GeeCON Prague 2014 - Having fun with Javassist

Transcript

1. !
   Having fun with
   Javassist
   Anton Arhipov
   @antonarhipov, 24th October 2014
   

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2. Hello! (Who’s that?)
   Anton Arhipov
   ZeroTurnaround
   XRebel
   JRebel
   @antonarhipov Prague, 24th October 2014
   @antonarhipov
   

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3. Why Javassist?
   @antonarhipov Prague, 24th October 2014
   It enables both tools I’m deeply involved with
   

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4. Why Javassist?
   @antonarhipov Prague, 24th October 2014
   Java bytecode manipulation made easy!
   

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5. Why Javassist?
   @antonarhipov Prague, 24th October 2014
   Java bytecode manipulation made easy!
   

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6. Why Javassist?
   @antonarhipov Prague, 24th October 2014
   It is fun!
   

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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
   

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8. BYTECODE MANIPULATION
   @antonarhipov Prague, 24th October 2014
   

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9. Bytecode manipulation
   @antonarhipov Prague, 24th October 2014
   Code analysis:
   Find bugs in your application
   Examine code complexity
   Find classes by specific attributes / annotations
   

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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
    

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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
    

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12. Bytecode manipulation
    @antonarhipov Prague, 24th October 2014
    Transforming classes without source code:
    Code profiling
    Code optimisation
    Some other crazy things…
    

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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!
    

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14. Logging
    @antonarhipov Prague, 24th October 2014
    public void doSomething(){
    stmt;
    stmt;

    stmt;
    stmt;

    stmt;

    }

    

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

    stmt;
    stmt;

    stmt;

    }

    

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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…
    

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17. Logging
    @antonarhipov Prague, 24th October 2014
    Instrument
    all the bytecode!
    

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18. Logging
    @antonarhipov Prague, 24th October 2014
    … with Javassist!
    

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19. JAVASSIST
    @antonarhipov Prague, 24th October 2014
    

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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
    

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21. @antonarhipov Prague, 24th October 2014
    

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22. @antonarhipov Prague, 24th October 2014
    

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23. Javassist
    @antonarhipov Prague, 24th October 2014
    ClassPool CtClass CtMethod
    CtClass
    CtClass
    CtClass
    CtField
    CtConst
    CtMethod
    insertBefore
    instrument
    insertAfter
    

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24. JAVA AGENTS
    @antonarhipov Prague, 24th October 2014
    

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25. How would you make a tool?
    A tool should not force the user
    into a special programming model!
    @antonarhipov Prague, 24th October 2014
    

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26. -javaagent:logger.jar
    @antonarhipov Prague, 24th October 2014
    Java agent to the rescue!
    

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27. @antonarhipov Prague, 24th October 2014
    

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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);!
    }!
    }
    

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29. @antonarhipov Prague, 24th October 2014
    public static void premain(String args, Instrumentation inst)
    • java -javaagent:[=options]
    
    • META-INF/MANIFEST.MF is required
    

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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
    

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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
    

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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
    

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33. JVM JVM
    Process 1 Process 2
    Agent
    -cp tools.jar
    @antonarhipov Prague, 24th October 2014
    

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34. Instrumentation API
    @antonarhipov Prague, 24th October 2014
    

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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
    

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36. java.lang.instrument.ClassFileTransformer
    byte[] transform(ClassLoader loader, !
    String className,!
    Class> classBeingRedefined,!
    ProtectionDomain pd,!
    byte[] classfileBuffer);!
    @antonarhipov Prague, 24th October 2014
    

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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();!
    }!
    }!
    

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38. !
    Class loading
    Instrumentation
    

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39. !
    Class loading
    Instrumentation ClassFileTransformer
    ClassFileTransformer
    ClassFileTransformer
    

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40. !
    Class loading
    Javassist
    Instrumentation ClassFileTransformer
    ClassFileTransformer
    ClassFileTransformer
    ASM
    

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42. JAVASSIST APPLICATIONS
    Anton Arhipov Prague, 24th October 2014
    

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43. JRebel
    Anton Arhipov Prague, 24th October 2014
    JRebel
    core
    Spring
    plugin
    Hibernate
    plugin
    EJB
    plugin
    

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44. JRebel
    Anton Arhipov Prague, 24th October 2014
    JRebel
    core
    Spring
    plugin
    Hibernate
    plugin
    EJB
    plugin
    Reloads
    classes
    

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45. JRebel
    Anton Arhipov Prague, 24th October 2014
    JRebel
    core
    Spring
    plugin
    Hibernate
    plugin
    EJB
    plugin
    Notifies
    plugins
    

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46. JRebel
    Anton Arhipov Prague, 24th October 2014
    JRebel
    core
    Spring
    plugin
    Hibernate
    plugin
    EJB
    plugin
    Reload
    configurations
    

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47. JRebel
    Anton Arhipov Prague, 24th October 2014
    JRebel
    core
    Spring
    plugin
    Hibernate
    plugin
    EJB
    plugin
    Implemented with Javassist
    

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48. Anton Arhipov Prague, 24th October 2014
    

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49. XRebel
    Anton Arhipov Prague, 24th October 2014
    

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50. XRebel
    Anton Arhipov Prague, 24th October 2014
    

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51. XRebel
    Anton Arhipov Prague, 24th October 2014
    Injected via the application server with Javassist
    

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52. XRebel
    Anton Arhipov Prague, 24th October 2014
    

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53. THANK YOU!
    Anton Arhipov Prague, 24th October 2014
    anton@zeroturnaround.com
    @antonarhipov
    

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