我使用pyspark运行模型（jar文件），但遇到了这个问题。

ERROR:root:Exception while sending command.
    Traceback (most recent call last):
      File "/home/spark/python/lib/py4j-0.10.7-src.zip/py4j/java_gateway.py", line 1159, in send_command
        raise Py4JNetworkError("Answer from Java side is empty")
    py4j.protocol.Py4JNetworkError: Answer from Java side is empty

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/spark/python/lib/py4j-0.10.7-src.zip/py4j/java_gateway.py", line 985, in send_command
    response = connection.send_command(command)
  File "/home/spark/python/lib/py4j-0.10.7-src.zip/py4j/java_gateway.py", line 1164, in send_command
    "Error while receiving", e, proto.ERROR_ON_RECEIVE)
py4j.protocol.Py4JNetworkError: Error while receiving
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 39328)
Traceback (most recent call last):
  File "/opt/anaconda3/lib/python3.7/socketserver.py", line 316, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/opt/anaconda3/lib/python3.7/socketserver.py", line 347, in process_request
    self.finish_request(request, client_address)
  File "/opt/anaconda3/lib/python3.7/socketserver.py", line 360, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/opt/anaconda3/lib/python3.7/socketserver.py", line 720, in __init__
    self.handle()
  File "/home/spark/python/pyspark/accumulators.py", line 265, in handle
    poll(accum_updates)
  File "/home/spark/python/pyspark/accumulators.py", line 238, in poll
    if func():
  File "/home/spark/python/pyspark/accumulators.py", line 242, in accum_updates
    num_updates = read_int(self.rfile)
  File "/home/spark/python/pyspark/serializers.py", line 692, in read_int
    raise EOFError
EOFError
----------------------------------------
--------------------------------------------------------
Py4JError              Traceback (most recent call last)
<ipython-input-5-497c78df0390> in <module>
----> 1 model = train_model(trainDf,testDf)

<ipython-input-3-2658aebab70f> in train_model(trainDF, testDF)
     66     )
     67     pipeline = Pipeline(stages=[xgboost])
---> 68     model = pipeline.fit(trainDF)
     69 
     70     # model.transform(testDF)

/home/spark/python/pyspark/ml/base.py in fit(self, dataset, params)
    130                 return self.copy(params)._fit(dataset)
    131             else:
--> 132                 return self._fit(dataset)
    133         else:
    134             raise ValueError("Params must be either a param map or a list/tuple of param maps, "

/home/spark/python/pyspark/ml/pipeline.py in _fit(self, dataset)
    107                     dataset = stage.transform(dataset)
    108                 else:  # must be an Estimator
--> 109                     model = stage.fit(dataset)
    110                     transformers.append(model)
    111                     if i < indexOfLastEstimator:

/home/spark/python/pyspark/ml/base.py in fit(self, dataset, params)
    130                 return self.copy(params)._fit(dataset)
    131             else:
--> 132                 return self._fit(dataset)
    133         else:
    134             raise ValueError("Params must be either a param map or a list/tuple of param maps, "

/home/spark/python/pyspark/ml/wrapper.py in _fit(self, dataset)
    286 
    287     def _fit(self, dataset):
--> 288         java_model = self._fit_java(dataset)
    289         model = self._create_model(java_model)
    290         return self._copyValues(model)

/home/spark/python/pyspark/ml/wrapper.py in _fit_java(self, dataset)
    283         """
    284         self._transfer_params_to_java()
--> 285         return self._java_obj.fit(dataset._jdf)
    286 
    287     def _fit(self, dataset):

/home/spark/python/lib/py4j-0.10.7-src.zip/py4j/java_gateway.py in __call__(self, *args)
   1255         answer = self.gateway_client.send_command(command)
   1256         return_value = get_return_value(
-> 1257             answer, self.gateway_client, self.target_id, self.name)
   1258 
   1259         for temp_arg in temp_args:

/home/spark/python/pyspark/sql/utils.py in deco(*a,**kw)
     61     def deco(*a,**kw):
     62         try:
---> 63             return f(*a,**kw)
     64         except py4j.protocol.Py4JJavaError as e:
     65             s = e.java_exception.toString()

/home/spark/python/lib/py4j-0.10.7-src.zip/py4j/protocol.py in get_return_value(answer, gateway_client, target_id, name)
    334             raise Py4JError(
    335                 "An error occurred while calling {0}{1}{2}".
--> 336                 format(target_id, ".", name))
    337     else:
    338         type = answer[1]

Py4JError: An error occurred while calling o171.fit

我的密码是，

def train_model(trainDF,testDF):
    xgboost = XGBoostClassifier(
        featuresCol="features",
        labelCol="label",
        predictionCol="prediction",
        numClass=10,
        missing=0.0
    )
    pipeline = Pipeline(stages=[xgboost])
    model = pipeline.fit(trainDF)
    model.transform(testDF)
    return model