JDK8/Java8源码在线阅读

/*
 * Copyright (c) 1998, 2010, 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 sun.net;

import java.security.PrivilegedAction;
import java.security.Security;

public final class InetAddressCachePolicy {

    // Controls the cache policy for successful lookups only
    private static final String cachePolicyProp = "networkaddress.cache.ttl";
    private static final String cachePolicyPropFallback =
        "sun.net.inetaddr.ttl";

    // Controls the cache policy for negative lookups only
    private static final String negativeCachePolicyProp =
        "networkaddress.cache.negative.ttl";
    private static final String negativeCachePolicyPropFallback =
        "sun.net.inetaddr.negative.ttl";

    public static final int FOREVER = -1;
    public static final int NEVER = 0;

    /* default value for positive lookups */
    public static final int DEFAULT_POSITIVE = 30;

    /* The Java-level namelookup cache policy for successful lookups:
     *
     * -1: caching forever
     * any positive value: the number of seconds to cache an address for
     *
     * default value is forever (FOREVER), as we let the platform do the
     * caching. For security reasons, this caching is made forever when
     * a security manager is set.
     */
    private static int cachePolicy = FOREVER;

    /* The Java-level namelookup cache policy for negative lookups:
     *
     * -1: caching forever
     * any positive value: the number of seconds to cache an address for
     *
     * default value is 0. It can be set to some other value for
     * performance reasons.
     */
    private static int negativeCachePolicy = NEVER;

    /*
     * Whether or not the cache policy for successful lookups was set
     * using a property (cmd line).
     */
    private static boolean propertySet;

    /*
     * Whether or not the cache policy for negative lookups was set
     * using a property (cmd line).
     */
    private static boolean propertyNegativeSet;

    /*
     * Initialize
     */
    static {

        Integer tmp = java.security.AccessController.doPrivileged(
          new PrivilegedAction<Integer>() {
            public Integer run() {
                try {
                    String tmpString = Security.getProperty(cachePolicyProp);
                    if (tmpString != null) {
                        return Integer.valueOf(tmpString);
                    }
                } catch (NumberFormatException ignored) {
                    // Ignore
                }

                try {
                    String tmpString = System.getProperty(cachePolicyPropFallback);
                    if (tmpString != null) {
                        return Integer.decode(tmpString);
                    }
                } catch (NumberFormatException ignored) {
                    // Ignore
                }
                return null;
            }
          });

        if (tmp != null) {
            cachePolicy = tmp.intValue();
            if (cachePolicy < 0) {
                cachePolicy = FOREVER;
            }
            propertySet = true;
        } else {
            /* No properties defined for positive caching. If there is no
             * security manager then use the default positive cache value.
             */
            if (System.getSecurityManager() == null) {
                cachePolicy = DEFAULT_POSITIVE;
            }
        }
        tmp = java.security.AccessController.doPrivileged (
          new PrivilegedAction<Integer>() {
            public Integer run() {
                try {
                    String tmpString = Security.getProperty(negativeCachePolicyProp);
                    if (tmpString != null) {
                        return Integer.valueOf(tmpString);
                    }
                } catch (NumberFormatException ignored) {
                    // Ignore
                }

                try {
                    String tmpString = System.getProperty(negativeCachePolicyPropFallback);
                    if (tmpString != null) {
                        return Integer.decode(tmpString);
                    }
                } catch (NumberFormatException ignored) {
                    // Ignore
                }
                return null;
            }
          });

        if (tmp != null) {
            negativeCachePolicy = tmp.intValue();
            if (negativeCachePolicy < 0) {
                negativeCachePolicy = FOREVER;
            }
            propertyNegativeSet = true;
        }
    }

    public static synchronized int get() {
        return cachePolicy;
    }

    public static synchronized int getNegative() {
        return negativeCachePolicy;
    }

    /**
     * Sets the cache policy for successful lookups if the user has not
     * already specified a cache policy for it using a
     * command-property.
     * @param newPolicy the value in seconds for how long the lookup
     * should be cached
     */
    public static synchronized void setIfNotSet(int newPolicy) {
        /*
         * When setting the new value we may want to signal that the
         * cache should be flushed, though this doesn't seem strictly
         * necessary.
         */
        if (!propertySet) {
            checkValue(newPolicy, cachePolicy);
            cachePolicy = newPolicy;
        }
    }

    /**
     * Sets the cache policy for negative lookups if the user has not
     * already specified a cache policy for it using a
     * command-property.
     * @param newPolicy the value in seconds for how long the lookup
     * should be cached
     */
    public static synchronized void setNegativeIfNotSet(int newPolicy) {
        /*
         * When setting the new value we may want to signal that the
         * cache should be flushed, though this doesn't seem strictly
         * necessary.
         */

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