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LordMZTE/InstrClass.java

Last active June 20, 2020 14:15
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Injecting Instrumented classes to classpath at runtime with javaassist
Raw
InstrClass.java
package de.mzte.test;
public class InstrClass {
public static void sayHello() {
System.out.println("Hello!");
}
}
Raw
Main.java
package de.mzte.test;
import javassist.*;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Main {
public static void main(String[] args) throws NotFoundException, CannotCompileException, IOException, IllegalAccessException, NoSuchMethodException, InvocationTargetException {
//Instrument class
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("de.mzte.test.InstrClass");
CtMethod m = cc.getDeclaredMethod("sayHello");
m.insertBefore("System.out.println(\"Someone Said Hello!\");");
cc.defrost();
cc.writeFile();
//Inject class into classpath
ClassLoader classLoader = ClassLoader.getSystemClassLoader();
Method method = ClassLoader.class.getDeclaredMethod("addClass", Class.class);
method.setAccessible(true);
method.invoke(classLoader, cc.toClass());
//Call Like normal
InstrClass.sayHello();
InstrClass.sayHello();
InstrClass.sayHello();
InstrClass.sayHello();
}
}
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