1 files changed, 214 insertions, 0 deletions
diff --git a/appc-core/appc-common-bundle/java/org/onap/appc/pool/CachedElement.java b/appc-core/appc-common-bundle/java/org/onap/appc/pool/CachedElement.java
new file mode 100644
index 000000000..e9b2ffeae
--- /dev/null
+++ b/appc-core/appc-common-bundle/java/org/onap/appc/pool/CachedElement.java
@@ -0,0 +1,214 @@
+/*-
+ * ============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();
+    }
+}