API Gateway mapping template : Convert form-data(POST) request to JSON

Question

I am sending some form-data in request body from postman. In aws API Gateway I have set Content-type as "multipart/form-data" and mapping template is following:

    #set($allParams = $input.params())
{
"body-json" : $input.json('$'),
"params" : {
#foreach($type in $allParams.keySet())
    #set($params = $allParams.get($type))
"$type" : {
    #foreach($paramName in $params.keySet())
    "$paramName" : "$util.escapeJavaScript($params.get($paramName))"
        #if($foreach.hasNext),#end
    #end
}
    #if($foreach.hasNext),#end
#end
},
"stage-variables" : {
#foreach($key in $stageVariables.keySet())
"$key" : "$util.escapeJavaScript($stageVariables.get($key))"
    #if($foreach.hasNext),#end
#end
},
"context" : {
    "account-id" : "$context.identity.accountId",
    "api-id" : "$context.apiId",
    "api-key" : "$context.identity.apiKey",
    "authorizer-principal-id" : "$context.authorizer.principalId",
    "caller" : "$context.identity.caller",
    "cognito-authentication-provider" : "$context.identity.cognitoAuthenticationProvider",
    "cognito-authentication-type" : "$context.identity.cognitoAuthenticationType",
    "cognito-identity-id" : "$context.identity.cognitoIdentityId",
    "cognito-identity-pool-id" : "$context.identity.cognitoIdentityPoolId",
    "http-method" : "$context.httpMethod",
    "stage" : "$context.stage",
    "source-ip" : "$context.identity.sourceIp",
    "user" : "$context.identity.user",
    "user-agent" : "$context.identity.userAgent",
    "user-arn" : "$context.identity.userArn",
    "request-id" : "$context.requestId",
    "resource-id" : "$context.resourceId",
    "resource-path" : "$context.resourcePath"
    }
}

However when I am getting the request on my lambda function everything is properly mapped into JSON, except my request body. Request body is coming as String. Following is the complete request:

  {
    "context": {
        "authorizer-principal-id": "",
        "cognito-authentication-type": "",
        "cognito-identity-id": "",
        "resource-path": "/env/Response",
        "account-id": "",
        "cognito-identity-pool-id": "",
        "request-id": "cd2052-11e7-92b6-e3c7d7dgh01",
        "api-id": "39dhjsr8",
        "resource-id": "skdsk5",
        "user-arn": "",
        "caller": "",
        "http-method": "POST",
        "cognito-authentication-provider": "",
        "api-key": "",
        "user": "",
    },
    "body-json": "------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"sig\"\r\n\r\nmcHeelgDQcYnjh5L2L92H8KLLE=\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"resultdescription\"\r\n\r\ncancelled.\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"result\"\r\n\r\nF\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"errorcode\"\r\n\r\n101\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"id\"\r\n\r\n420LU2UEG\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"key\"\r\n\r\ntdx\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"refid\"\r\n\r\n10480\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"name\"\r\n\r\nTest\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"date\"\r\n\r\n2016-02-28T20:05:05.6330000Z\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx\r\nContent-Disposition: form-data; name=\"timestamp\"\r\n\r\n2016-02-29T04:15:47.4797Z\r\n------WebKitFormBoundaryLAn6jCAA10bF7ZMx--",
    "params": {
        "path": {},
        "querystring": {},
        "header": {
           },
    "stage-variables": {}
}

I have 2 queries regarding this:

Is there any way where I can convert request body into JSON Object in API gateway mapping template itself?(Means instead of String, Request Body should come as JSON Object).
Or I have to convert request body String into JSON Object at lambda handler in my java code?

Any help will be highly appreciated, as I am new to AWS.

This is one reason I try to avoid API Gateway Mapping templates. Using Lamda-Proxy integration is so much easier. — Noel Llevares
Maybe this can help: stackoverflow.com/questions/41756190/… — Noel Llevares
Thanks but this I have read earlier and I am not getting any solution out of this. — Pallavi Kaushik

Noel Llevares Noel Llevares · Accepted Answer · 2017-11-07T10:48:13

It would be best if you send your payload as application/json. That way, you can have it parsed in the mapping template using $util.parseJson() and the request body will come out as an object.

If you want to stick with form-data, you'll have to convert it inside your handler.

In Node.js, I use querystring module for this. Not sure what you can use in Java.

API Gateway mapping template : Convert form-data(POST) request to JSON

2 Answers