HADOOP-12252. LocalDirAllocator should not throw NPE with empty string configuration. Contributed by Zhihai Xu

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -1084,6 +1084,9 @@ Release 2.8.0 - UNRELEASED
     HADOOP-12386. RetryPolicies.RETRY_FOREVER should be able to specify a 
     retry interval. (Sunil G via wangda)
 
+    HADOOP-12252. LocalDirAllocator should not throw NPE with empty string
+    configuration. (Zhihai Xu)
+
   OPTIMIZATIONS
 
     HADOOP-12051. ProtobufRpcEngine.invoke() should use Exception.toString()

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/LocalDirAllocator.java

@@ -250,9 +250,9 @@ public class LocalDirAllocator {
     private int dirNumLastAccessed;
     private Random dirIndexRandomizer = new Random();
     private FileSystem localFS;
-    private DF[] dirDF;
+    private DF[] dirDF = new DF[0];
     private String contextCfgItemName;
-    private String[] localDirs;
+    private String[] localDirs = new String[0];
     private String savedLocalDirs = "";
 
     public AllocatorPerContext(String contextCfgItemName) {

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestLocalDirAllocator.java

@@ -26,6 +26,7 @@ import java.util.Iterator;
 import java.util.NoSuchElementException;
 
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.util.DiskChecker.DiskErrorException;
 import org.apache.hadoop.util.Shell;
 
 import org.junit.runner.RunWith;
@@ -312,7 +313,30 @@ public class TestLocalDirAllocator {
     } catch (IOException e) {
       assertEquals(CONTEXT + " not configured", e.getMessage());
     } catch (NullPointerException e) {
-      fail("Lack of configuration should not have thrown an NPE.");
+      fail("Lack of configuration should not have thrown a NPE.");
+    }
+
+    String  NEW_CONTEXT = CONTEXT + ".new";
+    conf1.set(NEW_CONTEXT, "");
+    LocalDirAllocator newDirAllocator = new LocalDirAllocator(NEW_CONTEXT);
+    try {
+      newDirAllocator.getLocalPathForWrite("/test", conf1);
+      fail("Exception not thrown when " + NEW_CONTEXT +
+          " is set to empty string");
+    } catch (IOException e) {
+      assertTrue(e instanceof DiskErrorException);
+    } catch (NullPointerException e) {
+      fail("Wrong configuration should not have thrown a NPE.");
+    }
+
+    try {
+      newDirAllocator.getLocalPathToRead("/test", conf1);
+      fail("Exception not thrown when " + NEW_CONTEXT +
+          " is set to empty string");
+    } catch (IOException e) {
+      assertTrue(e instanceof DiskErrorException);
+    } catch (NullPointerException e) {
+      fail("Wrong configuration should not have thrown a NPE.");
     }
   }