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Developing Restful-API using JAX-RS

Web Services 

  • Services that are exposed to the Internet for programmatic access. 
  • Two main types of web services
    • REST (Representational State Transfer)
      • REST has no standard protocol (can use XML,JSON,etc)
    • SOAP
  • Web services use HTTP (Hyper Text Transfer Protocol) to send and receive messages.
  • To include service definitions that offered from Web Service: WSDL

URI

  • Two main types of URI
    • Resource Based URI
      • Every resource must be identified by a single URI 
      • Doesn't contain .do in URI ( /message/{message_Id})
    • Collection URI
      • return collection of instances
      • ex : /message/1/comments -> return all the comments relevant to message id=1
      • To create new resource you have to use collection URI

Filtering  

  • /messages?offset=30&limit=10 -> return 10 messages starting from message_Id=30

HTTP Methods 

  • Four main types of HTTP methods:
    • Get: To get the details of resource
    • Put: To update resources
    • Post: To create new resource
    • Delete: To delete the resource
  • Other HTTP methods: head, options
  • HTTP methods can be in two types
    • Idempotent: safely repeatable (put, get, delete)
    • Non-idempotent: can not safely repeatable (post)

Status Codes

  • Five main types of status code that indicate by first number of three digits
    • 1xx: Informational codes (acknowledgement/response)
    • 2xx: Success codes
    • 3xx: Redirection codes (ask clients do something)
    • 4xx: Client Error Codes
    • 5xx: Server errors

Hypermedia As The Engine Of Application State(HATEOAS)

  • Use to provide links to resources
  • rel: Describe the relationship to a current resource (What that link point to)

API Levels 

  • Three main types of API levels
    • Level1: Use resource based URI
    • Level2: Use HTTP methods
    • Level3: Use HATEOAS

Additional Information 

  • Hypertext: Text that contains links to other texts (hyperlinks)
  • Static web pages : Every resource has URI and specific HTML file
  • Jersey: Library that handles all the API functionalities in the deploying server (ex: tomcat)
  • Maven: Project management utility
    • Archetype: template (previously created projects)
    • Group id: Package id
    • Artifact Id: project name 

Implementing Messenger App Using Jax-RS

  • Create Maven project 
    • select archetype as Jersey-webapp
  • Crete tomcat server
  • Create resources
    • @Path(/messages): To choose class
    • @GET: Tell the relevant HTTP method
    • @produces(MediaType.TEXT_PLAIN): Tell the return type
    • @XmlRootElement: convert types to XML type
  • Create database class using hashmap
  • Include a variable in a path parameter
    • @Path("/{message_id}") : use curly braces
    • get this one as a variable to the method: use @PathParam
  • To get JSON type: uncomment dependencies in pom.xml file
  • For post requests
    • @consumes(MediaType.TEXT_PLAIN) : Tell the posting data type
  • Send Parameters
    • @QueryParam("year") : /messages?year=2015
      • Query param use? 
    • @MatrixParam("year"): /message;year=2015
      • Matrix param use;
    • @HeaderParam("year")
      • To get header values by their name
    • @CookieParam("year")
      • To get cookie values
    • @Context UriInfo uriinfo: To get all the information if you are not sure about values
      • To get all the necessary parameters (path, URL, query, cookies etc)
    • @BeanParam : @BeanParam BeanParam(class name) beanparam
      • Save other parameters in a class and access them using getters and setters
  • @XmlTransient: ignore the below data when you expose other data 
  • To change headers: use Response.created()
  • To create URI : use uriinfo.getAbsolutePathBuilder()
  • To handle the exception: use WebApplicationException

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