JEEConf 2017 - Having fun with Javassist

Transcript

1. Having fun with Javassist JEEConf 2017 @antonarhipov

2. whoami Anton Arhipov @antonarhipov Javassist inside!

3. None

4. @Entity
 @Table(name = "owners")
 public class Owner extends Person {


   @Column(name = "address")
 @NotEmpty
 private String address;
 
 @Column(name = "city")
 @NotEmpty
 private String city;
 
 @Column(name = "telephone")
 @NotEmpty
 @Digits(fraction = 0, integer = 10)
 private String telephone;
 
 @OneToMany(cascade = CascadeType.ALL, mappedBy = "owner")
 private Set<Pet> pets;

5. public class JavassistLazyInitializer extends BasicLazyInitializer implements MethodHandler { final JavassistLazyInitializer

   instance = new JavassistLazyInitializer(…); 
 ProxyFactory factory = new ProxyFactory();
 factory.setSuperclass(interfaces.length == 1?persistentClass:null);
 factory.setInterfaces(interfaces);
 factory.setFilter(FINALIZE_FILTER); 
 Class cl = factory.createClass();
 final HibernateProxy proxy = (HibernateProxy) cl.newInstance();
 ((ProxyObject)proxy).setHandler(instance);
 instance.constructed = true;
 return proxy;

6. public class JavassistLazyInitializer extends BasicLazyInitializer implements MethodHandler { final JavassistLazyInitializer

   instance = new JavassistLazyInitializer(…); 
 ProxyFactory factory = new ProxyFactory();
 factory.setSuperclass(interfaces.length == 1?persistentClass:null);
 factory.setInterfaces(interfaces);
 factory.setFilter(FINALIZE_FILTER); 
 Class cl = factory.createClass();
 final HibernateProxy proxy = (HibernateProxy) cl.newInstance();
 ((ProxyObject)proxy).setHandler(instance);
 instance.constructed = true;
 return proxy;

7. The main use case for bytecode generation in Java frameworks

   is to generate proxies
8. None

9. Why? Programming model (AOP, ORM, итд) Monitoring agent (NewRelic, XRebel)

   Specialized debuggers Developer tools (JRebel) Obfuscation (Proguard)

10. Javassist 101 www.javassist.org

11. API ClassPool CtClass CtClass CtClass CtClass CtField CtMethod CtConst CtMethod

    insertBefore insertAfter instrument

12. https://speakerdeck.com/antonarhipov

13. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); }

14. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); } ClassPool cp = new ClassPool(null); cp.appendSystemPath();

15. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); } public class A extends Clazz { 
 public A() {
 }
 }

16. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); }

17. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); } mars:output anton$ javap -c com/zt/A.class public class com.zt.A extends com.zt.Clazz { public com.zt.A(); Code: 0: aload_0 1: invokespecial #10 4: return

18. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ct = cp.makeClass("com.zt.A", cp.get("com.zt.Clazz")); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); } Can generate classes from metadata at build time

19. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); cp.appendClassPath(new ClassPath(){ … }); CtClass ct = cp.get("com.zt.A"); CtMethod[] methods = ct.getMethods();
 for (CtMethod method : methods) {
 //… } ct.writeFile("/output"); } … or you can post process the compiled classes

20. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "()V"); foo.insertBefore("System.out.println();"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 }

21. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "()V"); foo.insertBefore("System.out.println();"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 }

22. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "()V"); foo.insertBefore("System.out.println();"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 } public void foo() { 
 }

23. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "(Ljava/lang/String;)V"); foo.insertBefore("System.out.println();"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 } public void foo(String s) { 
 }

24. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lja foo.insertBefore("System.out.println();"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 } Descriptors might get quite long ;)

25. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "(Ljava/lang/String;)V"); foo.insertBefore("System.out.println($1)"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 } $1, $2, $3 — local variables $0 — this for non-static methods

26. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "(Ljava/lang/String;)V"); foo.insertBefore("System.out.println($1)"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 } Exception in thread "main" javassist.CannotCompileException: [source error] ; is missing at javassist.CtBehavior.insertBefore(CtBehavior.java:774) at javassist.CtBehavior.insertBefore(CtBehavior.java:734) at com.zt.basics.Ex.main(Ex.java:35)

