Nowadays, most of the systems are transforming data in the form of XML, JSON, etc, but legacy applications/systems are still using Flat files to exchange data between the systems.

A Flat File can contain multiple lines of data with each line containing different line identifiers. Each line can have many fields of data, separated by a special character like Comma, Pipe, and Fixed width.

How to Parse Multi-Segment Flat Files With MuleSoft?

If you are working with multiple types of records in the file to transform, then you'll need to use a structure definition that controls how these different records are combined in a file. To read a multi-segment flat file in Mule, Flat file schema will play a key role in it. Preparing flat file schema needs to follow certain rules, and Mule has some limitations.

Keywords in a Flat File Schema:

Group: Several segments are grouped together. A group segment can also include child segments.

Segment: Segment is a line of data that has any number of elements.

Element: Element is a data item, which is associated with datatype and value.

Structure: Structure requires identifying the segments, and the segments have unique identifier codes/tags to identify the data.

ID: Structure identifier.

Name: Structure name.

tagStart: Starting number for segment identifier and required parameter for flat file schema. MuleSoft supports only the value 0.

tagLength: Number of columns in segment identifier tags (all the segments should be the same in length).

Data: List of the segments and groups in the structure.

Flat File Schema:

form: FLATFILE
structures:
- id: 'MultiSegment'
  name: MultiSegment
  tagStart: 0
  tagLength: 7
  data:
  - groupId: 'Data'
    items:
    - groupId: 'Flightsdata'
      count: '>1'
      items:
        - { idRef: 'flight', count: 1 }
        - { idRef: 'Account', count: '>1' }
segments:
- id: 'flight'
  name: flight
  tag: 'flights'
  values:
  - { name: 'cid', type: String, length: 10 }
  - { name: 'airlineName', type: String, length: 15 }
  - { name: 'price', type: String, length: 15 }
  - { name: 'departureDate', type: String, length: 15 }
  - { name: 'planeType', type: String, length: 15 }
  - { name: 'origination', type: String, length: 15 }
  - { name: 'code', type: String, length: 15 }
  - { name: 'emptySeats', type: String, length: 15 }
  - { name: 'destination', type: String, length: 15 }
- id: 'Account'
  name: Account
  tag: 'Account'
  values:
  - { name: 'Billing_Street', type: String, length: 30 }
  - { name: 'Billing_City', type: String, length: 15 }
  - { name: 'Billing_Country', type: String, length: 15 }
  - { name: 'Billing_State', type: String, length: 13 }
  - { name: 'Name', type: String, length: 30 }
  - { name: 'BillingPostalCode', type: String, length: 15 }

By default, all the defined segments are mandatory. If you want to make it as an Optional, then use "Usage code" property.
Ex: { idRef: 'Accounts', usage: O }

Mule Flow:

Configuration XML:

<flow name="multi-segment-flatfileFlow">
<file:inbound-endpoint path="src/main/resources/Input" moveToDirectory="src/main/resources/Archive" responseTimeout="10000" doc:name="Read files from Input Directory"/>
<dw:transform-message doc:name="Transform Message" metadata:id="5b9b30a6-f75b-4b8b-b297-e35026bfaed8">
<dw:input-payload mimeType="text/plain">
<dw:reader-property name="schemaPath" value="Multi-structure-segment-schema.ffd"/>
<dw:reader-property name="structureIdent" value="MultiSegment"/>
</dw:input-payload>
<dw:set-payload><![CDATA[%dw 1.0
%output application/xml skipNullOn="everywhere"
---
{
flightsdata: {
flights: {
flight: {
cid: payload.Data.flight.cid,
airlineName: payload.Data.flight.airlineName,
price: payload.Data.flight.price,
departureDate: payload.Data.flight.departureDate,
planeType: payload.Data.flight.planeType,
origination: payload.Data.flight.origination,
code: payload.Data.flight.code,
emptySeats: payload.Data.flight.emptySeats,
destination: payload.Data.flight.destination
},
Accounts: {
(payload.Data.Account map ((account , indexOfAccount) -> {
Account: {
Billing_Street: account.Billing_Street,
Billing_City: account.Billing_City,
Billing_Country: account.Billing_Country,
Billing_State: account.Billing_State,
Name: account.Name,
BillingPostalCode: account.BillingPostalCode
}
}))
}
}
}
}]]></dw:set-payload>
</dw:transform-message>

<file:outbound-endpoint path="src/main/resources/Output" outputPattern="#[org.mule.util.StringUtils.substringBefore(message.inboundProperties.originalFilename, '.')+'.xml']" responseTimeout="10000" doc:name="Write File in Output Directory"/>
</flow>