1. Overview of RESTful Web Services “A complex system that works is invariably found to have evolved from a simple system that worked.” – John Gall (Systemantics) 1©SoftMoore Consulting

2. Approaches to Distributed Processing Remote Procedure Call (RPC) –distributed functions CORBA/COM/DCOM –distributed objects (language independent) Java Remote Method Invocation (RMI) –distributed objects (Java-based) XML-RPC and Simple Object Access Protocol (SOAP) –distributed objects over the web (language independent) REST –distributed resources over the web 2©SoftMoore Consulting

3. What is a Web Service? An approach to using the web for distributed applications A software system designed to support interoperable machine-to-machine interaction over a network (W3C) An API that can be accessed over web and executed on a remote system hosting the requested service Characteristics of web services –communicate using open protocols such as XML, HTTP, etc. –range from such major services as storage management and CRM to much more limited services such as providing a stock quote and the checking of bids for an auction item. 3©SoftMoore Consulting

4. What is REST? REpresentational State Transfer (REST) – an approach to the design of software architectures for distributed hypermedia systems. Introduced in 2000 by Roy Fielding (one of the principal authors of HTTP) in his doctoral dissertation An architectural style centered around two basic principles: –resources as URIs –operations as HTTP methods Not a standard, but based on web standards –URIs, HTTP, HTML, XML, JSON, Atom, RDF, etc. Conforming to the REST constraints is often referred to as being “RESTful”. 4©SoftMoore Consulting

5. REST Architectural Style Characteristics and Constraints Client-server – separation of concerns (e.g., storage versus user interface) Stateless – each client request contains all the information necessary to service the request Cacheable – improves scalability and performance (Responses can define themselves as being cacheable or not.) Uniform interface (more on next slide) Layered system – intermediary servers can improve scalability via load balancing and shared caches Code on demand (optional) – servers can transfer logic to the client (e.g., JavaScript or Java applets) 5©SoftMoore Consulting

6. Guidelines for REST Interfaces Identification of resources using URIs Manipulations of resources through representations –Resources are conceptually separate from their representations. –A resource can have more than one representation, although one is usually designated as the default. Self-descriptive messages –Each message includes enough information to describe how to process the message (e.g., invoke an XML parser). Hypermedia as the engine of application state –Related resources are identified in the returned representation; e.g., via URIs. 6©SoftMoore Consulting

7. Components of a RESTful Web Service A base URI for the web service –e.g., http://example.com A set of resources with URI names relative to the base –e.g., http://example.com/order/1234 The MIME types of the data supported by the web service –e.g., XML, JSON, plain text, etc. The set of operations supported by the web service using HTTP methods –e.g., POST, GET, PUT, DELETE 7©SoftMoore Consulting

8. HTTP (Hypertext Transfer Protocol) Simple, stateless, request/response protocol –client opens connection and sends request message to server –server formulates and returns response message, usually containing the resource that was requested HTTP/1.1 message format –Initial line – three parts, separated by spaces Method name (GET, POST, HEAD, PUT, DELETE, etc.) Local path of the requested resource Version of HTTP being used (e.g., “HTTP/1.1”) –Zero or more lines known as headers –A blank line –An optional message body (e.g. a file, query data, etc.) ©SoftMoore ConsultingSlide 8 Note: HTTP/2 uses a binary protocol − no longer text-based.

9. Example: HTTP GET Request GET /HelloUser.jsp?name=John HTTP/1.1 Host: www.softmoore.com:80 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.7) Gecko/20070914 Firefox/2.0.0.7 Accept: text/xml,application/xml,application/xhtml+xml, text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive ©SoftMooreSlide 9 Note: Each header is on a single line (no line breaks). Line breaks are shown above to approve readability. Accept headers support content negotiation, resulting in possibly different representations of a resource.

10. Example: HTTP Response to a GET Method HTTP/1.1 200 Document follows Date: Tue, 14 Apr 2007 09:25:19 PST Server: JWS/1.1 Last-modified: Mon, 17 Jun 2005 21:53:08 GMT Content-type: text/html Content-length: 4435 ©SoftMooreSlide 10

11. Example: HTTP POST Request POST /servlet/MyServlet HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE 4.01; Windows NT) Host: www.softmoore.com:80 Accept: image/gif, image/x-xbitmap, image/jpeg, */ Content-type: application/x-www-form-urlencoded Content-length: 39 name=John&company=SoftMoore%20Consulting ©SoftMooreSlide 11 Note: A blank line signals the end of the POST request header and the beginning of the extended information.

