用例是实现脏字段跟踪器。为此,我有一个界面:
public interface Dirtyable {
String ID = "dirty";
Set<String> getDirty();
static <T> T wrap(final T delegate) {
return DirtyableInterceptor.wrap(delegate, ReflectionUtils::getPropertyName);
}
static <T> T wrap(final T delegate, final Function<Method, String> resolver) {
return DirtyableInterceptor.wrap(delegate, resolver);
}
}
在拦截器类中,包装方法是:
static <T> T wrap(final T delegate, final Function<Method, String> resolver) {
requireNonNull(delegate, "Delegate must be non-null");
requireNonNull(resolver, "Resolver must be non-null");
final Try<Class<T>> delegateClassTry = Try.of(() -> getClassForType(delegate.getClass()));
return delegateClassTry.flatMapTry(delegateClass ->
dirtyableFor(delegate, delegateClass, resolver))
.mapTry(Class::newInstance)
.getOrElseThrow(t -> new IllegalStateException(
"Could not wrap dirtyable for " + delegate.getClass(), t));
}
该方法dirtyableFor
定义了一个 ByteBuddy,它在每次调用时转发到一个特定的实例。但是,在每次调用时进行检测有点昂贵,因此它会缓存来自给定实例类的检测子类。为此,我使用resilience4j
库(又名javaslang-circuitbreaker
)。
private static <T> Try<Class<? extends T>> dirtyableFor(final T delegate,
final Class<T> clazz,
final Function<Method, String> resolver) {
long start = System.currentTimeMillis();
Try<Class<? extends T>> r = Try.of(() -> ofCheckedSupplier(() ->
new ByteBuddy().subclass(clazz)
.defineField(Dirtyable.ID, Set.class, Visibility.PRIVATE)
.method(nameMatches("getDirty"))
.intercept(reference(new HashSet<>()))
.implement(Dirtyable.class)
.method(not(isDeclaredBy(Object.class))
.and(not(isAbstract()))
.and(isPublic()))
.intercept(withDefaultConfiguration()
.withBinders(Pipe.Binder.install(Function.class))
.to(new DirtyableInterceptor(delegate, resolver)))
.make().load(clazz.getClassLoader())
.getLoaded())
.withCache(getCache())
.decorate()
.apply(clazz));
System.out.println("Instrumentation time: " + (System.currentTimeMillis() - start));
return r;
}
private static <T> Cache<Class<? super T>, Class<T>> getCache() {
final CachingProvider provider = Caching.getCachingProvider();
final CacheManager manager = provider.getCacheManager();
final javax.cache.Cache<Class<? super T>, Class<T>> cache =
manager.getCache(Dirtyable.ID);
final Cache<Class<? super T>, Class<T>> dirtyCache = Cache.of(cache);
dirtyCache.getEventStream().map(Object::toString).subscribe(logger::debug);
return dirtyCache;
}
从日志中,检测时间从缓存未命中的 70-100 毫秒下降到缓存命中的 0-2 毫秒。
为了完整起见,这里是拦截器方法:
@RuntimeType
@SuppressWarnings("unused")
public Object intercept(final @Origin Method method, final @This Dirtyable dirtyable,
final @Pipe Function<Object, Object> pipe) throws Throwable {
if (ReflectionUtils.isSetter(method)) {
final String property = resolver.apply(method);
dirtyable.getDirty().add(property);
logger.debug("Intercepted setter [{}], resolved property " +
"[{}] flagged as dirty.", method, property);
}
return pipe.apply(this.delegate);
}
这个解决方案效果很好,除了DirtyableInterceptor
缓存命中总是相同的,所以委托实例也是相同的。
是否可以将转发器绑定到实例的供应商,以便拦截的方法转发给它?怎么可能做到这一点?