fix checkstyles, update the documents

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

@@ -247,7 +247,7 @@ private boolean checkSupportObserver(HAServiceTarget target) {
   }
 
   private int transitionToObserver(final CommandLine cmd)
-      throws IOException, ServiceFailedException {
+      throws IOException {
     String[] argv = cmd.getArgs();
     if (argv.length != 1) {
       errOut.println("transitionToObserver: incorrect number of arguments");
@@ -265,8 +265,8 @@ private int transitionToObserver(final CommandLine cmd)
     try {
       HAServiceProtocol proto = target.getProxy(getConf(), 0);
       HAServiceProtocolHelper.transitionToObserver(proto, createReqInfo());
-    } catch (IOException e) {
-      errOut.println("TransitionToObserver failed! " + e.getMessage());
+    } catch (ServiceFailedException e) {
+      errOut.println("transitionToObserver failed! " + e.getLocalizedMessage());
       return -1;
     }
     return 0;

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -3749,7 +3749,7 @@
   <name>dfs.ha.nn.not-become-active-in-safemode</name>
   <value>false</value>
   <description>
-    This will prevent safe mode namenodes to become active while other standby
+    This will prevent safe mode namenodes to become active or observer while other standby
     namenodes might be ready to serve requests when it is set to true.
   </description>
 </property>

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSHighAvailabilityWithNFS.md

@@ -316,12 +316,14 @@ The order in which you set these configurations is unimportant, but the values y
           <value>hdfs://mycluster</value>
         </property>
 
-*   **dfs.ha.nn.not-become-active-in-safemode** - if prevent safe mode namenodes to become active
-
-    Whether allow namenode to become active when it is in safemode, when it is
-    set to true, namenode in safemode will report SERVICE_UNHEALTHY to ZKFC if
-    auto failover is on, or will throw exception to fail the transition to
-    active if auto failover is off. For example:
+*   **dfs.ha.nn.not-become-active-in-safemode** - if prevent safe mode namenodes to become active or observer
+
+      Whether allow namenode to become active when it is in safemode, when it is
+      set to true, namenode in safemode will report SERVICE_UNHEALTHY to ZKFC if
+      auto failover is on, or will throw exception to fail the transition to
+      active if auto failover is off. If you transition namenode to observer state 
+      when it is in safemode, when this configuration is set to true, namenode will throw exception 
+      to fail the transition to observer. For example:
 
         <property>
           <name>dfs.ha.nn.not-become-active-in-safemode</name>

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSHighAvailabilityWithQJM.md

@@ -376,12 +376,14 @@ The order in which you set these configurations is unimportant, but the values y
           <value>/path/to/journal/node/local/data</value>
         </property>
 
-*   **dfs.ha.nn.not-become-active-in-safemode** - if prevent safe mode namenodes to become active
+*   **dfs.ha.nn.not-become-active-in-safemode** - if prevent safe mode namenodes to become active or observer
 
     Whether allow namenode to become active when it is in safemode, when it is
     set to true, namenode in safemode will report SERVICE_UNHEALTHY to ZKFC if
     auto failover is on, or will throw exception to fail the transition to
-    active if auto failover is off. For example:
+    active if auto failover is off. If you transition namenode to observer state
+    when it is in safemode, when this configuration is set to true, namenode will throw exception
+    to fail the transition to observer. For example:
 
         <property>
           <name>dfs.ha.nn.not-become-active-in-safemode</name>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/ha/TestHASafeMode.java

@@ -978,20 +978,15 @@ public void testTransitionToActiveWhenSafeMode() throws Exception {
     }
   }
 
-  /**
-   * Test transition to observer when namenode in safemode.
-   *
-   * @throws IOException
-   */
   @Test
   public void testTransitionToObserverWhenSafeMode() throws Exception {
     Configuration config = new Configuration();
     config.setBoolean(DFS_HA_NN_NOT_BECOME_ACTIVE_IN_SAFEMODE, true);
     try (MiniDFSCluster miniCluster = new MiniDFSCluster.Builder(config,
-            new File(GenericTestUtils.getRandomizedTempPath()))
-            .nnTopology(MiniDFSNNTopology.simpleHATopology())
-            .numDataNodes(1)
-            .build()) {
+        new File(GenericTestUtils.getRandomizedTempPath()))
+        .nnTopology(MiniDFSNNTopology.simpleHATopology())
+        .numDataNodes(1)
+        .build()) {
       miniCluster.waitActive();
       miniCluster.transitionToStandby(0);
       miniCluster.transitionToStandby(1);
@@ -1000,8 +995,8 @@ public void testTransitionToObserverWhenSafeMode() throws Exception {
       NameNodeAdapter.enterSafeMode(namenode0, false);
       NameNodeAdapter.enterSafeMode(namenode1, false);
       LambdaTestUtils.intercept(ServiceFailedException.class,
-              "NameNode still not leave safemode",
-              () -> miniCluster.transitionToObserver(0));
+          "NameNode still not leave safemode", 
+          () -> miniCluster.transitionToObserver(0));
     }
   }
 }

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

@@ -171,17 +171,17 @@ public void testObserverIllegalTransition() throws Exception {
   @Test
   public void testObserverTransitionInSafeMode() throws Exception {
     NameNodeAdapter.enterSafeMode(cluster.getNameNode(0), false);
-    DFSHAAdmin tool = new DFSHAAdmin();
-    tool.setConf(conf);
+    DFSHAAdmin admin = new DFSHAAdmin();
+    admin.setConf(conf);
     System.setIn(new ByteArrayInputStream("yes\n".getBytes()));
-    int result = tool.run(
-            new String[]{"-transitionToObserver", "-forcemanual", "nn1"});
+    int result = admin.run(
+        new String[]{"-transitionToObserver", "-forcemanual", "nn1"});
     assertEquals("State transition returned: " + result, -1, result);
 
     NameNodeAdapter.leaveSafeMode(cluster.getNameNode(0));
     System.setIn(new ByteArrayInputStream("yes\n".getBytes()));
-    int result1 = tool.run(
-            new String[]{"-transitionToObserver", "-forcemanual", "nn1"});
+    int result1 = admin.run(
+        new String[]{"-transitionToObserver", "-forcemanual", "nn1"});
     assertEquals("State transition returned: " + result1, 0, result1);
     assertFalse(cluster.getNameNode(0).isInSafeMode());
   }