How to Read HTTP Attachments in Mule 4

Prepare a PostMan test with 2 files to send to Mule application

Assuming mule app's listening on http://localhost:8081/test, below's the PostMan request:

Use dataweave to extract the attachments

• After the HTTP listener, put a dataweave to extract the attachment:

<http:listener doc:name="Listener" doc:id="62702d1c-a913-40bb-9b53-baef97099c65" config-ref="HTTP_Listener_config" path="/test"/>
<ee:transform doc:name="Transform Message" doc:id="3cdb42df-8c13-44c5-8575-9617c7842349" >
  <ee:message >
    <ee:set-payload ><![CDATA[%dw 2.0
output application/java
var payloadParts=payload pluck($) default []
---
payloadParts[0] pluck($) default []]]></ee:set-payload>
  </ee:message>
</ee:transform>

• the HTTP inbound payload is a map of only one entry "parts".
• The variable "payloadParts" is an array of parts(only 1 item) that are plucked from the HTTP inbound map payload. 
• the variable "payloadParts" is also a map, where keys are the HTTP form data keys, like "file1" and "file2" in this case, the values are the actual attachments.
• The dataweave script then plucks the attachments into an array, to be processed by the following steps.

Iterate through the attachments and write to file

<foreach doc:name="For Each" doc:id="77f6eeb0-6af3-4d4d-86c1-c71a17d6ba13">
  <logger level="INFO" doc:name="Logger" doc:id="ad801e73-c208-464f-9641-dbaa1b5191eb" message='#[payload.headers."Content-Disposition".filename]' />
    <file:write doc:name="Write" doc:id="7bab023a-d246-4afd-a60b-f348aaf52b3d" config-ref="File_Config" path='#[payload.headers."Content-Disposition".filename]'>
      <file:content><![CDATA[#[payload.content]]]></file:content>
    </file:write>
</foreach>

payload.headers."Content-Disposition".filename