HDFS-14078. Admin helper fails to prettify NullPointerExceptions. Contributed by Elek, Marton.

Signed-off-by: Wei-Chiu Chuang <weichiu@apache.org>
(cherry picked from commit cc229be9ebb1b3737c9f5fcb29788b51fa584e47)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/AdminHelper.java

@@ -65,8 +65,14 @@ public class AdminHelper {
    * When it's a known error, pretty-print the error and squish the stack trace.
    */
   static String prettifyException(Exception e) {
+    if (e.getLocalizedMessage() != null) {
       return e.getClass().getSimpleName() + ": "
           + e.getLocalizedMessage().split("\n")[0];
+    } else if (e.getStackTrace() != null && e.getStackTrace().length > 0) {
+      return e.getClass().getSimpleName() + " at " + e.getStackTrace()[0];
+    } else {
+      return e.getClass().getSimpleName();
+    }
   }
 
   static TableListing getOptionDescriptionListing() {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestAdminHelper.java

@@ -0,0 +1,50 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.tools;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Test class to test Admin Helper.
+ */
+public class TestAdminHelper {
+
+  @Test
+  public void prettifyExceptionWithNpe() {
+    String pretty = AdminHelper.prettifyException(new NullPointerException());
+    Assert.assertTrue(
+        "Prettified exception message doesn't contain the required exception "
+            + "message",
+        pretty.startsWith("NullPointerException at org.apache.hadoop.hdfs.tools"
+            + ".TestAdminHelper.prettifyExceptionWithNpe"));
+  }
+
+  @Test
+  public void prettifyException() {
+
+    String pretty = AdminHelper.prettifyException(
+        new IllegalArgumentException("Something is wrong",
+            new IllegalArgumentException("Something is illegal")));
+
+    Assert.assertEquals(
+        "IllegalArgumentException: Something is wrong",
+        pretty);
+
+  }
+}