原始碼中的設計模式之模板設計模式

該類的繼承如下：

父類SparkSubmitOptionParser

抽掉不必要的程式碼

class SparkSubmitOptionParser {


  protected final void parse(List<String> args) {
    Pattern eqSeparatedOpt = Pattern.compile("(--[^=]+)=(.+)");

    int idx = 0;
    for (idx = 0; idx < args.size(); idx++) {
      String arg =
 
 args.get(idx);
      String value = null;

      Matcher m = eqSeparatedOpt.matcher(arg);
      if (m.matches()) {
        arg = m.group(1);
        value = m.group(2);
      }

      // Look for options with a value.
      String name = findCliOption(arg, opts);
      if (name != null) {
        if (
 
value == null) {
          if (idx == args.size() - 1) {
            throw new IllegalArgumentException(
                String.format("Missing argument for option '%s'.", arg));
          }
          idx++;
          value = args.get(idx);
        }
        if (!handle(name, value)) {
          break
 
;
        }
        continue;
      }

      // Look for a switch.
      name = findCliOption(arg, switches);
      if (name != null) {
        if (!handle(name, null)) {
          break;
        }
        continue;
      }

      if (!handleUnknown(arg)) {
        break;
      }
    }

    if (idx < args.size()) {
      idx++;
    }
    handleExtraArgs(args.subList(idx, args.size()));
  }
  protected boolean handle(String opt, String value) {
    throw new UnsupportedOperationException();
  }
  protected boolean handleUnknown(String opt) {
    throw new UnsupportedOperationException();
  }
  protected void handleExtraArgs(List<String> extra) {
    throw new UnsupportedOperationException();
  }

  private String findCliOption(String name, String[][] available) {
    for (String[] candidates : available) {
      for (String candidate : candidates) {
        if (candidate.equals(name)) {
          return candidates[0];
        }
      }
    }
    return null;
  }
}

parse 方法就被final修飾了不許子類繼承與修改，其下的程式碼執行流程都是固定了，只留下了handle（），handleUnknown（），handleExtraArgs（）三個受保護的抽象方法供繼承它的子類實現。所以這個所謂的模板設計就是強調程式碼執行流程已經模板話，但具體執行的什麼樣的邏輯，就交給子類來實現細節。

繼承它的子類

private[spark] abstract class SparkSubmitArgumentsParser extends SparkSubmitOptionParser

實現抽象方法的子類

刪去不必要的方法與變數內容

private[deploy] class SparkSubmitArguments(args: Seq[String], env: Map[String, String] = sys.env)
  extends SparkSubmitArgumentsParser {
 
  // Set parameters from command line arguments
  try {
    parse(args.asJava)
  } catch {
    case e: IllegalArgumentException =>
      SparkSubmit.printErrorAndExit(e.getMessage())
  }
  /** Fill in values by parsing user options. */
  override protected def handle(opt: String, value: String): Boolean = {
    opt match {
      case NAME =>
        name = value

      case MASTER =>
        master = value

      case CLASS =>
        mainClass = value

      case DEPLOY_MODE =>
        if (value != "client" && value != "cluster") {
          SparkSubmit.printErrorAndExit("--deploy-mode must be either \"client\" or \"cluster\"")
        }
        deployMode = value

      case NUM_EXECUTORS =>
        numExecutors = value

      case TOTAL_EXECUTOR_CORES =>
        totalExecutorCores = value

      case EXECUTOR_CORES =>
        executorCores = value

      case EXECUTOR_MEMORY =>
        executorMemory = value

      case DRIVER_MEMORY =>
        driverMemory = value

      case DRIVER_CORES =>
        driverCores = value

      case DRIVER_CLASS_PATH =>
        driverExtraClassPath = value

      case DRIVER_JAVA_OPTIONS =>
        driverExtraJavaOptions = value

      case DRIVER_LIBRARY_PATH =>
        driverExtraLibraryPath = value

      case PROPERTIES_FILE =>
        propertiesFile = value

      case KILL_SUBMISSION =>
        submissionToKill = value
        if (action != null) {
          SparkSubmit.printErrorAndExit(s"Action cannot be both $action and $KILL.")
        }
        action = KILL

      case STATUS =>
        submissionToRequestStatusFor = value
        if (action != null) {
          SparkSubmit.printErrorAndExit(s"Action cannot be both $action and $REQUEST_STATUS.")
        }
        action = REQUEST_STATUS

      case SUPERVISE =>
        supervise = true

      case QUEUE =>
        queue = value

      case FILES =>
        files = Utils.resolveURIs(value)

      case PY_FILES =>
        pyFiles = Utils.resolveURIs(value)

      case ARCHIVES =>
        archives = Utils.resolveURIs(value)

      case JARS =>
        jars = Utils.resolveURIs(value)

      case PACKAGES =>
        packages = value

      case PACKAGES_EXCLUDE =>
        packagesExclusions = value

      case REPOSITORIES =>
        repositories = value

      case CONF =>
        val (confName, confValue) = SparkSubmit.parseSparkConfProperty(value)
        sparkProperties(confName) = confValue

      case PROXY_USER =>
        proxyUser = value

      case PRINCIPAL =>
        principal = value

      case KEYTAB =>
        keytab = value

      case HELP =>
        printUsageAndExit(0)

      case VERBOSE =>
        verbose = true

      case VERSION =>
        SparkSubmit.printVersionAndExit()

      case USAGE_ERROR =>
        printUsageAndExit(1)

      case _ =>
        throw new IllegalArgumentException(s"Unexpected argument '$opt'.")
    }
    true
  }

  /**
   * Handle unrecognized command line options.
   *
   * The first unrecognized option is treated as the "primary resource". Everything else is
   * treated as application arguments.
   */
  override protected def handleUnknown(opt: String): Boolean = {
    if (opt.startsWith("-")) {
      SparkSubmit.printErrorAndExit(s"Unrecognized option '$opt'.")
    }

    primaryResource =
      if (!SparkSubmit.isShell(opt) && !SparkSubmit.isInternal(opt)) {
        Utils.resolveURI(opt).toString
      } else {
        opt
      }
    isPython = SparkSubmit.isPython(opt)
    isR = SparkSubmit.isR(opt)
    false
  }

  override protected def handleExtraArgs(extra: JList[String]): Unit = {
    childArgs ++= extra.asScala
  }
}

子類呼叫來自繼承parse父類的方法就會執行到自己重寫的方法！~~。