promote the speed of convert files to RDDS

Author: surongquan

streaming/src/main/scala/org/apache/spark/streaming/dstream/FileInputDStream.scala

@@ -27,6 +27,7 @@ import org.apache.spark.rdd.RDD
 import org.apache.spark.rdd.UnionRDD
 import org.apache.spark.streaming.{StreamingContext, Time}
 import org.apache.spark.util.TimeStampedHashMap
+import scala.collection.mutable.ArrayBuffer
 
 
 private[streaming]
@@ -120,14 +121,14 @@ class FileInputDStream[K: ClassTag, V: ClassTag, F <: NewInputFormat[K,V] : Clas
 
   /** Generate one RDD from an array of files */
   private def filesToRDD(files: Seq[String]): RDD[(K, V)] = {
-    val fileRDDs = files.map(file => context.sparkContext.newAPIHadoopFile[K, V, F](file))
-    files.zip(fileRDDs).foreach { case (file, rdd) => {
+    val fileRDDs = for (file <- files; rdd = context.sparkContext.newAPIHadoopFile[K, V, F](file)) yield {
       if (rdd.partitions.size == 0) {
         logError("File " + file + " has no data in it. Spark Streaming can only ingest " +
           "files that have been \"moved\" to the directory assigned to the file stream. " +
           "Refer to the streaming programming guide for more details.")
       }
-    }}
+      rdd
+    }
     new UnionRDD(context.sparkContext, fileRDDs)
   }