Your first complete Spark application (using Scala and sbt)

== Your first Spark application (using Scala and sbt)

This page gives you the exact steps to develop and run a complete Spark application using http://www.scala-lang.org/[Scala] programming language and http://www.scala-sbt.org/[sbt] as the build tool.

[TIP] Refer to Quick Start's http://people.apache.org/~pwendell/spark-nightly/spark-master-docs/latest/quick-start.html#self-contained-applications[Self-Contained Applications] in the official documentation.

The sample application called SparkMe App is...FIXME

=== Overview

You're going to use http://www.scala-sbt.org/[sbt] as the project build tool. It uses build.sbt for the project's description as well as the dependencies, i.e. the version of Apache Spark and others.

The application's main code is under src/main/scala directory, in SparkMeApp.scala file.

With the files in a directory, executing sbt package results in a package that can be deployed onto a Spark cluster using spark-submit.

In this example, you're going to use Spark's local/spark-local.md[local mode].

=== Project's build - build.sbt

Any Scala project managed by sbt uses build.sbt as the central place for configuration, including project dependencies denoted as libraryDependencies.

build.sbt 

name         := "SparkMe Project"
version      := "1.0"
organization := "pl.japila"

scalaVersion := "2.11.7"

libraryDependencies += "org.apache.spark" %% "spark-core" % "1.6.0-SNAPSHOT"  // <1>
resolvers += Resolver.mavenLocal
<1> Use the development version of Spark 1.6.0-SNAPSHOT

=== SparkMe Application

The application uses a single command-line parameter (as args(0)) that is the file to process. The file is read and the number of lines printed out.

package pl.japila.spark

import org.apache.spark.{SparkContext, SparkConf}

object SparkMeApp {
  def main(args: Array[String]) {
    val conf = new SparkConf().setAppName("SparkMe Application")
    val sc = new SparkContext(conf)

    val fileName = args(0)
    val lines = sc.textFile(fileName).cache

    val c = lines.count
    println(s"There are $c lines in $fileName")
  }
}

=== sbt version - project/build.properties

sbt (launcher) uses project/build.properties file to set (the real) sbt up

sbt.version=0.13.9

TIP: With the file the build is more predictable as the version of sbt doesn't depend on the sbt launcher.

=== Packaging Application

Execute sbt package to package the application.

➜  sparkme-app  sbt package
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[info] Loading project definition from /Users/jacek/dev/sandbox/sparkme-app/project
[info] Set current project to SparkMe Project (in build file:/Users/jacek/dev/sandbox/sparkme-app/)
[info] Compiling 1 Scala source to /Users/jacek/dev/sandbox/sparkme-app/target/scala-2.11/classes...
[info] Packaging /Users/jacek/dev/sandbox/sparkme-app/target/scala-2.11/sparkme-project_2.11-1.0.jar ...
[info] Done packaging.
[success] Total time: 3 s, completed Sep 23, 2015 12:47:52 AM

The application uses only classes that comes with Spark so package is enough.

In target/scala-2.11/sparkme-project_2.11-1.0.jar there is the final application ready for deployment.

=== Submitting Application to Spark (local)

NOTE: The application is going to be deployed to local[*]. Change it to whatever cluster you have available (refer to spark-cluster.md[Running Spark in cluster]).

spark-submit the SparkMe application and specify the file to process (as it is the only and required input parameter to the application), e.g. build.sbt of the project.

NOTE: build.sbt is sbt's build definition and is only used as an input file for demonstration purposes. Any file is going to work fine.

➜  sparkme-app  ~/dev/oss/spark/bin/spark-submit --master "local[*]" --class pl.japila.spark.SparkMeApp target/scala-2.11/sparkme-project_2.11-1.0.jar build.sbt
Using Spark's repl log4j profile: org/apache/spark/log4j-defaults-repl.properties
To adjust logging level use sc.setLogLevel("INFO")
15/09/23 01:06:02 WARN NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
15/09/23 01:06:04 WARN MetricsSystem: Using default name DAGScheduler for source because spark.app.id is not set.
There are 8 lines in build.sbt

NOTE: Disregard the two above WARN log messages.

You're done. Sincere congratulations!

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