--- /dev/null
+/*-
+ * ============LICENSE_START=======================================================
+ * ONAP : APPC
+ * ================================================================================
+ * Copyright (C) 2017-2018 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * Copyright (C) 2017 Amdocs
+ * =============================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.appc.pool;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * This class is used as a "wrapper" for any closeable elements that are cached in a pool. It is
+ * implemented as a dynamic proxy, so that it appears to be the same class of object to the client
+ * as the interface being cached. The generic type being cached MUST be an interface.
+ *
+ * @param <T> The generic type that we create a cached element for. This type is used to wrap
+ * instances of this type and expose access to the {@link java.io.Closeable} interface by
+ * using a dynamic proxy.
+ */
+
+public class CachedElement<T extends Closeable>
+ implements Closeable, InvocationHandler, CacheManagement {
+
+ /**
+ * The pool that is managing this cached element
+ */
+ private Pool<T> pool;
+
+ /**
+ * The element that we are caching in the pool
+ */
+ private T element;
+
+ /**
+ * A thread-safe atomic indicator that tells us that the wrapped element has been released to
+ * the pool already, and not to do it again.
+ */
+ private AtomicBoolean released = new AtomicBoolean(false);
+
+ /**
+ * Create a new instance of a cached element dynamic proxy for use in the pool.
+ * <p>
+ * This returns an instance of the proxy to the caller that appears to be the same interface(s)
+ * as the object being cached. The dynamic proxy then intercepts all open and close semantics
+ * and directs that element to the pool.
+ * </p>
+ * <p>
+ * If the object being proxied does not implement the {@link CacheManagement} interface, then
+ * that interface is added to the dynamic proxy being created. This interface is actually
+ * implemented by the invocation handler (this object) for the proxy and allows direct access to
+ * the wrapped object inside the proxy.
+ * </p>
+ *
+ * @param pool The pool that we are caching these elements within
+ * @param element The element actually being cached
+ * @param interfaces The interface list of interfaces the element must implement (usually one)
+ * @return The dynamic proxy
+ */
+ @SuppressWarnings("unchecked")
+ public static <T extends Closeable> T newInstance(Pool<T> pool, T element,
+ Class<?>[] interfaces) {
+ ClassLoader cl = element.getClass().getClassLoader();
+ CachedElement<T> ce = new CachedElement<>(pool, element);
+ boolean found = false;
+ for (Class<?> intf : interfaces) {
+ if (intf.getName().equals(CacheManagement.class.getName())) {
+ found = true;
+ break;
+ }
+ }
+
+ int length = found ? interfaces.length : interfaces.length + 1;
+ Class<?>[] proxyInterfaces = new Class[length];
+ System.arraycopy(interfaces, 0, proxyInterfaces, 0, interfaces.length);
+
+ if (!found) {
+ proxyInterfaces[interfaces.length] = CacheManagement.class;
+ }
+
+ return (T) Proxy.newProxyInstance(cl, proxyInterfaces, ce);
+ }
+
+ /**
+ * Construct a cached element and assign it to the pool as a free element
+ *
+ * @param pool The pool that the element will be managed within
+ * @param element The element we are caching
+ */
+ @SuppressWarnings("unchecked")
+ public CachedElement(Pool<T> pool, T element) {
+ this.pool = pool;
+ this.element = element;
+
+ try {
+ pool.release((T) this);
+ } catch (PoolDrainedException e) {
+ e.printStackTrace();
+ }
+ }
+
+ /**
+ * This method delegates the close call to the actual wrapped element.
+ * <p>
+ * NOTE: This is not the same method that is called by the dynamic proxy. This method is in
+ * place to satisfy the signature of the {@link java.io.Closeable} interface. If it were to be
+ * called directly, then we will delegate the close to the underlying context. However, when the
+ * cached element is called as a synamic proxy, entry is in the
+ * {@link #invoke(Object, Method, Object[])} method.
+ * </p>
+ *
+ * @see java.io.Closeable#close()
+ */
+ @Override
+ public void close() throws IOException {
+ element.close();
+ }
+
+ /**
+ * This method is the magic part of dynamic proxies. When the caller makes a method call based
+ * on the interface being proxied, this method is given control. This informs us of the method
+ * and arguments of the call. The object reference is that of the dynamic proxy itself, which is
+ * us.
+ * <p>
+ * Here we will check to see if the user is trying to close the "element" (the dynamic proxy
+ * acts like the wrapped element). If he is, then we don't really close it, but instead release
+ * the element that we are wrapping back to the free pool. Once this has happened, we mark the
+ * element as "closed" (from the perspective of this dynamic proxy) so that we wont try to
+ * release it again.
+ * </p>
+ * <p>
+ * If the method is the <code>equals</code> method then we assume that we are comparing the
+ * cached element in one dynamic proxy to the cached element in another. We execute the
+ * comparison between the cached elements, and not the dynamic proxies themselves. This
+ * preserves the allusion to the caller that the dynamic proxy is the object being wrapped.
+ * </p>
+ * <p>
+ * For convenience, we also implement the <code>getWrappedObject</code> method so that the
+ * dynamic proxy can be called to obtain the actual wrapped object if desired. Note, to use this
+ * method, the caller would have to invoke it through reflection.
+ * </p>
+ * <p>
+ * If the method being invoked is not one that we intercept, then we simply delegate that method
+ * onto the wrapped object.
+ * </p>
+ *
+ * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object, java.lang.reflect.Method,
+ * java.lang.Object[])
+ */
+ @SuppressWarnings({"unchecked", "nls"})
+ @Override
+ public Object invoke(Object proxy, Method method, Object[] args) throws Exception {
+ Object result = null;
+
+ switch (method.getName()) {
+ case "close":
+ if (released.compareAndSet(false, true)) {
+ if (!pool.isDrained()) {
+ pool.release((T) proxy);
+ }
+ }
+ break;
+ case "equals":
+ CacheManagement cm = (CacheManagement) proxy;
+ T other = (T) cm.getWrappedObject();
+ result = element.equals(other);
+ break;
+ case "getWrappedObject":
+ return element;
+ default:
+ result = method.invoke(element, args);
+ break;
+ }
+
+ return result;
+ }
+
+ /**
+ * This method is used to be able to access the wrapped object underneath the dynamic proxy
+ *
+ * @see org.onap.appc.pool.CacheManagement#getWrappedObject()
+ */
+ @Override
+ public T getWrappedObject() {
+ return element;
+ }
+
+ @SuppressWarnings("nls")
+ @Override
+ public String toString() {
+ return element == null ? "null" : element.toString();
+ }
+}
Code Review / appc.git / blobdiff