1 /*
   2  * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.net.dns;
  27 
  28 import java.util.List;
  29 import java.io.IOException;
  30 
  31 /**
  32  * The configuration of the client resolver.
  33  *
  34  * <p>A ResolverConfiguration is a singleton that represents the
  35  * configuration of the client resolver. The ResolverConfiguration
  36  * is opened by invoking the {@link #open() open} method.
  37  *
  38  * @since 1.4
  39  */
  40 
  41 public abstract class ResolverConfiguration {
  42 
  43     private static final Object lock = new Object();
  44 
  45     private static ResolverConfiguration provider;
  46 
  47     protected ResolverConfiguration() { }
  48 
  49     /**
  50      * Opens the resolver configuration.
  51      *
  52      * @return the resolver configuration
  53      */
  54     public static ResolverConfiguration open() {
  55         synchronized (lock) {
  56             if (provider == null) {
  57                 provider = new sun.net.dns.ResolverConfigurationImpl();
  58             }
  59             return provider;
  60         }
  61     }
  62 
  63     /**
  64      * Returns a list corresponding to the domain search path. The
  65      * list is ordered by the search order used for host name lookup.
  66      * Each element in the list returns a {@link java.lang.String}
  67      * containing a domain name or suffix.
  68      *
  69      * @return list of domain names
  70      */
  71     public abstract List searchlist();
  72 
  73     /**
  74      * Returns a list of name servers used for host name lookup.
  75      * Each element in the list returns a {@link java.lang.String}
  76      * containing the textual representation of the IP address of
  77      * the name server.
  78      *
  79      * @return list of the name servers
  80      */
  81     public abstract List nameservers();
  82 
  83 
  84     /**
  85      * Options representing certain resolver variables of
  86      * a {@link ResolverConfiguration}.
  87      */
  88     public static abstract class Options {
  89 
  90         /**
  91          * Returns the maximum number of attempts the resolver
  92          * will connect to each name server before giving up
  93          * and returning an error.
  94          *
  95          * @return the resolver attempts value or -1 is unknown
  96          */
  97         public int attempts() {
  98             return -1;
  99         }
 100 
 101         /**
 102          * Returns the basic retransmit timeout, in milliseconds,
 103          * used by the resolver. The resolver will typically use
 104          * an exponential backoff algorithm where the timeout is
 105          * doubled for every retransmit attempt. The basic
 106          * retransmit timeout, returned here, is the initial
 107          * timeout for the exponential backoff algorithm.
 108          *
 109          * @return the basic retransmit timeout value or -1
 110          *         if unknown
 111          */
 112         public int retrans() {
 113             return -1;
 114         }
 115     }
 116 
 117     /**
 118      * Returns the {@link #Options} for the resolver.
 119      *
 120      * @return options for the resolver
 121      */
 122     public abstract Options options();
 123 }