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1：SparkStreaming虽然说已经支持了很多不同类型的数据来源。但是有时候可能我们的一些数据来源非常特殊 ，不是它天然默认支持的，这时候就要自定义Receiver。而自定义Receiver，一般都是基于网络的方式。因为你传数据的话，一般是从另外一个网络端口传过来，至于传的协议是另外一码事。
2：从本质上来说，SparkStreaming中的所有Receiver，都是自定义的Receiver。所以你要想自定义一个Receiver，最最简单的方式，你就是看下已有的Receiver怎么去实现。
具体步骤：http://spark.apache.org/docs/latest/streaming-custom-receivers.html
class CustomReceiver(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() }//开启线程调receiver()方法
}.start()
}
def onStop() {
// 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 */
private def receive() {
var socket: Socket = null
var userInput: String = null
try {
// Connect to host:port，Receiver的时候就连上Socket
socket = new Socket(host, port)
// Until stopped or connection broken continue reading
val reader = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"))
userInput = reader.readLine()
while(!isStopped && userInput != null) {
store(userInput)
userInput = reader.readLine()//每读一行，存一次，一直循环
}
reader.close()
socket.close()
// Restart in an attempt to connect again when server is active again
restart("Trying to connect again")//先stop，然后再start()
} 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)
}
}
}// Assuming ssc is the StreamingContext
val customReceiverStream = ssc.receiverStream(new CustomReceiver(host, port))
val words = lines.flatMap(_.split(" "))
...