spark streaming動態修改廣播變量

在 foreach rdd中執行，重新廣播。可以基於job 批次數量 或者是 時間 
public class BroadcastStringPeriodicUpdater {
  private static final int PERIOD = 60 * 1000;
  private static volatile BroadcastStringPeriodicUpdater instance;

  private Broadcast<String> broadcast;
  private long lastUpdate = 0L;

  private BroadcastStringPeriodicUpdater() {}

  public static BroadcastStringPeriodicUpdater getInstance() {
    if (instance == null) {
      synchronized (BroadcastStringPeriodicUpdater.class) {
        if (instance == null) {
          instance = new BroadcastStringPeriodicUpdater();
        }
      }
    }
    return instance;
  }

  public String updateAndGet(SparkContext sc) {
    long now = System.currentTimeMillis();
    long offset = now - lastUpdate;
    if (offset > PERIOD || broadcast == null) {
      if (broadcast != null) {
        broadcast.unpersist();
      }
      lastUpdate = now;
      String value = fetchBroadcastValue();
      broadcast = JavaSparkContext.fromSparkContext(sc).broadcast(value);
    }
    return broadcast.getValue();
  }

  private String fetchBroadcastValue() {

  }
}

用的時候就可以這樣用

String broadcastValue = BroadcastStringPeriodicUpdater.getInstance().updateAndGet(rdd.context());