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How-to: REST Web services demystified

REST API integration needn't be daunting -- get started with web services

By Kirsten Jones, InfoWorld, 08/23/12

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These days, REST APIs are available to integrate your application or website with thousands of platforms -- Web 2.0 properties such as Twitter, Facebook, and Foursquare, as well as old-school companies like USA Today, Best Buy, and Edmunds.com. Unfortunately, tapping this dizzying buffet of options isn't always easy.

Most API documentation assumes an understanding of the foundational technology, and while REST API architecture gives developers enormous freedom to innovate, that freedom comes at a price -- namely, fewer guidelines for application behavior. But because these APIs are based on HTTP, a mature protocol, there are numerous strategies you can use to develop and debug your application. First, though, you need a comprehension of the basics of HTTP, a grasp of REST architecture, and some tools for inspecting traffic and strategies for debugging problems.

More about REST

Learn more about REST Web services in the Java enterprise:

HTTP
HyperText Transfer Protocol (HTTP) -- the protocol used throughout the Internet for transactions between Web servers and clients -- is simple, tested, and supported by libraries in every modern programming language. HTTP includes methods supporting all of the necessary actions for a server/client transaction: PUT, GET, POST, and DELETE. It has a rich set of status codes to cover success and error situations, and headers and query parameters make it possible to send additional information about the transaction or request to the server.

To better illustrate how HTTP works, let's take a look at a simple transaction. This is a basic request from a Chrome browser on a Macintosh to Google's home page.

Request

1   Method: GET

2   URL: http://www.google.com

3   Headers:

           Accept: text/html

           Accept-Language: en-US

           User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3)

Looking over the request, you can see that the method sent (1) was GET -- a read operation on an HTTP resource. The URL (2) indicates the full path being retrieved -- in this case, the document at the root of http://www.google.com. The request gets a little more interesting with the headers (3). An HTTP transaction can have any number of headers, and these allow the client to send information about the transaction to the server.

In addition to the types of headers seen here, headers can also be used to send user-specific information such as cookies. Servers aren't under any obligation to use information passed along via headers, but they frequently use the information to craft the response appropriately -- HTML that will display nicely on a specific browser, or content in the language the user prefers.

Response

4   Status: 200

5   Content: <a bunch of html>

6   Headers:

           Content-Length: 24716

           Content-Type: text/html; charset=UTF-8

           Date: Fri, 11 May 2012 21:26:46 GMT

The response from Google includes information that is useful to the client -- and that can be useful to you too. The first and most important piece is (4) the HTTP Status code. This code is returned with every response from an HTTP server. Understanding these codes makes it a lot easier to figure out what's happening between the client and the server.


For more enterprise computing news, visit InfoWorld. Story copyright InfoWorld Media Group, Inc.

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