[ROCKETMQ-13] Wrong log level for AcceptSocketService termination.

Additionally, added code comments and did a cleanup.

JIRA issue: https://issues.apache.org/jira/browse/ROCKETMQ-13

rocketmq-store/src/main/java/com/alibaba/rocketmq/store/ha/HAService.java

@@ -46,7 +46,7 @@ public class HAService {
 
     private final AtomicInteger connectionCount = new AtomicInteger(0);
 
-    private final List<HAConnection> connectionList = new LinkedList<HAConnection>();
+    private final List<HAConnection> connectionList = new LinkedList<>();
 
     private final AcceptSocketService acceptSocketService;
 
@@ -170,17 +170,22 @@ public class HAService {
         return push2SlaveMaxOffset;
     }
 
+    /**
+     * Listens to slave connections to create {@link HAConnection}.
+     */
     class AcceptSocketService extends ServiceThread {
         private ServerSocketChannel serverSocketChannel;
         private Selector selector;
         private final SocketAddress socketAddressListen;
 
-
         public AcceptSocketService(final int port) {
             this.socketAddressListen = new InetSocketAddress(port);
         }
 
-
+        /**
+         * Starts listening to slave connections.
+         * @throws Exception If fails.
+         */
         public void beginAccept() throws Exception {
             this.serverSocketChannel = ServerSocketChannel.open();
             this.selector = RemotingUtil.openSelector();
@@ -190,6 +195,7 @@ public class HAService {
             this.serverSocketChannel.register(this.selector, SelectionKey.OP_ACCEPT);
         }
 
+        /** {@inheritDoc} */
         @Override
         public void shutdown(final boolean interrupt) {
             super.shutdown(interrupt);
@@ -202,6 +208,7 @@ public class HAService {
             }
         }
 
+        /** {@inheritDoc} */
         @Override
         public void run() {
             log.info(this.getServiceName() + " service started");
@@ -210,10 +217,12 @@ public class HAService {
                 try {
                     this.selector.select(1000);
                     Set<SelectionKey> selected = this.selector.selectedKeys();
+
                     if (selected != null) {
                         for (SelectionKey k : selected) {
                             if ((k.readyOps() & SelectionKey.OP_ACCEPT) != 0) {
                                 SocketChannel sc = ((ServerSocketChannel) k.channel()).accept();
+
                                 if (sc != null) {
                                     HAService.log.info("HAService receive new connection, "
                                             + sc.socket().getRemoteSocketAddress());
@@ -234,16 +243,15 @@ public class HAService {
 
                         selected.clear();
                     }
-
                 } catch (Exception e) {
                     log.error(this.getServiceName() + " service has exception.", e);
                 }
             }
 
-            log.error(this.getServiceName() + " service end");
+            log.info(this.getServiceName() + " service end");
         }
 
-
+        /** {@inheritDoc} */
         @Override
         public String getServiceName() {
             return AcceptSocketService.class.getSimpleName();
@@ -256,8 +264,8 @@ public class HAService {
     class GroupTransferService extends ServiceThread {
 
         private final WaitNotifyObject notifyTransferObject = new WaitNotifyObject();
-        private volatile List<GroupCommitRequest> requestsWrite = new ArrayList<GroupCommitRequest>();
-        private volatile List<GroupCommitRequest> requestsRead = new ArrayList<GroupCommitRequest>();
+        private volatile List<GroupCommitRequest> requestsWrite = new ArrayList<>();
+        private volatile List<GroupCommitRequest> requestsRead = new ArrayList<>();
 
 
         public void putRequest(final GroupCommitRequest request) {
@@ -333,7 +341,7 @@ public class HAService {
 
     class HAClient extends ServiceThread {
         private static final int READ_MAX_BUFFER_SIZE = 1024 * 1024 * 4;
-        private final AtomicReference<String> masterAddress = new AtomicReference<String>();
+        private final AtomicReference<String> masterAddress = new AtomicReference<>();
         private final ByteBuffer reportOffset = ByteBuffer.allocate(8);
         private SocketChannel socketChannel;
         private Selector selector;