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/*-
* ============LICENSE_START=======================================================
* openECOMP : APP-C
* ================================================================================
* Copyright (C) 2017 AT&T Intellectual Property. All rights
* reserved.
* ================================================================================
* 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.openecomp.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 Throwable {
Object result = null;
if (method.getName().equals("close")) {
if (released.compareAndSet(false, true)) {
if (!pool.isDrained()) {
pool.release((T) proxy);
}
}
} else if (method.getName().equals("equals")) {
CacheManagement cm = (CacheManagement) proxy;
T other = (T) cm.getWrappedObject();
result = element.equals(other);
} else if (method.getName().equals("getWrappedObject")) {
return element;
} else {
result = method.invoke(element, args);
}
return result;
}
/**
* This method is used to be able to access the wrapped object underneath the dynamic proxy
*
* @see org.openecomp.appc.pool.CacheManagement#getWrappedObject()
*/
@Override
public T getWrappedObject() {
return element;
}
@SuppressWarnings("nls")
@Override
public String toString() {
return element == null ? "null" : element.toString();
}
}
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