本期内容：
1. Spark Streaming的Transformation、Action源码图解
2. Spark Streaming的Input、Output源码图解
StreamingContext成员：socketStream
/**
* Create a input stream from TCP source hostname:port. Data is received using
* a TCP socket and the receive bytes it interepreted as object using the given
* converter.
* @param hostname Hostname to connect to for receiving data
* @param port Port to connect to for receiving data
* @param converter Function to convert the byte stream to objects
* @param storageLevel Storage level to use for storing the received objects
* @tparam T Type of the objects received (after converting bytes to objects)
*/
def socketStream[T: ClassTag](
hostname: String,
port: Int,
converter: (InputStream) => Iterator[T],
storageLevel: StorageLevel
): ReceiverInputDStream[T] = {
new SocketInputDStream[T](this, hostname, port, converter, storageLevel)
}
SocketInputDStream：
class SocketInputDStream[T: ClassTag](
ssc_ : StreamingContext,
host: String,
port: Int,
bytesToObjects: InputStream => Iterator[T],
storageLevel: StorageLevel
) extends ReceiverInputDStream[T](ssc_) {
def getReceiver(): Receiver[T] = {
new SocketReceiver(host, port, bytesToObjects, storageLevel)
}
}
ReceiverInputDStream：
abstract class ReceiverInputDStream[T: ClassTag](ssc_ : StreamingContext)
extends InputDStream[T](ssc_) {
...
InputDStream：
ssc.graph.addInputStream(this)
把ImputDStream放入到了graph中。
DStream.foreachRDD产生ForEachDStream对象，该对象通过register对象也放入了graph中。