От HotSwap до Java-агентов

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От HotSwap до Java-агентов горячая замена классов Специально для JUG.ru, 25 февраля 2017 @antonarhipov

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JRebel потому что…

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https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 2 3 4 5 6 7 8 10+

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https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 2 3 4 5 6 7 8 10+ Эффективные разработчики!

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https://zeroturnaround.com/rebellabs/java-ee-productivity-report-2011/ 10% 20% 30% 0.5 1 2 3 4 5 6 7 8 10+ Просиживают штаны??

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HotSwap Загрузщики классов Java-агенты и инструментация Проблемы

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hotswap EST. 2001

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instanceKlass constantPoolOop constants() constantPoolCacheOop cache() pool_holder() klassVTable Embedded klassITable Embedded Embedded statics nmethod code() method() constants() objArrayOop methodOop methods() M. Dmitriev. Safe class and data evolution in large and long-lived Java (тм) applications. Technical report, Mountain View. 2001

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А что если… hotswap++

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Dynamic Code Evolution for Java T. Würthinger, C. Wimmer, L. Stadler. 2010 Тело метода Методы Поля Иерархия + + + x x x Бинарно совместимые изменения Бинарно несовместимые изменения

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Dynamic Code Evolution for Java T. Würthinger, C. Wimmer, L. Stadler. 2010 A B C A’ B’ C’ Redeﬁne A, C

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A B C A’ B’ C’ Object

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“демо”? кто то сказал

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STATE This is all about…

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Classloaders

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Class> uc1 = User.class; Class> uc2 = new DynamicClassLoader().load("com.zt.User"); out.println(uc1.getName()); // com.zt.User out.println(uc2.getName()); // com.zt.User out.println(uc1.getClassLoader()); // sun.misc.Launcher$AppClassLoader@18b4aac2 out.println(uc2.getClassLoader()); // com.zt.DynamicClassLoader@22b4bba7 User.age = 11; out.println((int) ReflectUtil.getStaticFieldValue("age", uc1)); // 11 out.println((int) ReflectUtil.getStaticFieldValue("age", uc2)); // 10 public class User { public static int age = 10; }

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while(true) { Class> uc = new DynamicClassLoader().load("com.zt.User"); ReflectUtil.invokeStatic("getHobby", uc); } public class User { public Hobby getHobby() { return Basketball(); } }

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while(true) { Class> uc = new DynamicClassLoader().load("com.zt.User"); ReflectUtil.invokeStatic("getHobby", uc); } public class User { public Hobby getHobby() { return Basketball(); } }

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public static class Context { public HobbyService hobbyService = new HobbyService(); public void init() { hobbyService.user = new User(); } }

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public static class Context { public HobbyService hobbyService = new HobbyService(); public AnyService anyService = new AnyService(); public void init() { hobbyService.user = new User(); anyService.initialize() } } while(true) { Class> c = new DynamicClassLoader().load("com.zt.Context"); Object context = c.newInstance(); ReflectUtil.invokeMethod("init", context); invokeService(context); }

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DynamicClassLoader Context class HobbyService class User class Context object HobbyService object User object Перегружаемое пространство Живой поток

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org.springframework.boot spring-boot-devtools runtime DEMO

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

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ClassFileTransformer ClassA ClassA ClassA0 +field1 +field2 +field3 +method1 +method2 +method3 +method1 +method2 +method3 +field1 +field2 +field3 +proxy_methods A thousand years of productivity: the JRebel story E. Kabanov, V. Vene, 2012

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public class C extends X { int y = 5; int method1(int x) { return x + y; } void method2(String s) { System.out.println(s); } }

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public class C extends X { int y = 5; int method1(int x) { Object[] o = new Object[1]; o[0] = x; return Runtime.redirect(this, o, "C", "method1", "(I)I"); } void method2(String s) { Object[] o = new Object[1]; o[0] = s; return Runtime.redirect( this, o, "C", "method2", "(Ljava/lang/String;)V"); } }

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public abstract class C0 { public static int method1(C c, int x) { int tmp1 = Runtime.getFieldValue(c, "C", "y", "I"); return x + tmp1; } public static void method2(C c, String s) { PrintStream tmp1 = Runtime.getFieldValue( null, "java/lang/System", "out", "Ljava/io/PrintStream;"); Object[] o = new Object[1]; o[0] = s; Runtime.redirect( tmp1, o, "java/io/PrintStream;", "println", "(Ljava/lang/String;)V"); } } int method1(int x) { return x + y; }

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public class C extends X { int y = 5; int method1(int x) { return x + y; } //... } public class C extends X { int y = 5; int z() { return 10; } int method1(int x) { return x + y + z(); } //... }

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public class C1 { public static int z(C c) { return 10; } public static int method1(C c, int x) { int tmp1 = Runtime.getFieldValue(c, "C", "y", "I"); int tmp2 = Runtime.redirect(c, null, "C", "z", "(V)I"); return x + tmp1 + tmp2; } //... }

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DEMO

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anton@zeroturnaround.com @antonarhipov