Spark 学习（在master节点提供向外服务）

利用Spark进行数据的处理之后，需要将结果返回给客户端，一种办法就是将处理得结果保存起来，客户端去访问这个结果。这种模式比较适合计算量比较大，结果相对比较稳定，实时性不高的情况。另外一种办法就是直接在SparkContext提供服务给客户端，用JavaWeb进行是一种选项，这里采用利用Scala编程，对外提供http服务，返回的结果是Json格式，下面是代码：

import javax.servlet.http.{HttpServletRequest, HttpServletResponse}
import org.apache.tools.ant.taskdefs.Java
import org.mortbay.jetty.{HttpStatus, Request}
import org.mortbay.jetty.{HttpStatus, Request, Server}
import org.mortbay.jetty.handler._
import org.apache.spark.sql.hive._
import org.apache.spark.{SparkContext,SparkConf}

/**
  * Created by tsq on 2016-10-04.
  */
object MainThread extends AbstractHandler {

  var _server: Server = null

  override def handle(target: String,
                      request: HttpServletRequest,
                      response: HttpServletResponse,
                      dispatch: Int): Unit = {
    val url = request.getRequestURI
    url.substring(url.lastIndexOf("/") + 1, url.length) match {
      case "getData" => {
        response.setContentType("text/html;charset=utf-8")
        response.setStatus(HttpStatus.ORDINAL_200_OK)
        response.getWriter().println(getData(request))
        request.asInstanceOf[Request].setHandled(true)
        response.getWriter.close()

      }
      case "stop" => {
        response.setContentType("text/html;charset=utf-8")
        response.setStatus(HttpStatus.ORDINAL_200_OK)
        response.getWriter().println("已经关闭")
        request.asInstanceOf[Request].setHandled(true)
        response.getWriter.close()
        StopThreadEx()
      }
      case _ => {
        response.setStatus(HttpStatus.ORDINAL_404_Not_Found);
        request.asInstanceOf[Request].setHandled(true)
      }
    }
  }

  def StopThreadEx(): Unit = {
    var theRunable = new StopThread(_server)
    theRunable.start()
  }

  def getData(request: HttpServletRequest): String = {
    var theParams = request.getParameterMap
    var theRet = ""
    var theKeys = theParams.keySet().toArray()
    for (theKey <- theKeys) {
      theRet += "," + theKey + "=" + request.getParameter(theKey.toString)
    }
    "这是您要的数据:" + theRet
  }

  def main(args: Array[String]): Unit = {
    _server = new Server(9998)
    _server.setHandler(this)
    println("监控启动")
    _server.start()
  }

}

本质上还是利用Java在进行http服务，但这种方式下和Scala结合，会比较方便，适合实时性比较高的。

虽然有很多开源方案更为简单，但对于小规模应用，这种直接的方式有的时候也是不错的选择。