flink源码学习之选择创建哪种类型的客户端

public static void main(final String[] args) {
  ... ...
  final List<CustomCommandLine> customCommandLines = loadCustomCommandLines(
      configuration,
      configurationDirectory);
  ... ...
  final CliFrontend cli = new CliFrontend(
        configuration,
        customCommandLines);
  ... ...
}

这里依次添加了 Generic、Yarn和Default三种命令行客户端（后面根据isActive()按顺序选择）：

public static List<CustomCommandLine> loadCustomCommandLines(Configuration configuration, String configurationDirectory) {
  List<CustomCommandLine> customCommandLines = new ArrayList<>();
  customCommandLines.add(new GenericCLI(configuration, configurationDirectory));

  //  Command line interface of the YARN session, with a special initialization here
  //  to prefix all options with y/yarn.
  final String flinkYarnSessionCLI = "org.apache.flink.yarn.cli.FlinkYarnSessionCli";
  try {
    customCommandLines.add(
      loadCustomCommandLine(flinkYarnSessionCLI,
        configuration,
        configurationDirectory,
        "y",
        "yarn"));
  } catch (NoClassDefFoundError | Exception e) {
    final String errorYarnSessionCLI = "org.apache.flink.yarn.cli.FallbackYarnSessionCli";
    try {
      LOG.info("Loading FallbackYarnSessionCli");
      customCommandLines.add(
          loadCustomCommandLine(errorYarnSessionCLI, configuration));
    } catch (Exception exception) {
      LOG.warn("Could not load CLI class {}.", flinkYarnSessionCLI, e);
    }
  }

  //  Tips: DefaultCLI must be added at last, because getActiveCustomCommandLine(..) will get the
  //        active CustomCommandLine in order and DefaultCLI isActive always return true.
  customCommandLines.add(new DefaultCLI(configuration));

  return customCommandLines;
}

在run()里面，进行客户端的选择：

protected void run(String[] args) throws Exception {
  ... ...
  final CustomCommandLine activeCommandLine =
        validateAndGetActiveCommandLine(checkNotNull(commandLine));
... ...
}

public CustomCommandLine validateAndGetActiveCommandLine(CommandLine commandLine) {
... ...
  for (CustomCommandLine cli : customCommandLines) {
  ... ...
  //在FlinkYarnSessionCli为active时优先返回FlinkYarnSessionCli。
    //对于DefaultCli，它的isActive方法总是返回true。
    if (cli.isActive(commandLine)) {
      return cli;
    }
  }
... ...
}

FlinkYarnSessionCli.java => Yarn客户端isActive的判断逻辑：

public boolean isActive(CommandLine commandLine) {
  final String jobManagerOption = commandLine.getOptionValue(addressOption.getOpt(), null);
  // 是否指定为per-job模式，即指定”-m yarn-cluster”; ID = "yarn-cluster"
  final boolean yarnJobManager = ID.equals(jobManagerOption);
  // 是否存在flink在yarn的appID，即yarn-session模式是否启动
  final boolean hasYarnAppId = commandLine.hasOption(applicationId.getOpt())
      || configuration.getOptional(YarnConfigOptions.APPLICATION_ID).isPresent();
  // executor的名字为 "yarn-session" 或 "yarn-per-job"
  final boolean hasYarnExecutor = YarnSessionClusterExecutor.NAME.equals(configuration.get(DeploymentOptions.TARGET))
      || YarnJobClusterExecutor.NAME.equals(configuration.get(DeploymentOptions.TARGET));
  //
  return hasYarnExecutor || yarnJobManager || hasYarnAppId || (isYarnPropertiesFileMode(commandLine) && yarnApplicationIdFromYarnProperties != null);
}