inetaddresscachepolicy.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 235 行

/*
 * @(#)InetAddressCachePolicy.java	1.14 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package sun.net;

import java.net.InetAddress;
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;

    /* 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;
    
    /* 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;

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

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

    /*
     * Initialize
     */
    static {

	set = false;
	negativeSet = false;

	cachePolicy = FOREVER;
	negativeCachePolicy =  0;

	Integer tmp = null;

	try {
	    tmp = new Integer(
              (String)java.security.AccessController.doPrivileged (
		new PrivilegedAction() {
		  public Object run() {
		      return Security.getProperty(cachePolicyProp);
		  }
	      }));
	} catch (NumberFormatException e) {
	    // ignore
	}
	if (tmp != null) {
	    cachePolicy = tmp.intValue();
	    if (cachePolicy < 0) {
		cachePolicy = FOREVER;
	    }
	    set = true;
	} else {
	    tmp = (Integer)java.security.AccessController.doPrivileged
		(new sun.security.action.GetIntegerAction(cachePolicyPropFallback));
	    if (tmp != null) {
		cachePolicy = tmp.intValue();
		if (cachePolicy < 0) {
		    cachePolicy = FOREVER;
		}
		set = true;
	    }
	}

	try {
	    tmp = new Integer(
              (String)java.security.AccessController.doPrivileged (
		new PrivilegedAction() {
		  public Object run() {
		      return Security.getProperty(negativeCachePolicyProp);
		  }
	      }));
	} catch (NumberFormatException e) {
	    // ignore
	}

	if (tmp != null) {
	    negativeCachePolicy = tmp.intValue();
	    if (negativeCachePolicy < 0) {
		negativeCachePolicy = FOREVER;
	    }
	    negativeSet = true;
	} else {
	    tmp = (Integer)java.security.AccessController.doPrivileged
		(new sun.security.action.GetIntegerAction(negativeCachePolicyPropFallback));
	    if (tmp != null) {
		negativeCachePolicy = tmp.intValue();
		if (negativeCachePolicy < 0) {
		    negativeCachePolicy = FOREVER;
		}
		negativeSet = 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 (!set) {
	    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.
	 */
	
	if (!negativeSet) {
	    // Negative caching does not seem to have any security
	    // implications.
 	    // checkValue(newPolicy, negativeCachePolicy);
	    negativeCachePolicy = newPolicy;
	}
    }

    private static void checkValue(int newPolicy, int oldPolicy) {

	/*
	 * If malicious code gets a hold of this method, prevent
	 * setting the cache policy to something laxer or some
	 * invalid negative value.
	 */

	if (newPolicy == FOREVER)
	    return;

	if ((oldPolicy == FOREVER) ||
	    (newPolicy < oldPolicy) ||
	    (newPolicy < FOREVER)) {
	    
	    throw new 
		SecurityException("can't make InetAddress cache more lax");
	    
	}
    }
}