/*

 * Copyright 2003-2006 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.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}<tt>("getProxySelector")</tt>

     * @see #setDefault(ProxySelector)

     * @return the system-wide <code>ProxySelector</code>

     * @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</code> to unset the proxy selector.

     *

     * @throws  SecurityException

     *          If a security manager has been installed and it denies

     * {@link NetPermission}<tt>("setProxySelector")</tt>

     *

     * @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>ftp URI for ftp connections</LI>

     * <LI><code>socket://host:port</code><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);

}