HDFS-13511. Provide specialized exception when block length cannot be obtained. Contributed by Gabor Bota.

(cherry picked from commit 774c1f199e11d886d0c0a1069325f0284da35deb)
(cherry picked from commit 3b646a98365f0e7fb0690df63b1da6f7270c6e71)
(cherry picked from commit d675a955e244ae60139742bce806c0411d78576d)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/CannotObtainBlockLengthException.java

@@ -0,0 +1,55 @@
+/**
+ * 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;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+
+import java.io.IOException;
+
+/**
+ * This exception is thrown when the length of a LocatedBlock instance
+ * can not be obtained.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Unstable
+public class CannotObtainBlockLengthException extends IOException {
+  private static final long serialVersionUID = 1L;
+
+  public CannotObtainBlockLengthException() {
+    super();
+  }
+
+  public CannotObtainBlockLengthException(String message){
+    super(message);
+  }
+
+  /**
+   * Constructs an {@code CannotObtainBlockLengthException} with the
+   * specified LocatedBlock that failed to obtain block length.
+   *
+   * @param locatedBlock
+   *        The LocatedBlock instance which block length can not be obtained
+   */
+  public CannotObtainBlockLengthException(LocatedBlock locatedBlock) {
+    super("Cannot obtain block length for " + locatedBlock);
+  }
+
+}

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -451,7 +451,7 @@ public class DFSInputStream extends FSInputStream
       return 0;
     }
 
-    throw new IOException("Cannot obtain block length for " + locatedblock);
+    throw new CannotObtainBlockLengthException(locatedblock);
   }
 
   public long getFileLength() {