SparkSubmit

-- main

	-- doSubmit
	
		// 解析参数
		-- parseArguments
		
			// master => --master => yarn
			// mainClass => --class => SparkPi(WordCount)
			-- parse
			
		-- submit
		
			-- doRunMain
			
			-- runMain
			
				// (childArgs, childClasspath, sparkConf, childMainClass)
				// 【Cluster】childMainClass => org.apache.spark.deploy.yarn.YarnClusterApplication
				// 【Client 】childMainClass => SparkPi(WordCount)
				-- prepareSubmitEnvironment
				
				// Class.forName("xxxxxxx")
				-- mainClass : Class = Utils.classForName(childMainClass)
				
				// classOf[SparkApplication].isAssignableFrom(mainClass)
				-- 【Cluster】a). mainClass.getConstructor().newInstance().asInstanceOf[SparkApplication]
				-- 【Client 】b). new JavaMainApplication(mainClass)
				
				-- app.start