Why did not my custom Receiver get the right output? - spark-streaming

Question

I have a question about custom receiver of spark streaming.
I code a copy like the following :
import java.io.{BufferedReader, InputStreamReader}
import java.net.Socket
import java.nio.charset.StandardCharsets
import org.apache.spark.SparkConf
import org.apache.spark.Logging
import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.{Seconds, StreamingContext}
import org.apache.spark.streaming.receiver.Receiver
/**
* Custom Receiver that receives data over a socket. Received bytes is interpreted as
* text and \n delimited lines are considered as records. They are then counted and printed.
*
* To run this on your local machine, you need to first run a Netcat server
* `$ nc -lk 9999`
* and then run the example
* `$ bin/run-example org.apache.spark.examples.streaming.CustomReceiver localhost 9999`
*/
object CustomReceiver2 {
def main(args: Array[String]) {
// Create the context with a 1 second batch size
val sparkConf = new SparkConf().setAppName("CustomReceiver")
val ssc = new StreamingContext(sparkConf, Seconds(1))
// Create a input stream with the custom receiver on target ip:port and count the
// words in input stream of \n delimited text (eg. generated by 'nc')
val lines = ssc.receiverStream(new CustomReceiver2("192.168.1.0", 11.toInt))
lines.saveAsObjectFiles("hdfs:/tmp/customreceiver/")
ssc.start()
ssc.awaitTermination()
}
}
class CustomReceiver2(host: String, port: Int)
extends Receiver[String](StorageLevel.MEMORY_AND_DISK_2) with Logging {
def onStart() {
// Start the thread that receives data over a connection
new Thread("Socket Receiver") {
override def run() { receive() }
}.start()
}
def onStop() {
}
/** Create a socket connection and receive data until receiver is stopped */
private def receive() {
var socket: Socket = null
var userInput: String = null
try {
logInfo("Connecting to " + host + ":" + port)
socket = new Socket(host, port)
logInfo("Connected to " + host + ":" + port)
val reader = new BufferedReader(
new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8))
userInput = reader.readLine()
while(!isStopped && userInput != null) {
println("userInput= "+userInput)
store(userInput)
userInput = reader.readLine()
println("==store data finished==")
}
reader.close()
socket.close()
logInfo("Stopped receiving")
restart("Trying to connect again")
} catch {
case e: java.net.ConnectException =>
restart("Error connecting to " + host + ":" + port, e)
case t: Throwable =>
restart("Error receiving data", t)
}
}
}
It passes the compiler and runs smoothly. I did not take the output as i expected, because the hdfs file was empty all the time.
Could anyone give me a hand ?