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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.hadoop.hbase.io.hfile;
19  
20  import java.io.IOException;
21  
22  import org.apache.hadoop.fs.FSDataInputStream;
23  
24  public class HFileUtil {
25  
26    /** guards against NullPointer
27     * utility which tries to seek on the DFSIS and will try an alternative source
28     * if the FSDataInputStream throws an NPE HBASE-17501
29     * @param istream
30     * @param offset
31     * @throws IOException
32     */
33    static public void seekOnMultipleSources(FSDataInputStream istream, long offset) throws IOException {
34      try {
35        // attempt to seek inside of current blockReader
36        istream.seek(offset);
37      } catch (NullPointerException e) {
38        // retry the seek on an alternate copy of the data
39        // this can occur if the blockReader on the DFSInputStream is null
40        istream.seekToNewSource(offset);
41      }
42    }
43  }