REST Services. Zaenal Akbar

Transcription

1 PS/ Web Services REST Services Zaenal Akbar Friday, - -

2 Outline REST Services Overview Principles Common Errors Exercise

3 What is REST? Set of architectural principles used for design of distributed systems Focus on a system s resources A predominant Web service design model in the last few years displaced SOAP and WSDL-based interface design because it s a considerably simpler style to use

4 Principles of REST. Use HTTP methods explicitly. Be stateless. Expose directory structure-like URIs. Transfer XML, JavaScript Object Nota on (JSON), or both

5 . Use HTTP methods explicitly We have HTTP protocol on the Web, why not use it? CRUD (create, read, update, delete) opera ons and HTTP methods To create a resource on the server, use POST To retrieve a resource, use GET To change the state of a resource or to update it, use PUT To remove or delete a resource, use DELETE

6 HTTP Usage Use of HTTP methods for intended purposes The request URI in an HTTP GET request iden fies One specific resource Or the query string in a request URI Inconsistent use of HTTP GET State-changing opera on over HTTP GET Web caching tools (crawlers) and search engines could make server-side changes uninten onally

7 Use of HTTP POST Wrong: GET /adduser?name=robert HTTP/1.1 Right: POST /users HTTP/1.1 Host: myserver Content-Type: application/xml <?xml version="1.0"?> <user> <name>robert</name> </user>

8 Use of HTTP PUT Wrong: GET /updateuser?name=robert&newname=bob HTTP/1.1 Right: PUT /users/robert HTTP/1.1 Host: myserver Content-Type: application/xml <?xml version="1.0"?> <user> <name>bob</name> </user>

9 . Be Stateless ( ) Scalability and performance are needed on the Web Network topologies need requests to be self-contained for op mal load-balancing, rou ng, etc. A complete, independent request doesn t require the server, while processing the request, to retrieve any kind of applica on context or state Statelessness simplifies the design and implementa on of server-side components no need to synchronize session data

10 . Be Stateless ( ) Stateful request Stateless request

11 . Expose directory structure-like URIs The structure of a URI should be straigh orward, predictable, and easily understood. This type of URI is hierarchical, rooted at a single path, and branching from it are sub-paths that expose the service s main areas

12 URI Guidelines. Hide the server-side scrip ng technology file extensions (.jsp,.php,.asp).. Keep everything lowercase.. Subs tute spaces with hyphens or underscores (one or the other).. Avoid query strings as much as you can.. Instead of using the Not Found code if the request URI is for a par al path, always provide a default page or resource as a response.. URIs should also be sta c so that when the resource changes or the implementa on of the service changes, the link stays the same. This allows bookmarking.. It is also important that the rela onship between resources that is encoded in the URIs remains independent of the way the rela onships are represented where they are stored.

13 . Transfer XML, JSON, or both A resource representa on typically reflects the current state of a resource, and its a ributes, at the me a client applica on requests it The rela onships between data model objects (resources) should be reflected in the way they are represented for transfer to a client applica on Give client applica ons the ability to request a specific content type that is best suited for them, construct your service so that it makes use of the built-in HTTP Accept header

14 Common REST errors. Tunneling everything through GET You are using HTTP GET method for wri ng while your URIs do not iden fy a resource but some opera on you would like to perform on the resource. Ignoring response codes HTTP protocol has an extensive set of applica on-level response codes that you can use to describe various results of your API calls. Ignoring caching HTTP defines a powerful caching mechanism that include ETag ( If-None-Match ), If-Modified-Since header, and Not Modified response code Allow clients and servers to nego ate a fresh copy or through caching or proxy servers of a resource

15 Common REST errors. Ignoring hypermedia If your API calls send representa ons that do not contain any links, you are most likely breaking the REST principle called Hypermedia as the Engine of Applica on State (HATEOAS). Ignoring MIME types If resources returned by API calls only have a single representa on, you are probably only able to serve a limited number of clients that can understand the representa on You should use HTTP s content nego a on (supports various resource representa ons such as XML, JSON or YAML)

16 Useful Links. RESTful Web services: The basics, developerworks/webservices/library/ws-restful/. Create RESTful Web services with Java technology, http: // Building RESTful Web Services with JAX-RS, oracle.com/javaee/6/tutorial/doc/giepu.html. JAX-RS,

17 Task Assignment:. Download the worksheet from the course webpage. Complete the exercises in the worksheet. Upload it to the OLAT before the next session

18 Thank You