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Implementing RESTful Web
Services with
Oracle Application Express
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The following is intended to outline Oracle’s general
product direction. It is intended for information
purposes only, and may not be incorporated into any
contract. It is not a commitment to deliver any
material, code, or functionality, and should not be
relied upon in making purchasing decisions.
The development, release, and timing of any
features or functionality described for Oracle’s
products remains at the sole discretion of Oracle.
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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
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Introduction to REST
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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, ...
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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
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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
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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
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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
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Uniform Interface
The REST Triangle:
• Resources
• Methods
• Representations
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Resources
Nouns Unconstrained
Methods
Representations
Verbs Constrained
Hyper Linked Constrained
Uniform Interfaces - Resources
• Key abstract concept
• Identified by a URI
• Distinct from underlying storage
• Semantics fixed
Resources
Nouns Unconstrained
• 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
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Methods
Representations
Verbs Constrained
Hyper Linked Constrained
User Interface - Methods
• Constrained set
–
–
–
–
GET safe
PUT idempotent
DELETE idempotent
POST not safe or idempotent
Resources
Nouns Unconstrained
• Apply to the resource
–
–
–
–
GET retrieve
PUT update (or create)
DELETE delete
POST create sub resource
• Response codes 1xx, 2xx, 3xx,
4xx, 5xx
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Methods
Representations
Verbs Constrained
Hyper Linked Constrained
User Interface - Representations
• Not the actual resource
• Constrained set
• Self-descriptive
• media type (Content-Type)
Resources
Nouns Unconstrained
• text/html
• application/json
• Includes metadata
• Understood by all components
• May be for humans, machines or both
• Negotiated
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Methods
Representations
Verbs Constrained
Hyper Linked Constrained
REST Modeling How to design a
RESTful API
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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
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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
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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
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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.
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REST Modeling - Methods
REST
CRUD
SQL
GET
Read
SELECT
POST
Create
INSERT
PUT
Update or
Create
UPDATE or
INSERT
DELETE
Delete
DELETE
But it’s not that simple …
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REST Modeling - Methods
REST
CRUD
SQL
But …
GET
Read
SELECT
Keep it safe. Make sure there are
no side effects
POST
Create
INSERT
Also for other non-safe,
non-repeatable changes
PUT
Update or
Create
UPDATE or
INSERT
Keep it repeatable with same results
(idempotent)
DELETE
Delete
DELETE
Keep it repeatable with same results
(idempotent)
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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
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APEX RESTful Services
Use Cases
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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
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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
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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
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APEX RESTful Services
Architecture
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Architecture Diagram
APEX
Builder
Client
APEX
Listener
APEX
Metadata
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Definition metadata
• RESTful Service Module
• Resource Templates
• Handler
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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)
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Authentication
• First party authentication
• Standard APEX authentication
• Must be in same workspace
• Third party authentication
• OAuth2
• Authorization code flow
• Implicit grant flow
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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
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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
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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.
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APEX RESTful Services
Sample Walk Through
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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/
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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.
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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
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Reference Material
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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.htm
mostly 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
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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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@vuvarovs
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