RESTful Services. Sistemi Informativi Aziendali A.A. 2012/2013

Transcript

1 RESTful Services

2 Summary Foundations REST in Java

3 Foundations

4 REST Representational State Transfer Firstly defined by Roy Fielding (2000) Architectural Styles and the Design of Network-based Software Architectures Has mostly displaced Web Services Simpler Standard E.g. Will be part of the Java distribution through JSR-311

5 Basic Principles Addressability Use HTTP methods explicitly GET, PUT, POST, DELETE Stateless Atomic requests (no state preservation between different requests) Expose directory structure-like URIs Resources identified by URIs Transfer XML, JavaScript Object Notation (JSON) or both

6 Resource Resource Thing exposed by the system to the outside world Everything is a resource Independent from its representation bonino.html bonino.jpg

7 Operations on Resources GET PUT Defines a reading access of the resource without side-effects. The resource is never changed via a GET request (idempotent*). Updates/changes an existing resource (idempotent*) DELETE POST Removes the resources (idempotent*). Creates a new resource, must also be idempotent*. * Idempotent operations can get repeated without leading to different results.

8 Examples Accessing a resource (read) GET /users/robert HTTP/1.1 Creating a resource POST /users HTTP/1.1 Host: myserver Content-Type: application/xml <?xml version="1.0"?> <user> <name>robert</name> </user>

9 Examples Changing a resource To change the resource Robert Provide a new representation for Robert in the body of a PUT request The old representation will not be accessible anymore PUT /users/robert HTTP/1.1 Host: myserver Content-Type: application/xml <?xml version="1.0"?> <user> <name>bob</name> </user>

10 Examples Delete a resource DELETE /users/robert HTTP/1.1

11 REST in J2EE

12 REST in J2EE JSR-311 Aka JAX-RS Reference implementation Jersey Client Server Restful resources identified through annotations

13 Jersey Annotations

14 Jersey + Eclipse REST server

15 Jersey + Eclipse REST public class HelloREST { // This method is called if TEXT_PLAIN public String sayplaintexthello() { return "Hello Jersey"; } } // This method is called if XML public String sayxmlhello() { return "<?xml version=\"1.0\"?>" + "<hello> Hello Jersey" + "</hello>"; }

16 Jersey + Eclipse REST server <?xml version="1.0" encoding="utf-8"?> <web-app xmlns:xsi=" xmlns=" <display-name>it.polito.sistinfo.services.rest</display-name> <servlet> <servlet-name>jersey REST Service</servlet-name> <servlet-class>com.sun.jersey.spi.container.servlet.servletcontainer</servlet-class> <init-param> <param-name>com.sun.jersey.config.property.packages</param-name> <param-value>it.polito.sistinfo.services.rest</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>jersey REST Service</servlet-name> <url-pattern>/rest/*</url-pattern> </servlet-mapping> </web-app>

17 Jersey+Eclipse - Client Jersey provides a client library to consume REST services Clients can alternatively exploit Apache Http Client Example Google Directions API Client c = Client.create(); c.setfollowredirects(true); WebResource r = c.resource(" MultivaluedMap<String, String> params = new MultivaluedMapImpl(); params.add("origins", "cuneo"); params.add("destinations", "torino"); params.add("language", "it-it"); params.add("sensor", "false"); //send the query JSONObject responseasjson = r.path("json").queryparams(params).get(jsonobject.class); //print out the query out.println(r.path("json").queryparams(params).geturi()); out.println("<br/>"); //print out the response out.println(responseasjson.tostring());

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