我有一个简单的spark应用程序，我试图在yarn cluster上广播一个string类型的变量。但是每次我试图访问广播的ed变量值时，我都会在任务中得到null。如果你们能告诉我，我做错了什么，这真的很有帮助。我的代码是follows:-

public class TestApp implements Serializable { 
  static Broadcast<String[]> mongoConnectionString; 

  public static void main( String[] args ) { 
    String mongoBaseURL = args[0]; 
    SparkConf sparkConf =  new SparkConf().setAppName(Constants.appName); 
    JavaSparkContext javaSparkContext = new JavaSparkContext(sparkConf); 

    mongoConnectionString = javaSparkContext.broadcast(args); 

    JavaSQLContext javaSQLContext = new JavaSQLContext(javaSparkContext); 

    JavaSchemaRDD javaSchemaRDD = javaSQLContext.jsonFile(hdfsBaseURL+Constants.hdfsInputDirectoryPath); 

    if(javaSchemaRDD!=null) { 
      javaSchemaRDD.registerTempTable("LogAction"); 
      javaSchemaRDD.cache(); 
      pageSchemaRDD = javaSQLContext.sql(SqlConstants.getLogActionPage); 
      pageSchemaRDD.foreach(new Test());     
    } 
  } 

  private static class Test implements VoidFunction<Row> { 
    private static final long serialVersionUID = 1L; 

    public void call(Row t) throws Exception { 
      logger.info("mongoConnectionString "+mongoConnectionString.value()); 
    } 
  } 
}