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	/*
	* Copyright (c) 2003, 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 java.net;

	import java.io.IOException;
	import java.util.List;
	import sun.security.util.SecurityConstants;

	/**
	* Selects the proxy server to use, if any, when connecting to the
	* network resource referenced by a URL. A proxy selector is a
	* concrete sub-class of this class and is registered by invoking the
	* {@link java.net.ProxySelector#setDefault setDefault} method. The
	* currently registered proxy selector can be retrieved by calling
	* {@link java.net.ProxySelector#getDefault getDefault} method.
	*
	* <p> When a proxy selector is registered, for instance, a subclass
	* of URLConnection class should call the {@link #select select}
	* method for each URL request so that the proxy selector can decide
	* if a direct, or proxied connection should be used. The {@link
	* #select select} method returns an iterator over a collection with
	* the preferred connection approach.
	*
	* <p> If a connection cannot be established to a proxy (PROXY or
	* SOCKS) servers then the caller should call the proxy selector's
	* {@link #connectFailed connectFailed} method to notify the proxy
	* selector that the proxy server is unavailable. </p>
	*
	* <P>The default proxy selector does enforce a
	* <a href="doc-files/net-properties.html#Proxies">set of System Properties</a>
	* related to proxy settings.</P>
	*
	* @author Yingxian Wang
	* @author Jean-Christophe Collet
	* @since 1.5
	*/
	public abstract class ProxySelector {
	/**
	* The system wide proxy selector that selects the proxy server to
	* use, if any, when connecting to a remote object referenced by
	* an URL.
	*
	* @see #setDefault(ProxySelector)
	*/
	private static ProxySelector theProxySelector;

	static {
	try {
	Class<?> c = Class.forName("sun.net.spi.DefaultProxySelector");
	if (c != null && ProxySelector.class.isAssignableFrom(c)) {
	theProxySelector = (ProxySelector) c.newInstance();
	}
	} catch (Exception e) {
	theProxySelector = null;
	}
	}

	/**
	* Gets the system-wide proxy selector.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link NetPermission}{@code ("getProxySelector")}
	* @see #setDefault(ProxySelector)
	* @return the system-wide {@code ProxySelector}
	* @since 1.5
	*/
	public static ProxySelector getDefault() {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(SecurityConstants.GET_PROXYSELECTOR_PERMISSION);
	}
	return theProxySelector;
	}

	/**
	* Sets (or unsets) the system-wide proxy selector.
	*
	* Note: non-standard protocol handlers may ignore this setting.
	*
	* @param ps The HTTP proxy selector, or
	* {@code null} to unset the proxy selector.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link NetPermission}{@code ("setProxySelector")}
	*
	* @see #getDefault()
	* @since 1.5
	*/
	public static void setDefault(ProxySelector ps) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	sm.checkPermission(SecurityConstants.SET_PROXYSELECTOR_PERMISSION);
	}
	theProxySelector = ps;
	}

	/**
	* Selects all the applicable proxies based on the protocol to
	* access the resource with and a destination address to access
	* the resource at.
	* The format of the URI is defined as follow:
	* <UL>
	* <LI>http URI for http connections</LI>
	* <LI>https URI for https connections
	* <LI>{@code socket://host:port}<br>
	* for tcp client sockets connections</LI>
	* </UL>
	*
	* @param uri
	* The URI that a connection is required to
	*
	* @return a List of Proxies. Each element in the
	* the List is of type
	* {@link java.net.Proxy Proxy};
	* when no proxy is available, the list will
	* contain one element of type
	* {@link java.net.Proxy Proxy}
	* that represents a direct connection.
	* @throws IllegalArgumentException if the argument is null
	*/
	public abstract List<Proxy> select(URI uri);

	/**
	* Called to indicate that a connection could not be established
	* to a proxy/socks server. An implementation of this method can
	* temporarily remove the proxies or reorder the sequence of
	* proxies returned by {@link #select(URI)}, using the address
	* and the IOException caught when trying to connect.
	*
	* @param uri
	* The URI that the proxy at sa failed to serve.
	* @param sa
	* The socket address of the proxy/SOCKS server
	*
	* @param ioe
	* The I/O exception thrown when the connect failed.
	* @throws IllegalArgumentException if either argument is null
	*/
	public abstract void connectFailed(URI uri, SocketAddress sa, IOException ioe);
	}

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