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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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,

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 *

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 */

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)) {

                @SuppressWarnings("deprecation")

                ProxySelector tmp = (ProxySelector) c.newInstance();

                theProxySelector = tmp;

            }

        } 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 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 or if

     *         the protocol or host cannot be determined from the provided

     *         {@code uri}

     */

    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);

    /**

     * Returns a ProxySelector which uses the given proxy address for all HTTP

     * and HTTPS requests. If proxy is {@code null} then proxying is disabled.

     *

     * @param proxyAddress

     *        The address of the proxy

     *

     * @return a ProxySelector

     *

     * @since 9

     */

    public static ProxySelector of(InetSocketAddress proxyAddress) {

        return new StaticProxySelector(proxyAddress);

    }

    static class StaticProxySelector extends ProxySelector {

        private static final List<Proxy> NO_PROXY_LIST = List.of(Proxy.NO_PROXY);

        final List<Proxy> list;

        StaticProxySelector(InetSocketAddress address){

            Proxy p;

            if (address == null) {

                p = Proxy.NO_PROXY;

            } else {

                p = new Proxy(Proxy.Type.HTTP, address);

            }

            list = List.of(p);

        }

        @Override

        public void connectFailed(URI uri, SocketAddress sa, IOException e) {

            /* ignore */

        }

        @Override

        public synchronized List<Proxy> select(URI uri) {

            String scheme = uri.getScheme().toLowerCase();

            if (scheme.equals("http") || scheme.equals("https")) {

                return list;

            } else {

                return NO_PROXY_LIST;

            }

        }

    }

}