HDFS-13979. Review StateStoreFileSystemImpl Class. Contributed by BELUGA BEHR.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/driver/impl/StateStoreFileSystemImpl.java

@@ -24,7 +24,8 @@ import java.io.InputStreamReader;
 import java.io.OutputStreamWriter;
 import java.net.URI;
 import java.nio.charset.StandardCharsets;
-import java.util.LinkedList;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 import org.apache.hadoop.fs.FSDataInputStream;
@@ -33,8 +34,8 @@ import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Options;
 import org.apache.hadoop.fs.Path;
-import org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
 import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
 import org.slf4j.Logger;
@@ -50,13 +51,13 @@ public class StateStoreFileSystemImpl extends StateStoreFileBaseImpl {
   private static final Logger LOG =
       LoggerFactory.getLogger(StateStoreFileSystemImpl.class);
 
-
   /** Configuration keys. */
   public static final String FEDERATION_STORE_FS_PATH =
       RBFConfigKeys.FEDERATION_STORE_PREFIX + "driver.fs.path";
 
   /** File system to back the State Store. */
   private FileSystem fs;
+
   /** Working path in the filesystem. */
   private String workPath;
 
@@ -141,7 +142,7 @@ public class StateStoreFileSystemImpl extends StateStoreFileBaseImpl {
           new InputStreamReader(fdis, StandardCharsets.UTF_8);
       reader = new BufferedReader(isr);
     } catch (IOException ex) {
-      LOG.error("Cannot open read stream for {}", path);
+      LOG.error("Cannot open read stream for {}", path, ex);
     }
     return reader;
   }
@@ -156,25 +157,26 @@ public class StateStoreFileSystemImpl extends StateStoreFileBaseImpl {
           new OutputStreamWriter(fdos, StandardCharsets.UTF_8);
       writer = new BufferedWriter(osw);
     } catch (IOException ex) {
-      LOG.error("Cannot open write stream for {}", path);
+      LOG.error("Cannot open write stream for {}", path, ex);
     }
     return writer;
   }
 
   @Override
   protected List<String> getChildren(String pathName) {
-    List<String> ret = new LinkedList<>();
     Path path = new Path(workPath, pathName);
     try {
       FileStatus[] files = fs.listStatus(path);
+      List<String> ret = new ArrayList<>(files.length);
       for (FileStatus file : files) {
         Path filePath = file.getPath();
         String fileName = filePath.getName();
         ret.add(fileName);
       }
+      return ret;
     } catch (Exception e) {
       LOG.error("Cannot get children for {}", pathName, e);
+      return Collections.emptyList();
     }
-    return ret;
   }
 }