HDFS-15506. [JDK 11] Fix javadoc errors in hadoop-hdfs module. Contributed by Xieming Li.

(cherry picked from commit 7938ebfb9d)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -682,7 +682,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
       600;
   /**
    * The maximum number of getBlocks RPCs data movement utilities can make to
-   * a NameNode per second. Values <= 0 disable throttling. This affects
+   * a NameNode per second. Values &lt;= 0 disable throttling. This affects
    * anything that uses a NameNodeConnector, i.e., the Balancer, Mover,
    * and StoragePolicySatisfier.
    */

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSUtil.java

@@ -39,7 +39,6 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.DataInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.PrintStream;
 import java.net.InetAddress;
@@ -1777,7 +1776,6 @@ public static DelegationTokenIdentifier decodeDelegationToken(
    *                                was found.
    * @throws ParentNotDirectoryException
    * @throws UnresolvedLinkException
-   * @throws FileNotFoundException
    */
   public static void checkProtectedDescendants(
       FSDirectory fsd, INodesInPath iip)

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

@@ -40,7 +40,7 @@
 /**
  * Checks to see if datanodes have finished DECOMMISSION_INPROGRESS or
  * ENTERING_MAINTENANCE state.
- * <p/>
+ * <p>
  * Since this is done while holding the namesystem lock,
  * the amount of work per monitor tick is limited.
  */

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/DirectorySnapshottableFeature.java

@@ -173,7 +173,8 @@ void addSnapshot(Snapshot snapshot) {
    * Add a snapshot.
    * @param snapshotRoot Root of the snapshot.
    * @param name Name of the snapshot.
-   * @param mtime The snapshot creation time set by Time.now().
+   * @param leaseManager
+   * @param captureOpenFiles
    * @throws SnapshotException Throw SnapshotException when there is a snapshot
    *           with the same name already exists or snapshot quota exceeds
    */

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

@@ -2184,7 +2184,6 @@ private static void printUsage(String cmd) {
 
   /**
    * @param argv The parameters passed to this program.
-   * @exception Exception if the filesystem does not exist.
    * @return 0 on success, non zero on error.
    */
   @Override