Parquet文件可选字段不存在

我对处理Parquet文件是个新手，我想开发一个mapreduce作业，用以下shcema读取许多输入Parquet文件：

{
  optional int96 dropoff_datetime;
  optional float dropoff_latitude;
  optional float dropoff_longitude;
  optional int32 dropoff_taxizone_id;
  optional float ehail_fee;
  optional float extra;
  optional float fare_amount;
  optional float improvement_surcharge;
  optional float mta_tax;
  optional int32 passenger_count;
  optional binary payment_type (UTF8);
  optional int96 pickup_datetime;
  optional float pickup_latitude;
  optional float pickup_longitude;
  optional int32 pickup_taxizone_id;
  optional int32 rate_code_id;
  optional binary store_and_fwd_flag (UTF8);
  optional float tip_amount;
  optional float tolls_amount;
  optional float total_amount;
  optional float trip_distance;
  optional binary trip_type (UTF8);
  optional binary vendor_id (UTF8);
  required int64 trip_id;
}

我工作的目的是计算每天每小时的平均旅行速度，所以我需要提取所有的旅行距离和上下车时间来计算持续时间，然后计算速度，但是当我在野外工作时会出现错误 trip_distance 不存在：这里是堆栈跟踪的一部分：

18/02/28 03:19:01 INFO mapreduce.Job:  map 2% reduce 0%
18/02/28 03:19:10 INFO mapreduce.Job: Task Id : attempt_1519722054260_0016_m_000011_2, Status : FAILED
Error: java.lang.RuntimeException: not found 20(trip_distance) element number 0 in group:
dropoff_datetime: Int96Value{Binary{12 constant bytes, [0, 0, 0, 0, 0, 0, 0, 0, -116, 61, 37, 0]}}
payment_type: ""
pickup_datetime: Int96Value{Binary{12 constant bytes, [0, 120, 66, 9, 78, 72, 0, 0, 3, 125, 37, 0]}}
pickup_latitude: 40.7565
pickup_longitude: -73.9781
pickup_taxizone_id: 161
store_and_fwd_flag: ""
trip_type: "uber"
vendor_id: ""
trip_id: 4776003633207

    at org.apache.parquet.example.data.simple.SimpleGroup.getValue(SimpleGroup.java:97)
    at org.apache.parquet.example.data.simple.SimpleGroup.getValueToString(SimpleGroup.java:119)
    at ParquetAssignmentSpeedAverageHours$ParquetMap.map(ParquetAssignmentSpeedAverageHours.java:48)
    at ParquetAssignmentSpeedAverageHours$ParquetMap.map(ParquetAssignmentSpeedAverageHours.java:37)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:146)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:787)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:170)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1866)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:164)

这是我的mapper类：

public static class ParquetMap extends Mapper<Text, Group, IntWritable, DoubleWritable> {
    private DoubleWritable one = new DoubleWritable(1);
    private IntWritable time = new IntWritable();
    private DoubleWritable result = new DoubleWritable();
    @Override
    public void map(Text key, Group value, Context context) throws IOException, InterruptedException {
        double duration;
        double distance;
        double speed;
        Binary pickupTimestamp = value.getInt96("pickup_datetime", 0);
        Binary dropoffTimestamp = value.getInt96("dropoff_datetime", 0);
        if (value.getValueToString(20, 0) != null) { //the trip_distance field
            distance = value.getFloat("trip_distance", 0);
        } else {
            distance = 0;
        }
        try {
            if (!pickupTimestamp.equals(dropoffTimestamp)) {
                duration = ((double)(getTimestampMillis(dropoffTimestamp) - getTimestampMillis(pickupTimestamp))/3600000);
                speed = (float) (distance / duration);
                result.set((speed));
                Calendar cal = Calendar.getInstance();
                cal.setTimeInMillis(getTimestampMillis(pickupTimestamp));
                time.set(cal.get(Calendar.HOUR_OF_DAY));
                context.write(time, result);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

有人能帮忙吗？谢谢，

这是运行时异常 java.lang.RuntimeException ; 这基本上表明代码有缺陷。
这个 public String getValueToString(int fieldIndex, int index) 方法内部调用 getValue(int fieldIndex, int index) 方法。实施 getValue(...) 如下所示

private Object getValue(int fieldIndex, int index) {
    List<Object> list;
    try {
      list = data[fieldIndex];
    } catch (IndexOutOfBoundsException e) {
      throw new RuntimeException("not found " + fieldIndex + "(" + schema.getFieldName(fieldIndex) + ") in group:\n" + this);
    }
    try {
      return list.get(index);
    } catch (IndexOutOfBoundsException e) {
      throw new RuntimeException("not found " + fieldIndex + "(" + schema.getFieldName(fieldIndex) + ") element number " + index + " in group:\n" + this);
    }
  }

这里，如果 fieldIndex 或者 index 不存在它抛出 IndexOutOfBoundsException ，重新抛出为 RuntimeException .
我的建议是 getValueToString(...) 必须直接检查字段的存在性。
由于数据集中的所有字段都是可选的，因此使用固定的 fieldIndex 不可靠。在这种情况下，只要假设它存在，让它失败 try-catch 块以检测缺勤情况，然后设置默认值：

try{
    distance = value.getFloat("trip_distance", 0);
}catch(RuntimeException e){
      distance = 0;
}

Parquet文件可选字段不存在

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