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	/*
	* Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.net.httpserver.spi;

	import java.io.IOException;
	import java.net.*;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.util.Iterator;
	import java.util.ServiceLoader;
	import java.util.ServiceConfigurationError;
	import com.sun.net.httpserver.*;

	/**
	* Service provider class for HttpServer.
	* Sub-classes of HttpServerProvider provide an implementation of
	* {@link HttpServer} and associated classes. Applications do not normally use
	* this class. See {@link #provider()} for how providers are found and loaded.
	*/
	@jdk.Exported
	public abstract class HttpServerProvider {

	/**
	* creates a HttpServer from this provider
	*
	* @param addr
	* the address to bind to. May be {@code null}
	*
	* @param backlog
	* the socket backlog. A value of {@code zero} means the systems default
	*/
	public abstract HttpServer createHttpServer(InetSocketAddress addr,
	int backlog)
	throws IOException;

	/**
	* creates a HttpsServer from this provider
	*
	* @param addr
	* the address to bind to. May be {@code null}
	*
	* @param backlog
	* the socket backlog. A value of {@code zero} means the systems default
	*/
	public abstract HttpsServer createHttpsServer(InetSocketAddress addr,
	int backlog)
	throws IOException;

	private static final Object lock = new Object();
	private static HttpServerProvider provider = null;

	/**
	* Initializes a new instance of this class.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link RuntimePermission}{@code ("httpServerProvider")}
	*/
	protected HttpServerProvider() {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null)
	sm.checkPermission(new RuntimePermission("httpServerProvider"));
	}

	private static boolean loadProviderFromProperty() {
	String cn = System.getProperty("com.sun.net.httpserver.HttpServerProvider");
	if (cn == null)
	return false;
	try {
	Class<?> c = Class.forName(cn, true,
	ClassLoader.getSystemClassLoader());
	provider = (HttpServerProvider)c.newInstance();
	return true;
	} catch (ClassNotFoundException \|
	IllegalAccessException \|
	InstantiationException \|
	SecurityException x) {
	throw new ServiceConfigurationError(null, x);
	}
	}

	private static boolean loadProviderAsService() {
	Iterator<HttpServerProvider> i =
	ServiceLoader.load(HttpServerProvider.class,
	ClassLoader.getSystemClassLoader())
	.iterator();
	for (;;) {
	try {
	if (!i.hasNext())
	return false;
	provider = i.next();
	return true;
	} catch (ServiceConfigurationError sce) {
	if (sce.getCause() instanceof SecurityException) {
	// Ignore the security exception, try the next provider
	continue;
	}
	throw sce;
	}
	}
	}

	/**
	* Returns the system wide default HttpServerProvider for this invocation of
	* the Java virtual machine.
	*
	* <p> The first invocation of this method locates the default provider
	* object as follows: </p>
	*
	* <ol>
	*
	* <li><p> If the system property
	* {@code com.sun.net.httpserver.HttpServerProvider} is defined then it
	* is taken to be the fully-qualified name of a concrete provider class.
	* The class is loaded and instantiated; if this process fails then an
	* unspecified unchecked error or exception is thrown. </p></li>
	*
	* <li><p> If a provider class has been installed in a jar file that is
	* visible to the system class loader, and that jar file contains a
	* provider-configuration file named
	* {@code com.sun.net.httpserver.HttpServerProvider} in the resource
	* directory <tt>META-INF/services</tt>, then the first class name
	* specified in that file is taken. The class is loaded and
	* instantiated; if this process fails then an unspecified unchecked error
	* or exception is thrown. </p></li>
	*
	* <li><p> Finally, if no provider has been specified by any of the above
	* means then the system-default provider class is instantiated and the
	* result is returned. </p></li>
	*
	* </ol>
	*
	* <p> Subsequent invocations of this method return the provider that was
	* returned by the first invocation. </p>
	*
	* @return The system-wide default HttpServerProvider
	*/
	public static HttpServerProvider provider () {
	synchronized (lock) {
	if (provider != null)
	return provider;
	return (HttpServerProvider)AccessController
	.doPrivileged(new PrivilegedAction<Object>() {
	public Object run() {
	if (loadProviderFromProperty())
	return provider;
	if (loadProviderAsService())
	return provider;
	provider = new sun.net.httpserver.DefaultHttpServerProvider();
	return provider;
	}
	});
	}
	}

	}

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