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The Async Http Client Registry Extras.
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/*
 * Copyright (c) 2010-2014 Sonatype, Inc. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */
package org.asynchttpclient.extras.registry;

import org.asynchttpclient.AsyncHttpClient;
import org.asynchttpclient.config.AsyncHttpClientConfigHelper;

import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;

public class AsyncImplHelper {

    public static final String ASYNC_HTTP_CLIENT_IMPL_SYSTEM_PROPERTY = "org.async.http.client.impl";
    public static final String ASYNC_HTTP_CLIENT_REGISTRY_SYSTEM_PROPERTY = "org.async.http.client.registry.impl";

    /*
     * Returns the class specified by either a system property or a properties
     * file as the class to instantiated for the AsyncHttpClient. Returns null
     * if property is not found and throws an AsyncHttpClientImplException if
     * the specified class couldn't be created.
     */
    public static Class getAsyncImplClass(String propertyName) {
        String asyncHttpClientImplClassName = AsyncHttpClientConfigHelper.getAsyncHttpClientConfig().getString(propertyName);
        if (asyncHttpClientImplClassName != null) {
            Class asyncHttpClientImplClass = AsyncImplHelper.getClass(asyncHttpClientImplClassName);
            return asyncHttpClientImplClass;
        }
        return null;
    }

    private static Class getClass(final String asyncImplClassName) {
        try {
            return AccessController.doPrivileged(new PrivilegedExceptionAction>() {
                @SuppressWarnings("unchecked")
                public Class run() throws ClassNotFoundException {
                    ClassLoader cl = Thread.currentThread().getContextClassLoader();
                    if (cl != null)
                        try {
                            return (Class) cl.loadClass(asyncImplClassName);
                        } catch (ClassNotFoundException e) {
                            AsyncHttpClientFactory.logger.info("Couldn't find class : " + asyncImplClassName + " in thread context classpath " + "checking system class path next",
                                    e);
                        }

                    cl = ClassLoader.getSystemClassLoader();
                    return (Class) cl.loadClass(asyncImplClassName);
                }
            });
        } catch (PrivilegedActionException e) {
            throw new AsyncHttpClientImplException("Class : " + asyncImplClassName + " couldn't be found in " + " the classpath due to : " + e.getMessage(), e);
        }
    }
}