JDK8/Java8源码在线阅读

/*
 * Copyright (c) 2002, 2012, 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
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 */

package sun.security.ssl;

import java.util.*;

/**
 * A list of ProtocolVersions. Also maintains the list of supported protocols.
 * Instances of this class are immutable. Some member variables are final
 * and can be accessed directly without method accessors.
 *
 * @author  Andreas Sterbenz
 * @since   1.4.1
 */
final class ProtocolList {

    // the sorted protocol version list
    private final ArrayList<ProtocolVersion> protocols;

    private String[] protocolNames;

    // the minimum and maximum ProtocolVersions in this list
    final ProtocolVersion min, max;

    // the format for the hello version to use
    final ProtocolVersion helloVersion;

    ProtocolList(String[] names) {
        this(convert(names));
    }

    ProtocolList(ArrayList<ProtocolVersion> versions) {
        this.protocols = versions;

        if ((protocols.size() == 1) &&
                protocols.contains(ProtocolVersion.SSL20Hello)) {
            throw new IllegalArgumentException("SSLv2Hello cannot be " +
                "enabled unless at least one other supported version " +
                "is also enabled.");
        }

        if (protocols.size() != 0) {
            Collections.sort(protocols);
            min = protocols.get(0);
            max = protocols.get(protocols.size() - 1);
            helloVersion = protocols.get(0);
        } else {
            min = ProtocolVersion.NONE;
            max = ProtocolVersion.NONE;
            helloVersion = ProtocolVersion.NONE;
        }
    }

    private static ArrayList<ProtocolVersion> convert(String[] names) {
        if (names == null) {
            throw new IllegalArgumentException("Protocols may not be null");
        }

        ArrayList<ProtocolVersion> versions = new ArrayList<>(names.length);
        for (int i = 0; i < names.length; i++ ) {
            ProtocolVersion version = ProtocolVersion.valueOf(names[i]);
            if (versions.contains(version) == false) {
                versions.add(version);
            }
        }

        return versions;
    }

    /**
     * Return whether this list contains the specified protocol version.
     * SSLv2Hello is not a real protocol version we support, we always
     * return false for it.
     */
    boolean contains(ProtocolVersion protocolVersion) {
        if (protocolVersion == ProtocolVersion.SSL20Hello) {
            return false;
        }
        return protocols.contains(protocolVersion);
    }

    /**
     * Return a reference to the internal Collection of CipherSuites.
     * The Collection MUST NOT be modified.
     */
    Collection<ProtocolVersion> collection() {
        return protocols;
    }

    /**
     * Select a protocol version from the list.
     *
     * Return the lower of the protocol version of that suggested by
     * the <code>protocolVersion</code> and the highest version of this
     * protocol list, or null if no protocol version is available.
     *
     * The method is used by TLS server to negotiated the protocol
     * version between client suggested protocol version in the
     * client hello and protocol versions supported by the server.
     */
    ProtocolVersion selectProtocolVersion(ProtocolVersion protocolVersion) {
        ProtocolVersion selectedVersion = null;
        for (ProtocolVersion pv : protocols) {
            if (pv.v > protocolVersion.v) {
                break;  // Safe to break here as this.protocols is sorted
            }
            selectedVersion = pv;
        }

        return selectedVersion;

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