[MINOR][DOC] Fix style in examples across documentation

## What changes were proposed in this pull request?

This PR fixes the documentation as below:

  -  Python has 4 spaces and Java and Scala has 2 spaces (See https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Guide).

  - Avoid excessive parentheses and curly braces for anonymous functions. (See https://github.com/databricks/scala-style-guide#anonymous)

## How was this patch tested?

N/A

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #14593 from HyukjinKwon/minor-documentation.

1 files changed, 24 insertions, 24 deletions

diff --git a/docs/streaming-custom-receivers.md b/docs/streaming-custom-receivers.md
index 479140f519..fae5901e8d 100644
--- a/docs/streaming-custom-receivers.md
+++ b/docs/streaming-custom-receivers.md
@@ -59,8 +59,8 @@ class CustomReceiver(host: String, port: Int)
   }
 
   def onStop() {
-   // There is nothing much to do as the thread calling receive()
-   // is designed to stop by itself if isStopped() returns false
+    // There is nothing much to do as the thread calling receive()
+    // is designed to stop by itself if isStopped() returns false
   }
 
   /** Create a socket connection and receive data until receiver is stopped */
@@ -68,29 +68,29 @@ class CustomReceiver(host: String, port: Int)
     var socket: Socket = null
     var userInput: String = null
     try {
-     // Connect to host:port
-     socket = new Socket(host, port)
-
-     // Until stopped or connection broken continue reading
-     val reader = new BufferedReader(
-       new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8))
-     userInput = reader.readLine()
-     while(!isStopped && userInput != null) {
-       store(userInput)
-       userInput = reader.readLine()
-     }
-     reader.close()
-     socket.close()
-
-     // Restart in an attempt to connect again when server is active again
-     restart("Trying to connect again")
+      // Connect to host:port
+      socket = new Socket(host, port)
+
+      // Until stopped or connection broken continue reading
+      val reader = new BufferedReader(
+        new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8))
+      userInput = reader.readLine()
+      while(!isStopped && userInput != null) {
+        store(userInput)
+        userInput = reader.readLine()
+      }
+      reader.close()
+      socket.close()
+
+      // Restart in an attempt to connect again when server is active again
+      restart("Trying to connect again")
     } catch {
-     case e: java.net.ConnectException =>
-       // restart if could not connect to server
-       restart("Error connecting to " + host + ":" + port, e)
-     case t: Throwable =>
-       // restart if there is any other error
-       restart("Error receiving data", t)
+      case e: java.net.ConnectException =>
+        // restart if could not connect to server
+        restart("Error connecting to " + host + ":" + port, e)
+      case t: Throwable =>
+        // restart if there is any other error
+        restart("Error receiving data", t)
     }
   }
 }