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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to you under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    * http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.hadoop.hbase.util;
18  
19  import java.lang.reflect.Method;
20  import java.net.UnknownHostException;
21  
22  import org.apache.hadoop.hbase.classification.InterfaceAudience;
23  
24  /**
25   * Wrapper around Hadoop's DNS class to hide reflection.
26   */
27  @InterfaceAudience.Private
28  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="REC_CATCH_EXCEPTION",
29    justification="If exception, presume HAS_NEW_DNS_GET_DEFAULT_HOST_API false")
30  public final class DNS {
31    private static boolean HAS_NEW_DNS_GET_DEFAULT_HOST_API;
32    private static Method GET_DEFAULT_HOST_METHOD;
33  
34    static {
35      try {
36        GET_DEFAULT_HOST_METHOD = org.apache.hadoop.net.DNS.class
37            .getMethod("getDefaultHost", String.class, String.class, boolean.class);
38        HAS_NEW_DNS_GET_DEFAULT_HOST_API = true;
39      } catch (Exception e) {
40        HAS_NEW_DNS_GET_DEFAULT_HOST_API = false; // FindBugs: Causes REC_CATCH_EXCEPTION. Suppressed
41      }
42    }
43  
44    private DNS() {}
45  
46    /**
47     * Wrapper around DNS.getDefaultHost(String, String), calling
48     * DNS.getDefaultHost(String, String, boolean) when available.
49     *
50     * @param strInterface The network interface to query.
51     * @param nameserver The DNS host name.
52     * @return The default host names associated with IPs bound to the network interface.
53     */
54    public static String getDefaultHost(String strInterface, String nameserver)
55        throws UnknownHostException {
56      if (HAS_NEW_DNS_GET_DEFAULT_HOST_API) {
57        try {
58          // Hadoop-2.8 includes a String, String, boolean variant of getDefaultHost
59          // which properly handles multi-homed systems with Kerberos.
60          return (String) GET_DEFAULT_HOST_METHOD.invoke(null, strInterface, nameserver, true);
61        } catch (Exception e) {
62          // If we can't invoke the method as it should exist, throw an exception
63          throw new RuntimeException("Failed to invoke DNS.getDefaultHost via reflection", e);
64        }
65      } else {
66        return org.apache.hadoop.net.DNS.getDefaultHost(strInterface, nameserver);
67      }
68    }
69  }