Use a Reader Property through a Connector Operation

Connector operations that read input data provide an outpuMimeType field that you can use to identify the input MIME type. This field also accepts one or more reader properties, which is useful for helping DataWeave read the input correctly.

By default, the DataWeave reader treats a comma (,) as a separator. However, assume that a CSV input is separated by the pipe (|) but that the content also contains commas. You can set a CSV reader property to recognize the pipe as the separator.

Pipe-separated CSV Input

id | name | role
1234 | Shokida,Mr. | dev
2345 | Achaval,Mr. | arch
3456 | Felisatti,Ms. | mngr
4567 | Chibana,Mr. | dev

Before you begin, note that 2.x versions of DataWeave are used by Mule 4 apps. For DataWeave in Mule 3 apps, refer to DataWeave version 1.2 examples. For other DataWeave versions, you can use the version selector in the DataWeave table of contents.

The following example uses the Read operation in the File connector to read the pipe-separated (|) CSV input, and it uses a DataWeave script in the Transform Message component to output a row of the input in comma-separated format.

Mule Flow:

<flow name="ex-use-csv-reader-props" >
	<scheduler doc:name="Scheduler" >
		<scheduling-strategy >
			<fixed-frequency frequency="90" timeUnit="SECONDS"/>
		</scheduling-strategy>
	</scheduler>
	<file:read doc:name="Read" config-ref="File_Config" path="staff.csv"
	           outputMimeType='application/csv; separator=|; header=true'/>
	<ee:transform doc:name="Transform Message" >
		<ee:message>
			<ee:set-payload><![CDATA[%dw 2.0
output application/csv header = false
---
payload[1]]]></ee:set-payload>
		</ee:message>
	</ee:transform>
	<logger level="INFO" doc:name="Logger" message="#[payload]"/>
</flow>

The Scheduler component (<scheduler/>) in the example generates a Mule event each time it triggers the flow.

The Read operation (<file:read/>) uses outputMimeType='application/csv; separator=|; header=true' to identify the input MIME type (application/csv), the CSV separator (|), and the header setting (true).

The script in the Transform Message component (<ee:transform-message/>) returns the second row from the input CSV (2345 , Achaval\,Mr. , arch). The script uses payload[1] to select that row because DataWeave treats each row in the CSV as an index of an array. The output is comma-separated because the default CSV separator is a comma. The script omits the CSV header from the output by using the output directive (output application/csv header = false).

The Logger component (<logger/>), which is set to payload, writes the comma-separated output as INFO in its LoggerMessageProcessor message: 2345 , Achaval\,Mr. , arch. To avoid treating the comma before "Mr." as a separator, the CSV output escapes the comma with a backslash (Achaval\,Mr.).

The following examples pass reader properties through the outputMimeType field:

CSV example that uses streaming=true; header=true
JSON example that uses streaming=true

Use a Reader Property through a Connector Operation

See Also