Source level and bytecode level APIs Uses vocabulary of a Java language On-the-fly compilation of injected code www.javassist.org
19. CtPool CtClass CtClass CtClass CtClass CtField CtMethod CtConst CtMethod insertBefore insertAfter instrument Javassist
20. -javaagent
22. 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); } }
23. public static void premain(String args, Instrumentation inst) java -javaagent:<jarfile>[=options] META-INF/MANIFEST.MF is required
24. 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
25. 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
26. 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
27. JVM JVM Process 1 Process 2 Agent -cp tools.jar
28. Instrumentation API
29. Instrumentation API 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);
30. byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain pd, byte[] classfileBuffer); ClassFileTransformer
31. public class MyTransformer implements ClassFileTransformer { public void byte[] transform(ClassLoader loader, String className, Class<?> toRefine, 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(); } }
32. Class loading Instrumentation
33. Class loading Instrumentation ClassFileTransformer ClassFileTransformer ClassFileTransformer
34. Class loading Instrumentation ClassFileTransformer ClassFileTransformer ClassFileTransformer Javassist ASM
36. JRebel core Spring plugin Hibernate plugin EJB plugin
37. JRebel core Spring plugin Hibernate plugin EJB plugin Reloads classes
38. JRebel core Spring plugin Hibernate plugin EJB plugin Notifies plugins
39. JRebel core Spring plugin Hibernate plugin EJB plugin Reload configurations
40. JRebel core Spring plugin Hibernate plugin EJB plugin Implemented with Javassist