Recommended
Recommended
More Related Content
What's hot
What's hot (20)
Similar to Con-FESS 2015 - Having Fun With Javassist
Similar to Con-FESS 2015 - Having Fun With Javassist (20)
More from Anton Arhipov
More from Anton Arhipov (20)
Recently uploaded
Recently uploaded (20)
Con-FESS 2015 - Having Fun With Javassist
- 1. Having fun with Javassist Anton Arhipov
- 3. Why Javassist? Prototyping Simple integrations All framework integrations Workarounds / h4cKs
- 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!
- 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…
- 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
- 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
- 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(); } }