Custom Class Loader in Java

Question

Is it possible to create your own custom class loader in java. If so, please guide me. Instead of the obfuscation class, I want to change the class file so that it cannot be canceled by any tool

Answer 1

You can use some obfuscation tools such as ProGuard.

The self-written ClassLoader must be placed in a standard .class file that the JVM can load. And then you can protect the truck from reverse engineering.

Do not do it yourself. Writing "safe" code without knowing cryptographic algorithms will lead to an erroneous presentation of unsafe code

Answer 2

import java.io.BufferedInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.HashMap; import java.util.Map; /** * * Simple custom class loader implementation * */ public class CustomClassLoader extends ClassLoader { /** * The HashMap where the classes will be cached */ private Map<String, Class<?>> classes = new HashMap<String, Class<?>>(); @Override public String toString() { return CustomClassLoader.class.getName(); } @Override protected Class<?> findClass(String name) throws ClassNotFoundException { if (classes.containsKey(name)) { return classes.get(name); } byte[] classData; try { classData = loadClassData(name); } catch (IOException e) { throw new ClassNotFoundException("Class [" + name + "] could not be found", e); } Class<?> c = defineClass(name, classData, 0, classData.length); resolveClass(c); classes.put(name, c); return c; } /** * Load the class file into byte array * * @param name * The name of the class eg com.codeslices.test.TestClass} * @return The class file as byte array * @throws IOException */ private byte[] loadClassData(String name) throws IOException { BufferedInputStream in = new BufferedInputStream( ClassLoader.getSystemResourceAsStream(name.replace(".", "/") + ".class")); ByteArrayOutputStream out = new ByteArrayOutputStream(); int i; while ((i = in.read()) != -1) { out.write(i); } in.close(); byte[] classData = out.toByteArray(); out.close(); return classData; } /** * Simple usage of the CustomClassLoader implementation * * @param args * @throws ClassNotFoundException * @throws IllegalAccessException * @throws InstantiationException * @throws SecurityException * @throws NoSuchMethodException * @throws InvocationTargetException * @throws IllegalArgumentException */ public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException { CustomClassLoader loader = new CustomClassLoader(); // This class should be in your application class path Class<?> c = loader.findClass("net.codeslices.test.TestClass"); Object o = c.newInstance(); Method m = c.getMethod("toString"); System.out.println(m.invoke(o)); } }