Creating Web APIs (2024)

The capabilities described on this page are included in Appian's standard capability tier. Usage limits may apply.

Overview

This page illustrates the basic steps involved with creating web APIs along with examples of a GET & POST request to a web API.

To learn about web APIs and their configuration options, see Web APIs.
For a real-world example of how to build and test web APIs in Appian, see the Web API Tutorial.
To learn about web API authentication, see Web API Authentication.

Creating a web API

Appian makes it easy to create your web APIs by providing you with a series of templates to help you get started.

Selecting one of the templates will populate your web API with an example expression and test inputs, and convert it to use the proper HTTP method for that expression. If you already have your web API expression in mind, you can also create a web API from scratch.

Create a web API using a template

To create a web API using a template:

In your application, go to the Build view.
Click NEW > Web API.
In the Create Web API dialog, choose Select a template and select from one of the available templates.

Configure the following properties. Depending on your selected template, you may have more properties available than what is listed below.

Property	Description
Template	The name of the selected template.
Name	The name of your web API. This name is only visible to Appian developers.
Description	A short description about your web API.
HTTP Method	The HTTP method for your selected template.
Endpoint	The endpoint for the web API. This is used as part of the web API's URL to identify it and will be seen by end users and in log files for network devices and servers.

Create a web API from scratch

To create a web API from scratch:

In your application, go to the Build view.
Click NEW > Web API.
In the Create Web API dialog, choose Create from scratch.

Configure the following properties:

Property	Description
Name	The name of your web API. This name is only visible to Appian developers.
Description	A short description about your web API.
HTTP Method	The HTTP method for your web API. Options include: `GET`, `POST`, `PUT`, `DELETE`, and `PATCH`.
Endpoint	The endpoint for the web API. This is used as part of the web API's URL to identify it and will be seen by end users and in log files for network devices and servers.

Click CREATE.
In the Review Web API Security dialog, configure the security role map for the web API.
Click SAVE. The blank web API opens in a new tab or window.

Executing a smart service

Web APIs that use the POST, PUT, DELETE, or PATCH HTTP methods are able to execute a smart service.

Every smart service that can run inside a web API has an onSuccess and an onFailure parameter that expects an HTTP response defined using a!httpResponse():

When the smart service executes successfully, the HTTP response defined in the onSuccess parameter is returned.
When the smart service encounters an error and is unable to execute, the HTTP response defined in the onError parameter is returned.

The example below uses the Write to Data Store Entity smart service. When the write is successful, the web API results in an HTTP response with a 200 status code and a body containing the JSON-encoded data that was written to the data store.

When the write is unsuccessful, the web API results in an HTTP response with a status code of 500 and a body containing a JSON-encoded error message.

1234567891011121314151617181920212223242526272829 a!writeToDataStoreEntity( dataStoreEntity: cons!EMPLOYEE_ENTITY, valueToStore: type!Employee( firstName: http!request.queryParameters.firstName, lastName: http!request.queryParameters.laseName, department: http!request.queryParameters.department, title: http!request.queryParameters.title ), onSuccess: a!httpResponse( statusCode: 200, headers: { a!httpHeader(name: "Content-Type", value: "application/json") }, body: a!toJson( fv!storedValues ) ), onError: a!httpResponse( statusCode: 500, headers: { a!httpHeader(name: "Content-Type", value: "application/json") }, body: a!toJson( { error: "There was an error writing to the data store" } ) ))

Accessing the HTTP request

Data from the incoming HTTP request is exposed to the expression in the variable http!request.

This variable is a dictionary that contains the following fields:

Field	Type	Description
url	Text	The URL of the incoming request, including protocol, hostname, port, path, and query parameters
pathSegments	Variant (List of Text)	A list of text where each item in the list corresponds to a segment of the URL from the incoming request separated by forward slashes: `/`. The first item in the list will be the section of the URL that immediately follows the endpoint. Because this list is wrapped in a Variant, `count(http!request.pathSegments)` will always return 1. To get around this, designers can cast the field to a List of Text: `count(cast(typeof({""}),http!request.pathSegments))`. Indexing into pathSegments on the other hand, still works as it would for any list: `index(http!request.pathSegments, 1, null)`.
queryParameters	Dictionary	A dictionary where the keys are the names of the query parameters from the request and the values are the values of those parameters
headers	Dictionary	A dictionary where the keys are the names of the headers from the request and the values are the values of those headers. HTTP headers which contain sensitive information are not included in the dictionary. This includes headers with keys like `Authorization` or `Appian-API-Key`.
body	Text	The body of the incoming request
formData	Dictionary	An alternate representation of the request body that is a dictionary where the keys are the names of the fields from the body of the request and the values are the values of those fields. This is only available when the incoming request contains a `Content-Type` header with a value of `application/x-www-form-urlencoded` and the contents of the request body can be parsed as that content type.

Examples

GET requests

If a user makes a GET request to https://www.example.com/suite/webapi/customer?customerId=5 the value of http!request will be the following:

Field	Value
url	`https://www.example.com/suite/webapi/customer?customerId=5`
pathSegments	`{}`
queryParameters	`{customerId: "5"}`
headers	`{}`
body	`""`

In the above example, you can extract the value of the customer ID from the request using the expression http!request.queryParameters.customerId.

Expression	Value
`http!request.queryParameters.customerId`	`"5"`

However, if the user instead makes a GET request to https://www.example.com/suite/webapi/customer/5 with no headers the value of http!request will be the following:

Field	Value
url	`https://www.example.com/suite/webapi/customer/5`
pathSegments	`{"5"}`
queryParameters	`{}`
headers	`{}`
body	`""`

In the above example, you can extract the value of the customer ID from the request using the expression http!request.pathSegments[1].

Expression	Result Value
`http!request.pathSegments[1]`	`"5"`

Note that in both examples above, the ID of the customer was of type Text, not Number. This is because all HTTP URLs, including path and query parameters, are fundamentally text and not numbers. All values in the http!request.queryParameters and http!request.headers dictionaries are of type Text.

For more guidance on creating a GET API, check out this Appian Academy video:

POST requests

For POST requests, the body of the request is exposed in two fields: body and formData.

If a user makes a POST request to https://www.example.com/suite/webapi/customer where the body of the request contains id=7&name=Acme+Corporation&firstPurchaseDate=2016-03-12 and there a content type header with a value of application/x-www-form-urlencoded, the value of http!request will be the following:

Field	Value
url	`https://www.example.com/suite/webapi/customer/`
pathSegments	`{}`
queryParameters	`{}`
headers	`{Content-Type: "application/x-www-form-urlencoded"}`
body	`"id=7&name=Acme+Corporation&firstPurchaseDate=2016-03-12"`
formData	`{id:"7", name:"Acme Corporation", firstPurchaseDate:"2016-03-12"}`

If the same request did not contain a content type header or if it had a value other than application/x-www-form-urlencoded, the formData field of http!request would have been null.

When designing a web API, you can save a default value for your test HTTP request using the Set as default test values link. Once set, the default values will be saved with the interface.

For more guidance on creating a POST API, check out this Appian Academy video: