Implementing RESTful Web Services with Oracle Application Express

2. Implementing RESTful Web Services with Oracle Application Express

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4. Agenda • Introduction to REST • REST Modeling • APEX RESTful Services Use Cases • APEX RESTful Services Architecture • Walk through complete sample including: • Resources using GET, PUT, POST, DELETE methods • Testing, debugging • Authentication • Q & A

5. Introduction to REST

6. Examples • Public services with RESTful APIs: • Twitter, Netflix, Dropbox, Flickr, Amazon S3, ... • Products or tools with RESTful APIs • Glassfish Application Server Admin, Selenium WebDriver, ... • RESTful Frameworks • Jersey (JAX-RS), Restlet, Restify, APEX RESTful Services, ...

7. What is REST? • REST stands for Representational State Transfer. (Sometimes written ReST) • It describes an architecture for distributed information systems • First described in the 2000 doctoral dissertation “Architectural Styles and the Design of Network-based Software Architectures” by Roy Fielding. • It’s a description of how the Web works and why it works well

8. So what is REST? • Client – Server – request response • Stateless • Caching • Layered • Code on demand (optional) • Uniform interface: Request response style operations on named resources through self descriptive representations where state changes are via hyperlinks

9. Motivation and Characteristics • Hyper media • Optimized for large grained static (cacheable) messages • Internet scale • not just size or geography • many independent organizations • Extensibility, flexibility, responsiveness • “hypermedia as the engine of application state” • Application state is 100% on the client • The state or resources is persisted behind the servers

10. Benefits • Scalability – stateless, caching, gateways. Have more clients just add more servers or intermediaries. • Performance – caching, compression, incremental rendering, pre-fetch • Simple client – uniform interface means single client implementation can access any resource • Simple server – no extra layers and no state • No need for resource discovery due to hyperlinks • Reliability – redundancy – multiple servers • Separation of concerns and uniform interface allows clients and servers to change and be developed independently

11. Uniform Interface ResourcesNouns Unconstrained The REST Triangle: • Resources • Methods • Representations MethodsVerbs Constrained RepresentationsHyper Linked Constrained

12. Uniform Interfaces - Resources • Key abstract concept • Identified by a URI • Distinct from underlying storage • Semantics fixed • Value may change over time • Can have multiple URIs • Can have multiple representations • Examples: • http://example.org/NewOrleans/traffic/10 • http://example.org/traffic/NewOrleans/I10 • http://foo.com/store/orders ResourcesNouns Unconstrained MethodsVerbs Constrained RepresentationsHyper Linked Constrained

13. User Interface - Methods • Constrained set • GET safe • PUT idempotent • DELETE idempotent • POST not safe or idempotent • Apply to the resource • GET retrieve • PUT update (or create) • DELETE delete • POST create sub resource • Response codes 1xx, 2xx, 3xx, 4xx, 5xx ResourcesNouns Unconstrained MethodsVerbs Constrained RepresentationsHyper Linked Constrained

14. User Interface - Representations • Not the actual resource • Constrained set • Self-descriptive • media type (Content-Type) • text/html • application/json • Includes metadata • Understood by all components • May be for humans, machines or both • Negotiated ResourcesNouns Unconstrained MethodsVerbs Constrained RepresentationsHyper Linked Constrained

15. REST Modeling - How to design a RESTful API

16. REST Modeling • Its different from: • Object modeling • Entity Relationship modeling • Resources are the key abstraction • What are the resources • What methods does each support • What representation(s) to use • Relationships via linking

17. REST Modeling - Resources • Start by identifying the resources • Similar to thinking about entities but... • Resources are not result sets (rows and columns) • They are “documents” • Two main types • Collections • Items

18. REST Modeling - URIs • Human readable (not necessary but it helps) • Tends to form a hierarchy • Use the query part appropriately • Use to search, filter, or possibly specify a mode • Identification of the resource is better in the path • (preferred) http://example.com/orders/100234 • http://example.com/orders?id=100234 • Don’t make them verbs! • (bad) http://example.com/accounts/addaccount

19. REST Modeling - Representations • The usual suspects: • text/html • application/xml • application/json • application/x-www-form-urlencoded (for input: PUT, POST) • And others: images: svg, jpg, png etc., text/css, text/javascript • How many does each resource need? • Remember it is all about hyper media. Include links.

20. REST Modeling - Methods But it’s not that simple …

21. REST Modeling - Methods

22. REST Modeling - Methods • The difference between POST and PUT is in the meaning of the request URI • For PUT the URI is the resource that will be created or updated • For POST the URI is the container of the resource that will be created. The server gets to assign a URI to the resource • Conditional GET • Optimistic concurrency for PUT • Use method response codes appropriately

23. APEX RESTful Services Use Cases

24. Example Use Cases • Creating a native mobile application using same database as corresponding APEX web application • Integration with back office operations • Data collection • Synchronization • Configuration management • Provide data persistence for a static single page web app • You have some interesting data you want to share with the world

25. Reasons for using APEX RESTful Services • Implement resources close to the data • Leverage your experience with PL/SQL • Make use of existing logic in packages • Use existing APEX workspace and APEX Listener

26. Considerations • APEX Listener is required • Keep up with the latest version • Demo’s were done using version 2.0.3 • Authentication is needed for most real world situations • OAuth2 and APEX application authentication are supported • When making REST calls from a browser, either: • Serve the calling web page from the same origin, or • Use a modern browser that supports cross origin requests (CORS) • Another option is to make the call from the server

27. APEX RESTful Services Architecture

28. Architecture Diagram Client APEX Listener APEXBuilder APEXMetadata

29. Definition metadata • RESTful Service Module • Resource Templates • Handler

30. What the Listener does for you • Request dispatching • JSON generation for simple GET requests • Pagination • Lower cases column names • Null values are omitted • Generating JSON links • Simple JSON parsing, form data parsing • Exception and error handling and responses (HTML)

31. Authentication • First party authentication • Standard APEX authentication • Must be in same workspace • Third party authentication • OAuth2 • Authorization code flow • Implicit grant flow

32. Handler Interface - Inputs • Pagination control – :page_size, :page_offset, :row_offset, :row_count • For authenticated requests – :current_user • Parameters from the URI template become bind variables • Request entity – :content_type, :body • Request entity – A simple JSON object is parsed and creates a bind variable for each property. A x-www-form-urlencoded body is parsed and creates a bind variable for each parameter. • Any HTTP request header can be mapped to a bind variable • Special pseudo headers from listener • OWA environment OWA_UTIL.GET_CGI_ENV

33. Handler Interface – Inputs continued • Special pseudo headers from Listener • X-APEX-BASE – the base URL of the request • X-APEX-PATH – the path of the request relative to the base • X-APEX-CHARSET – the character set of the request body • X-APEX-METHOD – the HTTP method used to make the request • X-APEX-PREFERRED-CONTENT-TYPE - from parsing the Accept HTTP request, identifies the MOST preferred content type that the client would like to receive

34. Handler Interface - Outputs • Any HTTP response header can be mapped to a bind variable • OWA context: htp.p etc. • Special pseudo headers for Listener • X-APEX-STATUS - Specifies the numeric HTTP status code to generate for the response • X-APEX-FORWARD - Specifies the location of a resource that Listener should return as the response to this request.

35. APEX RESTful Services Sample Walk Through

36. Example RESTful Service Module • Uses the tables from the APEX Sample Database Application • DEMO_CUSTOMERS, DEMO_PRODUCT_INFO, DEMO_ORDERS, DEMO_ORDER_ITEMS • APEX version 4.2.2, Listener 2.0.3 • Uses pl/json open source JSON library • You need to install this library to use the sample • http://pljson.sourceforge.net/

37. Common Pattern employes/ • GET - Retrieves list of all employees. • POST - Create a new employee. employes/{empno}/ • GET - Retrieves details for a specific employee. • PUT - Updates the specific employee. • DELETE - Deletes the employee.

38. Testing Tips • Use APEX RESTful Services Test Client (resttest.html) • Use Firebug or developer tools to examine HTTP requests and responses • Look at Error-Reason header • Do initial browser testing from same origin • Browsers hide error information when going cross origin • Another Java based test tool: rest-client from WizTools.org

39. Reference Material

40. REST References • RESTful Web Services, by Leonard Richardson and Sam Ruby, available from O’Reilly Media at http://oreilly.com/catalog/9780596529260/ • Wikipedia: http://en.wikipedia.org/wiki/Representational_State_Transfer • The source: http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htmmostly chapters 5 and 6 • A nice 14 minute video introduction: http://www.youtube.com/watch?v=YCcAE2SCQ6k • HTTP spec: http://tools.ietf.org/html/rfc2616 • URI spec: http://tools.ietf.org/html/rfc3986 • JSON format: http://json.org/ • Other specs like HTML, XML etc. from w3.org

41. APEX RESTful Services References • Application Express on OTN http://otn.oracle.com/apex • The example module TBD • APEX RESTful Service Test Client TBD • RESTful Services Dev Guide (restful_services_devguide.html) in the Listener download zip file doc folder

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