how and why to instrument Java classes

1. Как и зачем инструментировать
байткод в Java приложениях?
Специально для JUG.ua, 25 мая 2017
@antonarhipov

2. Антон Архипов
@antonarhipov
Javassist & ASM inside!
Привет!

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;

8. Зачем?
Модели программирования (AOP, ORM, итд)
Специализированные отладчики
Агенты для мониторинга (NewRelic, XRebel)
Инструменты для разработки (JRebel)
Обфускация (Proguard)
итд

9. Починить
ошибку в
open-source
библиотеке.
Потому, что я
могу!

10. Как?
java.lang.instrument
-javaagent
ASM, Javassist, Byte Buddy, cglib, итд
Classloaders

11. ASM

12. public class Hello {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}

13. public class Hello {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
> javap -c Hello
Дизассемблировать Hello

14. public class Hello {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
> javap -c Hello
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

16. java -cp asm-all-3.3.1.jar:asm-util-3.3.1.jar
org.objectweb.asm.util.ASMifierClassVisitor
Items.class

17. ASM
“Сделаю всё как хочу”
Приходится писать много кода
Надо понимать Java-байткод

18. byte
buddy

19. Class<?> dynamicType = new ByteBuddy()
.subclass(Object.class)
.method(ElementMatchers.named("toString"))
.intercept(FixedValue.value("Hello World!"))
.make()
.load(getClass().getClassLoader())
.getLoaded();
System.out.println(dynamicType.newInstance().toString()); //Hello World!
System.out.println(dynamicType);
//class net.bytebuddy.renamed.java.lang.Object$ByteBuddy$KUZX06bM

20. Byte Buddy
Модный API
Попурялный / активный проект
“Много магии”

21. JAVASSIST

22. API
ClassPool
CtClass
CtClass
CtClass
CtClass
CtField
CtMethod
CtConst
CtMethod
insertBefore
insertAfter
instrument

23. 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");
}

24. 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();

25. 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() {
}
}

26. 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");
}

27. 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

28. 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");
}

29. 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");
}

30. 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");
}

31. 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() {
}

32. 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) {
}

33. 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");
}
Дескрипторы бывают длинноваты ;)

34. 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 — локальные переменные
$0 — this (для виртуальных методов)

35. 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)

36. 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");
}

37. CtMethod foo = …
foo.insertBefore(…);
foo.insertAfter(…);
Можно реализовать
трассировку
… или добавить логирование
… или реализовать свой “AOP”

38. CtMethod foo = …
foo.instrument(new ExprEditor() {
@Override
public void edit(NewExpr e)
throws CannotCompileException {
e.replace("{" +
"$_ = $proceed($$);" +
"System.out.println($_);" +
"}");
}
});

39. CtMethod foo = …
foo.instrument(new ExprEditor() {
@Override
public void edit(NewExpr e)
throws CannotCompileException {
e.replace("{" +
"$_ = $proceed($$);" +
"System.out.println($_);" +
"}");
}
});

40. CtMethod foo = …
foo.instrument(new ExprEditor() {
@Override
public void edit(NewExpr e)
throws CannotCompileException {
e.replace("{" +
"$_ = $proceed($$);" +
"System.out.println($_);" +
"}");
}
});

41. CtMethod foo = …
foo.instrument(new ExprEditor() {
@Override
public void edit(MethodCall m)
throws CannotCompileException {
if(m.getMethodName().contains("println")) {
m.replace("{}");
}
}
});

42. CtMethod foo = …
foo.instrument(new ExprEditor() {
@Override
public void edit(FieldAccess m)
throws CannotCompileException {
if (f.isWriter()) {
CtField field = f.getField();
String setterName = findSetter(field);
f.replace("{" + "$0." + setterName + "($$);" + "}");
}
}
});

43. Javassist
“Простой как тесак”
Неприхотлив в использовании
Производительность - так себе :(

44. Java-агенты

45. 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 dragons
});
}
}
$> java –javaagent:agent.jar application.Main
META-INF/MANIFEST.MF
Premain-Class: Agent

46. https://www.youtube.com/watch?v=SY5lMgWlHAw

47. DEMO
https://github.com/zeroturnaround/callspy
https://github.com/bsideup/javaagent-boilerplate

48. anton@zeroturnaround.com
@antonarhipov