HADOOP-3620. Added the file CacheDNSToSwitchMapping.java that was missed earlier.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/trunk@682593 13f79535-47bb-0310-9956-ffa450edef68

src/core/org/apache/hadoop/net/CachedDNSToSwitchMapping.java

@@ -0,0 +1,80 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.net;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * A cached implementation of DNSToSwitchMapping that takes an
+ * raw DNSToSwitchMapping and stores the resolved network location in 
+ * a cache. The following calls to a resolved network location
+ * will get its location from the cache. 
+ *
+ */
+public class CachedDNSToSwitchMapping implements DNSToSwitchMapping {
+  private Map<String, String> cache = new TreeMap<String, String>();
+  protected DNSToSwitchMapping rawMapping;
+  
+  public CachedDNSToSwitchMapping(DNSToSwitchMapping rawMapping) {
+    this.rawMapping = rawMapping;
+  }
+  
+  public List<String> resolve(List<String> names) {
+    // normalize all input names to be in the form of IP addresses
+    names = NetUtils.normalizeHostNames(names);
+    
+    List <String> result = new ArrayList<String>(names.size());
+    if (names.isEmpty()) {
+      return result;
+    }
+
+
+    // find out all names without cached resolved location
+    List<String> unCachedHosts = new ArrayList<String>(names.size());
+    for (String name : names) {
+      if (cache.get(name) == null) {
+        unCachedHosts.add(name);
+      } 
+    }
+    
+    // Resolve those names
+    List<String> rNames = rawMapping.resolve(unCachedHosts);
+    
+    // Cache the result
+    if (rNames != null) {
+      for (int i=0; i<unCachedHosts.size(); i++) {
+        cache.put(unCachedHosts.get(i), rNames.get(i));
+      }
+    }
+    
+    // Construct the result
+    for (String name : names) {
+      //now everything is in the cache
+      String networkLocation = cache.get(name);
+      if (networkLocation != null) {
+        result.add(networkLocation);
+      } else { //resolve all or nothing
+        return null;
+      }
+    }
+    return result;
+  }
+}