12. Using the HTTP GET Method Properly The handling of a GET method is expected to be –safe: no side effects –idempotent: can safely be repeated Improper use of the HTTP GET method GET /adduser?name=moore HTTP/1.1 Host: www.softmoore.com:80 Proper use of HTTP – use POST method POST /users HTTP/1.1 Host: www.softmoore.com:80 Content-Type: application/xml moore 12©SoftMoore Consulting

13. CRUD/HTTP Mapping 13©SoftMoore Consulting CRUD Task HTTP Method Action CreatePOSTCreate a resource (without an ID) ReadGET Read a resource (no side effects, possibly cached) UpdatePUT Update (or possibly create) a resource with an ID DeleteDELETEDelete a resource

14. Resources Versus Representations A resource can be essentially any coherent and meaningful abstraction that may be addressed. A representation of a resource is typically a document that captures the current or intended state of a resource. A resource can have more than one representation – XML, JSON, PDF file, JPEG image, etc. 14©SoftMoore Consulting

15. Examples: Different Representations XML JSON 15©SoftMoore Consulting John Moore 123-456-7890 Charleston SC { "customer" : { "name" : "John Moore", "phone" : "123-45-6789", "city" : "Charleston", "state" : "SC" }

16. Basic Principles of REST Resources are identified by URIs. (Think URLs.) –URI “/” means parent-child or whole-part relationship (tree-like) –provide data to clients via gradual unfolding http://example.com/products/1234/reviews Clients communicate with resources via requests using a standard set of methods based on HTTP. Resources are manipulated through their representations, identified by media types. Responses can contain URIs that link to further resources. 16©SoftMoore Consulting

17. Using URI’s to Name Resources http://example.com/customers –all customers http://example.com/orders/ –all orders http://example.com/customers/1234 –customer with id 1234 http://example.com/orders/5678 –order with id 5678 http://example.com/customers/1234/orders –all orders for customer with id 1234 http://example.com/customers?last-name=moore –list of all customers with a last name of moore 17©SoftMoore Consulting

18. Examples: Using HTTP Methods 18©SoftMoore Consulting URI HTTP Method Action http://example.com/customersPOST Create a new customer. The ID is assigned by the service and is usually returned as part of the data returned by this operation. http://example.com/customersGET Retrieve a list of all customers with their member URIs for further navigation. http://example.com/customers/1234PUT Update (or possibly create) data for customer with ID 1234 http://example.com/customers/1234GET Retrieve a representation for the customer with ID 1234 http://example.com/customers/1234DELETEDelete customer with ID 1234

19. REST Anti-Patterns (Stefan Tilkov) Tunneling everything through GET or POST Ignoring caching Ignoring response codes Misusing cookies (e.g., to manage client sessions) Forgetting hypermedia Ignoring MIME types Breaking self-descriptiveness 19©SoftMoore Consulting

20. “Big” Web Services versus RESTful Web Services “Big” Web Services are based on SOAP and WS-* –heavyweight –have little to do with the web other than as a transport –disregards many HTTP capabilities such as authentication, caching, content type negotiation, etc. –designed to operate from a single URI with methods being invoked from within the request payload –expose internal algorithms through a complex programming- language-like interface that’s different for every service –mostly about invoking behavior 20©SoftMoore Consulting

21. “Big” Web Services versus RESTful Web Services (continued) RESTful web services are based on HTTP and URI’s –lightweight –designed to take advantage of the web and HTTP –expose data through a simple document-processing interface that is always the same –HTTP methods invoke behavior on resources accessed via URIs –mostly about managing information –not appropriate for every distributed application 21©SoftMoore Consulting

22. Impact of REST 22©SoftMoore Consulting Key evidence of this shift in interface design is the adoption of REST by mainstream Web 2.0 service providers – including Yahoo, Google, and Facebook – who have deprecated or passed on SOAP and WSDL-based interfaces in favor of an easier-to-use, resource-oriented model to expose their services.... If measured by the number of Web services that use it, REST has emerged in the last few years alone as a predominant Web service design model. In fact, REST has had such a large impact on the Web that it has mostly displaced SOAP- and WSDL-based interface design because it's a considerably simpler style to use. – Alex Rodriquez (IBM Software Engineer)

23. REST Framework Implementations Restlet (www.restlet.org) Java Specification Request (JSR) 311: JAX-RS: The Java API for RESTful Web Services –reference implementation is Jersey (https://jersey.dev.java.net/)https://jersey.dev.java.net/ Apache Sling Microsoft's Azure Services Python RIP Ruby On Rails PHP Symfony, Zend Framework Perl Catalyst REST 23©SoftMoore Consulting

24. References RESTFul Web Services by Leonard Richardson and Sam Ruby, O’Reilly Media, 2007. RESTful Java with JAX-RS 2.0 (Second Edition), Bill Burke, O’Reilly Media, 2013 Building RESTful Web Services with JAX-RS https://docs.oracle.com/javaee/7/tutorial/jaxrs.htm “Representational State Transfer,” Wikipedia article. https://en.wikipedia.org/wiki/Representational_state_transfer “RESTful Web Services: The Basics” by Alex Rodriguez, IBM developerWorks article, 2008. http://www.ibm.com/developerworks/webservices/library/ws-restful/ 24©SoftMoore Consulting