AWS - Mapping Template in API Gateway with VTL

Use Case:

When API Gateway integrates with AWS Service (like SQS) and need to transform data by using Request & Response Template.

AWS Console:

Go to the menu 'Resources' of an API in the service 'API Gateway'
Select a method. Click to the link 'Integration Request'
Go to Mapping Templates section, click a content type in the list of Content-Type. You will see the section of Request Template.

Notes:

AWS API Gateway only supports some functions (VTL tools), not fully support like AppSync.
- Function $utils in API Gateway: https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html
- Function $utils in AppSync: https://docs.aws.amazon.com/appsync/latest/devguide/utility-helpers-in-util.html
Using $input.path( ) to get Object instead of $input.json( ).

For example, API gateway integrates with SQS:

requestTemplates:
  application/json: |-
    Action=SendMessage&MessageBody={"field1":$util.urlEncode($input.json('$.field1'))}

Tricks:

## Convert String to Integer
#set($Val=0)
$Val.parseInt('123')
## Convert String to Long
#set($Val=100000000000000)
$Val.parseLong('123')

LInk Reference: https://aws.amazon.com/blogs/compute/using-api-gateway-mapping-templates-to-handle-changes-in-your-back-end-apis/

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