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package labs;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.stream.Collectors;
import jdk.internal.org.objectweb.asm.ClassWriter;
import jdk.internal.org.objectweb.asm.MethodVisitor;
import jdk.internal.org.objectweb.asm.Opcodes;
import jdk.internal.org.objectweb.asm.Type;
/**
* @author Thomas Darimont
*/
public class DefaultMethodProxyExample {
public static void main(String[] args) throws Throwable {
MessageHandler staticHandler = createInstanceViaAnonymousInnerClass();
staticHandler.handle(new Message());
MessageHandler dynamicProxyHandler = createDynamicInstanceViaDynamicProxy();
dynamicProxyHandler.handle(new Message());
MessageHandler dynamicGeneratedHandler = createDynamicInstanceViaGeneratedClass();
dynamicGeneratedHandler.handle(new Message());
}
private static MessageHandler createDynamicInstanceViaDynamicProxy() {
ClassLoader cl = Thread.currentThread().getContextClassLoader();
Class<?>[] ifaces = new Class[] { MessageHandler.class };
InvocationHandler ivocationHandler = (Object proxy, Method method, Object[] arguments) -> //
MethodHandles.lookup() //
.in(method.getDeclaringClass()) //
.unreflectSpecial(method, method.getDeclaringClass()) //
.bindTo(proxy) //
.invokeWithArguments(arguments);
return (MessageHandler) Proxy.newProxyInstance(cl, ifaces, ivocationHandler);
}
private static MessageHandler createDynamicInstanceViaGeneratedClass() {
return ProxyFactory.INSTANCE.newProxyInstance(MessageHandler.class);
}
private static MessageHandler createInstanceViaAnonymousInnerClass() {
return new MessageHandler() {};
}
static class Message {}
public static interface MessageHandler {
default void handle(Message message) {
System.out.println("Demo: " + this.getClass());
System.out.printf("Handle: %s%n", message);
System.out.printf("Callstack: %n%s%n %n", //
Arrays.asList(Thread.currentThread().getStackTrace()).stream() //
.map(Object::toString).collect(Collectors.joining("\n")) //
);
}
}
static enum ProxyFactory {
INSTANCE;
public <T> T newProxyInstance(Class<T> iface) {
Class<T> proxyClass = ProxyClassGenerator.INSTANCE.generateClass(iface);
try {
return iface.cast(proxyClass.newInstance());
} catch (InstantiationException | IllegalAccessException e) {
throw new RuntimeException(e);
}
}
}
static enum ProxyClassGenerator implements Opcodes {
INSTANCE;
private static final String PROXY_SUFFIX = "_Proxy";
private static final ConcurrentMap<Class<?>, Class<?>> PROXY_CLASS_CACHE = new ConcurrentHashMap<>();
private Class<?> generateProxyClass(Class<?> iface) {
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
String ifaceTypeName = Type.getInternalName(iface);
String proxyClassName = ifaceTypeName + PROXY_SUFFIX;
// class definition
cw.visit(V1_8, ACC_PUBLIC + ACC_SUPER, proxyClassName, null, "java/lang/Object", new String[] { ifaceTypeName });
// default constructor
MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
mv.visitInsn(RETURN);
mv.visitMaxs(0, 0);
mv.visitEnd();
return ByteArrayClassLoader.INSTANCE.loadClass(iface.getName() + PROXY_SUFFIX, cw.toByteArray());
}
@SuppressWarnings("unchecked")
public <T> Class<T> generateClass(Class<T> iface) {
return (Class<T>) PROXY_CLASS_CACHE.computeIfAbsent(iface, this::generateProxyClass);
}
}
static class ByteArrayClassLoader extends ClassLoader {
public static final ByteArrayClassLoader INSTANCE = new ByteArrayClassLoader();
private ByteArrayClassLoader() {}
public Class<?> loadClass(String name, byte[] bytes) {
Class<?> clazz = findLoadedClass(name);
return clazz != null ? clazz : defineClass(name, bytes, 0, bytes.length);
}
}
}
Demo: class labs.DefaultMethodProxyExample$1
Handle: labs.DefaultMethodProxyExample$Message@3b07d329
Callstack:
java.lang.Thread.getStackTrace(Thread.java:1552)
labs.DefaultMethodProxyExample$MessageHandler.handle(DefaultMethodProxyExample.java:66)
labs.DefaultMethodProxyExample.main(DefaultMethodProxyExample.java:25)
Demo: class com.sun.proxy.$Proxy0
Handle: labs.DefaultMethodProxyExample$Message@70177ecd
Callstack:
java.lang.Thread.getStackTrace(Thread.java:1552)
labs.DefaultMethodProxyExample$MessageHandler.handle(DefaultMethodProxyExample.java:66)
java.lang.invoke.LambdaForm.interpret_L(LambdaForm.java:664)
java.lang.invoke.LambdaForm.interpret_L(LambdaForm.java:664)
java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:625)
labs.DefaultMethodProxyExample.lambda$0(DefaultMethodProxyExample.java:44)
labs.DefaultMethodProxyExample$$Lambda$6/1922154895.invoke(Unknown Source)
com.sun.proxy.$Proxy0.handle(Unknown Source)
labs.DefaultMethodProxyExample.main(DefaultMethodProxyExample.java:28)
Demo: class labs.DefaultMethodProxyExample$MessageHandler_Proxy
Handle: labs.DefaultMethodProxyExample$Message@6f539caf
Callstack:
java.lang.Thread.getStackTrace(Thread.java:1552)
labs.DefaultMethodProxyExample$MessageHandler.handle(DefaultMethodProxyExample.java:66)
labs.DefaultMethodProxyExample.main(DefaultMethodProxyExample.java:31)
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