2 * ============LICENSE_START=======================================================
4 * ================================================================================
5 * Copyright (C) 2017-2018 AT&T Intellectual Property. All rights reserved.
6 * ================================================================================
7 * Copyright (C) 2017 Amdocs
8 * =============================================================================
9 * Licensed under the Apache License, Version 2.0 (the "License");
10 * you may not use this file except in compliance with the License.
11 * You may obtain a copy of the License at
13 * http://www.apache.org/licenses/LICENSE-2.0
15 * Unless required by applicable law or agreed to in writing, software
16 * distributed under the License is distributed on an "AS IS" BASIS,
17 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18 * See the License for the specific language governing permissions and
19 * limitations under the License.
21 * ============LICENSE_END=========================================================
24 package org.onap.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
35 * implemented as a dynamic proxy, so that it appears to be the same class of object to the client
36 * as the interface being cached. The generic type being cached MUST be an interface.
38 * @param <T> The generic type that we create a cached element for. This type is used to wrap
39 * instances of this type and expose access to the {@link java.io.Closeable} interface by
40 * using a dynamic proxy.
43 public class CachedElement<T extends Closeable>
44 implements Closeable, InvocationHandler, CacheManagement {
47 * The pool that is managing this cached element
52 * The element that we are caching in the pool
57 * A thread-safe atomic indicator that tells us that the wrapped element has been released to
58 * the pool already, and not to do it again.
60 private AtomicBoolean released = new AtomicBoolean(false);
63 * Create a new instance of a cached element dynamic proxy for use in the pool.
65 * This returns an instance of the proxy to the caller that appears to be the same interface(s)
66 * as the object being cached. The dynamic proxy then intercepts all open and close semantics
67 * and directs that element to the pool.
70 * If the object being proxied does not implement the {@link CacheManagement} interface, then
71 * that interface is added to the dynamic proxy being created. This interface is actually
72 * implemented by the invocation handler (this object) for the proxy and allows direct access to
73 * the wrapped object inside the proxy.
76 * @param pool The pool that we are caching these elements within
77 * @param element The element actually being cached
78 * @param interfaces The interface list of interfaces the element must implement (usually one)
79 * @return The dynamic proxy
81 @SuppressWarnings("unchecked")
82 public static <T extends Closeable> T newInstance(Pool<T> pool, T element,
83 Class<?>[] interfaces) {
84 ClassLoader cl = element.getClass().getClassLoader();
85 CachedElement<T> ce = new CachedElement<>(pool, element);
86 boolean found = false;
87 for (Class<?> intf : interfaces) {
88 if (intf.getName().equals(CacheManagement.class.getName())) {
94 int length = found ? interfaces.length : interfaces.length + 1;
95 Class<?>[] proxyInterfaces = new Class[length];
96 System.arraycopy(interfaces, 0, proxyInterfaces, 0, interfaces.length);
99 proxyInterfaces[interfaces.length] = CacheManagement.class;
102 return (T) Proxy.newProxyInstance(cl, proxyInterfaces, ce);
106 * Construct a cached element and assign it to the pool as a free element
108 * @param pool The pool that the element will be managed within
109 * @param element 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
127 * place to satisfy the signature of the {@link java.io.Closeable} interface. If it were to be
128 * called directly, then we will delegate the close to the underlying context. However, when the
129 * cached element is called as a synamic proxy, entry is in the
130 * {@link #invoke(Object, Method, Object[])} method.
133 * @see java.io.Closeable#close()
136 public void close() throws IOException {
141 * This method is the magic part of dynamic proxies. When the caller makes a method call based
142 * on the interface being proxied, this method is given control. This informs us of the method
143 * and arguments of the call. The object reference is that of the dynamic proxy itself, which is
146 * Here we will check to see if the user is trying to close the "element" (the dynamic proxy
147 * acts like the wrapped element). If he is, then we don't really close it, but instead release
148 * the element that we are wrapping back to the free pool. Once this has happened, we mark the
149 * element as "closed" (from the perspective of this dynamic proxy) so that we wont try to
153 * If the method is the <code>equals</code> method then we assume that we are comparing the
154 * cached element in one dynamic proxy to the cached element in another. We execute the
155 * comparison between the cached elements, and not the dynamic proxies themselves. This
156 * preserves the allusion to the caller that the dynamic proxy is the object being wrapped.
159 * For convenience, we also implement the <code>getWrappedObject</code> method so that the
160 * dynamic proxy can be called to obtain the actual wrapped object if desired. Note, to use this
161 * method, the caller would have to invoke it through reflection.
164 * If the method being invoked is not one that we intercept, then we simply delegate that method
165 * onto the wrapped object.
168 * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object, java.lang.reflect.Method,
169 * java.lang.Object[])
171 @SuppressWarnings({"unchecked", "nls"})
173 public Object invoke(Object proxy, Method method, Object[] args) throws Exception {
174 Object result = null;
176 switch (method.getName()) {
178 if (released.compareAndSet(false, true)) {
179 if (!pool.isDrained()) {
180 pool.release((T) proxy);
185 CacheManagement cm = (CacheManagement) proxy;
186 T other = (T) cm.getWrappedObject();
187 result = element.equals(other);
189 case "getWrappedObject":
192 result = method.invoke(element, args);
200 * This method is used to be able to access the wrapped object underneath the dynamic proxy
202 * @see org.onap.appc.pool.CacheManagement#getWrappedObject()
205 public T getWrappedObject() {
209 @SuppressWarnings("nls")
211 public String toString() {
212 return element == null ? "null" : element.toString();