import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
public class DynamicProxyExample {
public static void main(String[] args) {
byte[] classData = generateProxyClassData(MyInterface.class);
MyInterface proxy = ProxyGenerator.createProxy(classData);
proxy.sayHello();
}
private static byte[] generateProxyClassData(Class interfaze) {
String className = interfaze.getSimpleName() + "Proxy";
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, className, null, "java/lang/Object",
new String[]{interfaze.getName()});
MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
mv.visitCode();
mv.visitVarInsn(Opcodes.ALOAD, 0);
mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
mv.visitInsn(Opcodes.RETURN);
mv.visitMaxs(1, 1);
mv.visitEnd();
mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "sayHello", "()V", null, null);
mv.visitCode();
mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
mv.visitLdcInsn("Hello World!");
mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
mv.visitInsn(Opcodes.RETURN);
mv.visitMaxs(2, 1);
mv.visitEnd();
cw.visitEnd();
return cw.toByteArray();
}
}
class ProxyGenerator extends ClassLoader {
public static MyInterface createProxy(byte[] classData) {
ProxyGenerator classLoader = new ProxyGenerator();
Class proxyClass = classLoader.defineClass(null, classData, 0, classData.length);
try {
return (MyInterface) proxyClass.newInstance();
e.printStackTrace();
}
return null;
}
}
interface MyInterface {
void sayHello();
}
