2 * ============LICENSE_START=======================================================
4 * ================================================================================
5 * Copyright (C) 2017 AT&T Intellectual Property. All rights
7 * ================================================================================
8 * Licensed under the Apache License, Version 2.0 (the "License");
9 * you may not use this file except in compliance with the License.
10 * You may obtain a copy of the License at
12 * http://www.apache.org/licenses/LICENSE-2.0
14 * Unless required by applicable law or agreed to in writing, software
15 * distributed under the License is distributed on an "AS IS" BASIS,
16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17 * See the License for the specific language governing permissions and
18 * limitations under the License.
19 * ============LICENSE_END=========================================================
24 package org.openecomp.appc.pool;
26 import java.io.Closeable;
27 import java.io.IOException;
28 import java.lang.reflect.InvocationHandler;
29 import java.lang.reflect.Method;
30 import java.lang.reflect.Proxy;
31 import java.util.concurrent.atomic.AtomicBoolean;
34 * This class is used as a "wrapper" for any closeable elements that are cached in a pool. It is implemented as a
35 * dynamic proxy, so that it appears to be the same class of object to the client as the interface being cached. The
36 * generic type being cached MUST be an interface.
38 * The generic type that we create a cached element for. This type is used to wrap instances of this type and
39 * expose access to the {@link java.io.Closeable} interface by using a dynamic proxy.
42 public class CachedElement<T extends Closeable> implements Closeable, InvocationHandler, CacheManagement {
45 * The pool that is managing this cached element
50 * The element that we are caching in the pool
55 * A thread-safe atomic indicator that tells us that the wrapped element has been released to the pool already, and
58 private AtomicBoolean released = new AtomicBoolean(false);
61 * Create a new instance of a cached element dynamic proxy for use in the pool.
63 * This returns an instance of the proxy to the caller that appears to be the same interface(s) as the object being
64 * cached. The dynamic proxy then intercepts all open and close semantics and directs that element to the pool.
67 * If the object being proxied does not implement the {@link CacheManagement} interface, then that interface is
68 * added to the dynamic proxy being created. This interface is actually implemented by the invocation handler (this
69 * object) for the proxy and allows direct access to the wrapped object inside the proxy.
73 * The pool that we are caching these elements within
75 * The element actually being cached
77 * The interface list of interfaces the element must implement (usually one)
78 * @return The dynamic proxy
80 @SuppressWarnings("unchecked")
81 public static <T extends Closeable> T newInstance(Pool<T> pool, T element, Class<?>[] interfaces) {
82 ClassLoader cl = element.getClass().getClassLoader();
83 CachedElement<T> ce = new CachedElement<>(pool, element);
84 boolean found = false;
85 for (Class<?> intf : interfaces) {
86 if (intf.getName().equals(CacheManagement.class.getName())) {
92 int length = found ? interfaces.length : interfaces.length + 1;
93 Class<?>[] proxyInterfaces = new Class[length];
94 System.arraycopy(interfaces, 0, proxyInterfaces, 0, interfaces.length);
97 proxyInterfaces[interfaces.length] = CacheManagement.class;
100 return (T) Proxy.newProxyInstance(cl, proxyInterfaces, ce);
104 * Construct a cached element and assign it to the pool as a free element
107 * The pool that the element will be managed within
109 * The element we are caching
111 @SuppressWarnings("unchecked")
112 public CachedElement(Pool<T> pool, T element) {
114 this.element = element;
117 pool.release((T) this);
118 } catch (PoolDrainedException e) {
124 * This method delegates the close call to the actual wrapped element.
126 * NOTE: This is not the same method that is called by the dynamic proxy. This method is in place to satisfy the
127 * signature of the {@link java.io.Closeable} interface. If it were to be called directly, then we will delegate the
128 * close to the underlying context. However, when the cached element is called as a synamic proxy, entry is in the
129 * {@link #invoke(Object, Method, Object[])} method.
132 * @see java.io.Closeable#close()
135 public void close() throws IOException {
140 * This method is the magic part of dynamic proxies. When the caller makes a method call based on the interface
141 * being proxied, this method is given control. This informs us of the method and arguments of the call. The object
142 * reference is that of the dynamic proxy itself, which is us.
144 * Here we will check to see if the user is trying to close the "element" (the dynamic proxy acts like the wrapped
145 * element). If he is, then we don't really close it, but instead release the element that we are wrapping back to
146 * the free pool. Once this has happened, we mark the element as "closed" (from the perspective of this dynamic
147 * proxy) so that we wont try to release it again.
150 * If the method is the <code>equals</code> method then we assume that we are comparing the cached element in one
151 * dynamic proxy to the cached element in another. We execute the comparison between the cached elements, and not
152 * the dynamic proxies themselves. This preserves the allusion to the caller that the dynamic proxy is the object
156 * For convenience, we also implement the <code>getWrappedObject</code> method so that the dynamic proxy can be
157 * called to obtain the actual wrapped object if desired. Note, to use this method, the caller would have to invoke
158 * it through reflection.
161 * If the method being invoked is not one that we intercept, then we simply delegate that method onto the wrapped
165 * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[])
171 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
172 Object result = null;
174 if (method.getName().equals("close")) {
175 if (released.compareAndSet(false, true)) {
176 if (!pool.isDrained()) {
177 pool.release((T) proxy);
180 } else if (method.getName().equals("equals")) {
181 CacheManagement cm = (CacheManagement) proxy;
182 T other = (T) cm.getWrappedObject();
183 result = element.equals(other);
184 } else if (method.getName().equals("getWrappedObject")) {
187 result = method.invoke(element, args);
194 * This method is used to be able to access the wrapped object underneath the dynamic proxy
196 * @see org.openecomp.appc.pool.CacheManagement#getWrappedObject()
199 public T getWrappedObject() {
203 @SuppressWarnings("nls")
205 public String toString() {
206 return element == null ? "null" : element.toString();