如何使用 ExecuteScript（以 python 作为脚本引擎）进行加数练习？ 【新手尝试学习NiFi】

Question

我对 NiFi 比较陌生，不确定如何正确执行以下操作。我想使用ExecuteScript 处理器（脚本引擎：python）执行以下操作（请仅在 python 中）：

1）有一个CSV文件包含以下信息（第一行是标题）：

first,second,third
1,4,9
7,5,2
3,8,7

2) 我想找到各个行的总和并生成一个带有修改后的标题的最终文件。最终文件应如下所示：

first,second,third,total
1,4,9,14
7,5,2,14
3,8,7,18

对于python脚本，我写了：

def summation(first,second,third):
    numbers = first + second + third
    return numbers
flowFile = session.get()
if (flowFile != None):
    flowFile = session.write(flowFile, summation())

但它不起作用，我不知道如何解决这个问题。谁能告诉我如何解决这个问题？

NiFi 流程：

谢谢

Answer 1

您的脚本没有按照您的意愿执行。有几种方法可以解决这个问题：

1. 使用迭代 CSV 内容中的行的脚本一次对整个流文件进行操作
2. 将 CSV 内容中的行视为“记录”，并使用处理单行的脚本对每条记录进行操作

我将对您的脚本进行更改，以便一次处理整个流程文件内容；您可以阅读有关Record* 处理器here、here 和here 的更多信息。

这是一个执行您期望的操作的脚本。请注意差异以查看我在哪里进行了更改（这个脚本当然可以变得更加高效和简洁；演示正在发生的事情很冗长，而且我不是 Python 专家）。

import json
from java.io import BufferedReader, InputStreamReader
from org.apache.nifi.processor.io import StreamCallback

# This PyStreamCallback class is what the processor will use to ingest and output the flowfile content
class PyStreamCallback(StreamCallback):
  def __init__(self):
        pass
  def process(self, inputStream, outputStream):
      try:
        # Get the provided inputStream into a format where you can read lines
        reader = BufferedReader(InputStreamReader(inputStream))
        # Set a marker for the first line to be the header
        isHeader = True        
        try:
          # A holding variable for the lines
          lines = []
          # Loop indefinitely
          while True:
            # Get the next line
            line = reader.readLine()
            # If there is no more content, break out of the loop
            if line is None:
              break
            # If this is the first line, add the new column
            if isHeader:
              header = line + ",total"
              # Write the header line and the new column
              lines.append(header)
              # Set the header flag to false now that it has been processed
              isHeader = False
            else:
              # Split the line (a string) into individual elements by the ',' delimiter
              elements = self.extract_elements(line)
              # Get the sum (this method is unnecessary but shows where your "summation" method would go)
              sum = self.summation(elements)
              # Write the output of this line
              newLine = ",".join([line, str(sum)])
              lines.append(newLine)

          # Now out of the loop, write the output to the outputStream
          output = "\n".join([str(l) for l in lines])
          outputStream.write(bytearray(output.encode('utf-8')))

        finally:
            if reader is not None:
                reader.close()

      except Exception as e:
        log.warn("Exception in Reader")
        log.warn('-' * 60)
        log.warn(str(e))
        log.warn('-' * 60)
        raise e
        session.transfer(flowFile, REL_FAILURE)

  def extract_elements(self, line):
    # This splits the line on the ',' delimiter and converts each element to an integer, and puts them in a list
    return [int(x) for x in line.split(',')]

  # This method replaces your "summation" method and can accept any number of inputs, not just 3
  def summation(self, list):
    # This returns the sum of all items in the list
    return sum(list)


flowFile = session.get()
if (flowFile != None):
  flowFile = session.write(flowFile,PyStreamCallback())
  session.transfer(flowFile, REL_SUCCESS)

我的流程的结果（使用您在 GenerateFlowFile 处理器中的输入）：

2018-07-20 13:54:06,772 INFO [Timer-Driven Process Thread-5] o.a.n.processors.standard.LogAttribute LogAttribute[id=b87f0c01-0164-1000-920e-799647cb9b48] logging for flow file StandardFlowFileRecord[uuid=de888571-2947-4ae1-b646-09e61c85538b,claim=StandardContentClaim [resourceClaim=StandardResourceClaim[id=1532106928567-1, container=default, section=1], offset=2499, length=51],offset=0,name=470063203212609,size=51]
--------------------------------------------------
Standard FlowFile Attributes
Key: 'entryDate'
    Value: 'Fri Jul 20 13:54:06 EDT 2018'
Key: 'lineageStartDate'
    Value: 'Fri Jul 20 13:54:06 EDT 2018'
Key: 'fileSize'
    Value: '51'
FlowFile Attribute Map Content
Key: 'filename'
    Value: '470063203212609'
Key: 'path'
    Value: './'
Key: 'uuid'
    Value: 'de888571-2947-4ae1-b646-09e61c85538b'
--------------------------------------------------
first,second,third,total
1,4,9,14
7,5,2,14
3,8,7,18