Java agents are watching your ByteCode
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The document discusses the creation and use of Java agents for bytecode manipulation, detailing various methods and tools related to class loading instrumentation. It includes examples of implementing class file transformers and provides code snippets for different functionalities, such as calculating object sizes and tracing method calls. Additionally, contact information for support is provided at the end.
![import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;
public class Agent {
public static premain(String args, Instrumentation instr) throws Exception {
instr.addTransformer(new ClassFileTransformer() {
///////////////////
});
}
}
META-INF/MANIFEST.MF
Premain-Class: Agent
https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html
-javaagent:jarpath[=options]](https://image.slidesharecdn.com/javaagents-170616092257/85/Java-agents-are-watching-your-ByteCode-9-320.jpg)
![new ClassFileTransformer() {
@Override
public byte[] transform(ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer)
throws IllegalClassFormatException {
ClassPool cp = ClassPool.getDefault();
CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer));
// ct transformation
return ct.toByteCode();
}
}](https://image.slidesharecdn.com/javaagents-170616092257/85/Java-agents-are-watching-your-ByteCode-10-320.jpg)
![public class ClassTransformer implements ClassFileTransformer {
public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer)
throws IllegalClassFormatException {
if(className.startsWith("tt")) return null;
try {
ClassPool pool = ClassPool.getDefault();
CtClass s1 = pool.get("java.lang.System");
CtMethod m11 = s1.getDeclaredMethod("currentTimeMillis");
CtClass s2 = pool.get("tt.MySystem");
CtMethod m21 = s2.getDeclaredMethod("currentTimeMillis");
CodeConverter cc = new CodeConverter();
cc.redirectMethodCall(m11, m21);
CtClass cl = pool.makeClass(new ByteArrayInputStream(classfileBuffer), false);
if(cl.isFrozen()) return null;
CtConstructor[] constructors = cl.getConstructors();
for(CtConstructor constructor : constructors) {
constructor.instrument(cc);
}
CtMethod[] methods = cl.getDeclaredMethods();
for(CtMethod method : methods) {
method.instrument(cc);
}
classfileBuffer = cl.toBytecode();
} catch (Exception ex) {
System.out.println("Exception: " + ex);
ex.printStackTrace();
}
return classfileBuffer;
}
}
public class MySystem {
public static long currentTimeMillis() {
return 1234567890L;
}
}
public class TimeMachine {
public static void main(String[] args) {
System.out.println(System.currentTimeMillis());
}
}](https://image.slidesharecdn.com/javaagents-170616092257/85/Java-agents-are-watching-your-ByteCode-11-320.jpg)
![public class TraceTransformer implements ClassFileTransformer {
private static StringBuilder space = new StringBuilder(" |___");
@Override
public byte[] transform(ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer) {
try {
if (!className.startsWith("jav/smart")) {
return classfileBuffer;
}
ClassPool cp = ClassPool.getDefault();
CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer));
CtMethod[] methods = ct.getDeclaredMethods();
for (CtMethod method : methods) {
space.insert(0, " ");
String methodBody = "{System.out.println(""+ space.toString() + className + "." + method.getName() +" ");}";
method.insertBefore(methodBody);
}
return ct.toBytecode();
} catch (Exception e) {
e.printStackTrace();
}
return classfileBuffer;
}
}](https://image.slidesharecdn.com/javaagents-170616092257/85/Java-agents-are-watching-your-ByteCode-12-320.jpg)
![public class ClassTransformer implements ClassFileTransformer {
private static int count = 0;
@Override
public byte[] transform(ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer) {
System.out.println(String.format("%d. Loading class: %s ",++count, className.replaceAll("/", ".")));
return classfileBuffer;
}
}](https://image.slidesharecdn.com/javaagents-170616092257/85/Java-agents-are-watching-your-ByteCode-13-320.jpg)
Java agents are watching your ByteCode
- 1. Agents are watching your bytecode. Roman Tsypuk
- 2. Agenda • WebGoat • Xrebel • Javasist (basics, demo method timing calculation) • How to create and pack your own JavaAgent • Demo create Agents (agent calculates loaded classes) • (agent shows obj size) • (agent traces the methods call chain) • (agent time machine)
- 5. Software Engineering Economics by Barry Boehm
- 9. import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static premain(String args, Instrumentation instr) throws Exception { instr.addTransformer(new ClassFileTransformer() { /////////////////// }); } } META-INF/MANIFEST.MF Premain-Class: Agent https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html -javaagent:jarpath[=options]
- 10. new ClassFileTransformer() { @Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); // ct transformation return ct.toByteCode(); } }
- 11. public class ClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { if(className.startsWith("tt")) return null; try { ClassPool pool = ClassPool.getDefault(); CtClass s1 = pool.get("java.lang.System"); CtMethod m11 = s1.getDeclaredMethod("currentTimeMillis"); CtClass s2 = pool.get("tt.MySystem"); CtMethod m21 = s2.getDeclaredMethod("currentTimeMillis"); CodeConverter cc = new CodeConverter(); cc.redirectMethodCall(m11, m21); CtClass cl = pool.makeClass(new ByteArrayInputStream(classfileBuffer), false); if(cl.isFrozen()) return null; CtConstructor[] constructors = cl.getConstructors(); for(CtConstructor constructor : constructors) { constructor.instrument(cc); } CtMethod[] methods = cl.getDeclaredMethods(); for(CtMethod method : methods) { method.instrument(cc); } classfileBuffer = cl.toBytecode(); } catch (Exception ex) { System.out.println("Exception: " + ex); ex.printStackTrace(); } return classfileBuffer; } } public class MySystem { public static long currentTimeMillis() { return 1234567890L; } } public class TimeMachine { public static void main(String[] args) { System.out.println(System.currentTimeMillis()); } }
- 12. public class TraceTransformer implements ClassFileTransformer { private static StringBuilder space = new StringBuilder(" |___"); @Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) { try { if (!className.startsWith("jav/smart")) { return classfileBuffer; } ClassPool cp = ClassPool.getDefault(); CtClass ct = cp.makeClass(new ByteArrayInputStream(classfileBuffer)); CtMethod[] methods = ct.getDeclaredMethods(); for (CtMethod method : methods) { space.insert(0, " "); String methodBody = "{System.out.println(""+ space.toString() + className + "." + method.getName() +" ");}"; method.insertBefore(methodBody); } return ct.toBytecode(); } catch (Exception e) { e.printStackTrace(); } return classfileBuffer; } }
- 13. public class ClassTransformer implements ClassFileTransformer { private static int count = 0; @Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) { System.out.println(String.format("%d. Loading class: %s ",++count, className.replaceAll("/", "."))); return classfileBuffer; } }
- 14. Questions?
- 15. USA HQ Toll Free: 866-687-3588 Tel: +1-512-516-8880 Ukraine HQ Tel: +380-32-240-9090 Bulgaria Tel: +359-2-902-3760 Thank you!