27. public static void main(String[] args) throws Exception { ClassPool cp

    = ClassPool.getDefault(); CtClass ctClass = cp.get("com.zt.A"); CtMethod foo = ctClass.getMethod("foo", "(Ljava/lang/String;)V"); foo.insertBefore("System.out.println($1);"); Class c = ctClass.toClass();
 A a = (A) c.newInstance();
 a.foo("Hello");
 }

28. CtMethod foo = … foo.insertBefore(…); foo.insertAfter(…); Can implement tracing

29. … or add logging CtMethod foo = … foo.insertBefore(…); foo.insertAfter(…);

30. … or implement AOP CtMethod foo = … foo.insertBefore(…); foo.insertAfter(…);

31. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(NewExpr e) throws CannotCompileException {
 e.replace("{" +
 "$_ = $proceed($$);" +
 "System.out.println($_);" +
 "}");
 } });

32. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(NewExpr e) throws CannotCompileException {
 e.replace("{" +
 "$_ = $proceed($$);" +
 "System.out.println($_);" +
 "}");
 } });

33. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(NewExpr e) throws CannotCompileException {
 e.replace("{" +
 "$_ = $proceed($$);" +
 "System.out.println($_);" +
 "}");
 } }); Intercept new instances

34. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(NewExpr e) throws CannotCompileException {
 e.replace("{" +
 "$_ = $proceed($$);" +
 "System.out.println($_);" +
 "}");
 } }); Intercept new instances

35. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(MethodCall m) throws CannotCompileException {
 if(m.getMethodName().contains("println")) {
 m.replace("{}");
 } } }); Remove unwanted invocations

36. CtMethod foo = … foo.instrument(new ExprEditor() { @Override
 public void

    edit(FieldAccess f) throws CannotCompileException {
 if (f.isWriter()) {
 CtField field = f.getField();
 String setterName = findSetter(field);
 f.replace("{" + "$0." + setterName + "($$);" + "}");
 } } }); Replace direct field access with setter calls

37. java.lang.ClassFormatError: LVTT entry for 'callbackTypes' in class file com/google/inject/internal/ProxyFactory does

    not match any LVT entry

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39. Java agents

40. Java Agent import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent {

    public static void premain(String args, Instrumentation inst) throws Exception { inst.addTransformer(new ClassFileTransformer { // here be code }); } } META-INF/MANIFEST.MF Premain-Class: Agent $> java –javaagent:agent.jar application.Main

41. ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className,

    Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); // here we can do all the things to ‘ct’ return ct.toBytecode(); } }

42. new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>

    classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); // here we can do all the things to ‘ct’ return ct.toBytecode(); } } ClassFileTransformer

43. new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>

    classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); // here we can do all the things to ‘ct’ return ct.toBytecode(); } } ClassFileTransformer

44. new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>

    classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); // here we can do all the things to ‘ct’ return ct.toBytecode(); } } ClassFileTransformer
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50. https://github.com/zeroturnaround/callspy

51. Javassist in

52. JRebel core Spring plugin Hibernate plugin EJB plugin

53. JRebel core Spring plugin Hibernate plugin EJB plugin jrebel.jar

54. Reloads classes JRebel core Spring plugin Hibernate plugin EJB plugin

55. Notifies plugins JRebel core Spring plugin Hibernate plugin EJB plugin

56. JRebel core Spring plugin Hibernate plugin EJB plugin Refresh configurations

57. Javassist lives here Spring plugin Hibernate plugin EJB plugin JRebel

    core

58. Spring Hibernate OpenEJB JRebel core Spring plugin Hibernate plugin EJB

    plugin

59. class Framework { public void configure(){ //…
 } } CtClass

    framework = cp.get("com.zt.Framework"); framework.addInterface( cp.get("com.zt.jrebel.Listener")); class Framework implements Listener { public void configure(){
 } } framework.addMethod( CtNewMethod.make( "public void onEvent(){" + " configure();" + "}", framework ));

60. https://github.com/antonarhipov/jpoint HowItWorks

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62. Your task Javassist

63. https://speakerdeck.com/antonarhipov http://www.slideshare.net/arhan @antonarhipov [email protected]