add file for HDFS-4817

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1526962 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/CachingStrategy.java

@@ -0,0 +1,64 @@
+/**
+ * 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.hdfs.server.datanode;
+
+/**
+ * The caching strategy we should use for an HDFS read or write operation.
+ */
+public class CachingStrategy {
+  private Boolean dropBehind; // null = use server defaults
+  private Long readahead; // null = use server defaults
+  
+  public static CachingStrategy newDefaultStrategy() {
+    return new CachingStrategy(null, null);
+  }
+
+  public static CachingStrategy newDropBehind() {
+    return new CachingStrategy(true, null);
+  }
+
+  public CachingStrategy duplicate() {
+    return new CachingStrategy(this.dropBehind, this.readahead);
+  }
+
+  public CachingStrategy(Boolean dropBehind, Long readahead) {
+    this.dropBehind = dropBehind;
+    this.readahead = readahead;
+  }
+
+  public Boolean getDropBehind() {
+    return dropBehind;
+  }
+  
+  public void setDropBehind(Boolean dropBehind) {
+    this.dropBehind = dropBehind;
+  }
+  
+  public Long getReadahead() {
+    return readahead;
+  }
+
+  public void setReadahead(Long readahead) {
+    this.readahead = readahead;
+  }
+
+  public String toString() {
+    return "CachingStrategy(dropBehind=" + dropBehind +
+        ", readahead=" + readahead + ")";
+  }
+}