HDFS-15978. Solve DatanodeManager#getBlockRecoveryCommand() printing IOException. (#2913) Contributed by JiangHua Zhu.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java

@@ -1658,7 +1658,7 @@ public class DatanodeManager {
       BlockUnderConstructionFeature uc = b.getUnderConstructionFeature();
       if(uc == null) {
         throw new IOException("Recovery block " + b +
-            "where it is not under construction.");
+            " where it is not under construction.");
       }
       final DatanodeStorageInfo[] storages = uc.getExpectedStorageLocations();
       // Skip stale nodes during recovery