Building RESTful Web Services with JAX-RS – Annotations

Post moved to

http://srinichekuri.com/2016/01/17/building-restful-web-services-with-jax-rs-annotations/

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Let’s take a look at annotations that are used to build RESTful services. Based on the implementation framework that you are using, there might be many annotations. In this post we will discuss annotations that are supported by JAX-RS specs only.

@Path

• @Path annotation identifies URI Path template
• Can be used at class or method level.
• Always specifies relative url to base url (host)
• @Path value need not have leading or tailing slashes (/). JAX-RS treats them them the same either ways
• Variables can be specified in @path as follows 
  • Multiple Variables can be specified. Eg @Path(“/users/{username_1}/{username_2}”)

 

//Variable in path is specified by {}
@Path("/users/{username}")
public class UserResource {

    @GET
    @Produces("text/xml")
    //variable specified in @Path can be accessed by @PathParam
    public String getUser(@PathParam("userName") String userName) {
        ...
    }
}




Request Method Designator Annotations (@GET, @POST, @PUT, @DELETE and @HEAD):

• @GET – The Java method annotated with this will process HTTP GET requests.

• @POST – The Java method annotated with this will process HTTP POST requests.
• @PUT – The Java method annotated with this will process HTTP PUT requests.
• @DELETE – The Java method annotated with this will process HTTP DELETE requests.
• @HEAD – The Java method annotated with this will process HTTP HEAD requests.

Few logistics that should be followed to use JAX-RS for request methods designator annotations are as follows

• Methods decorated with request method designators must return following:
  • void
  • A Java programming language type
  • A javax.ws.rs.core.Response Object.
• Multiple parameters may be extracted from the URI using @PathParam or @QueryParam (Explained below).
• The HTTP PUT and POST methods expect an HTTP request body.
• Both @PUT and @POST can be used to create or update a resource.
• POST can mean anything, so any semantics can be used. PUT has well defined semantics.When using PUT for creation, the client declares the URI for the newly created resource.
• A common pattern is to use POST to create a resource and return a 201 response with a location header value is the URI to the newly created resource. In this pattern, the web service declares the URI for the newly created resource.

@Consumes and @Produces

@Produces annotation is used to specify the MIME media type that are sent back to client.

• If specified on class level, all methods will follow it.
• One can override class level by specifying this on method level.
• If no methods in a resource are able to produce the MIME type in a client request, then JAX-RS runtime sends back an HTTP ‘406 Not Acceptable’ error.
• Multiple MIME-types can be specified as follows
  • @Produces({“image/jpeg,image/png”})

   

 

@Path("/myResource")
@Produces("text/plain")
public class SomeResource {
    @GET
    public String doGetAsPlainText() {
        ...
    }

    @GET
    @Produces("text/html") //overides class level
    public String doGetAsHtml() {
        ...
    }
}




@Consumes represents the media types a resource  can accept.

• If specified on class level, all methods will follow it.
• One can override class level by specifying this on method level.
• If a resource is unable to consume the MIME type of a client request, the JAX-RS runtime sends back an HTTP “415 (‘Unsupported Media Type’)” error.
• If @consumes is used on method that returns ‘void’ then HTTP 204 (‘No Content’) error is returned.
  

  @POST@Consumes(“text/plain”)public void postClichedMessage(String message) {    // Store the message }

@Path("/myResource")
@Consumes("multipart/related")
public class SomeResource {
    @POST
    public String doPost(MimeMultipart mimeMultipartData) {
        ...
    }

    @POST
    @Consumes("application/x-www-form-urlencoded")
    public String doPost2(FormURLEncodedProperties formData) {
        ...
    }
}

 

Request Parameters (@QueryParam, @PathParam, @DefaultValue, @MatrixParam, @HeaderParam, @CookieParam, @FormParam)

• @QueryParam indicates URI query parameter.Eg: http://<host>/testService?testQueryParam=1
• @PathParam indicates path Parameter. Eg: http://<host>/testService/testPathParam/1/
• @DefaultValue indicates the default value to be used when parameter is not sent. If any of the parameters are not successfully parsed to Java type. an HTTP 400 (‘Client Error’) response is returned.

Both @QueryParam and @PathParam can be used only on following Java types:

• All primitive types except char.
• All wrapper classes of primitive types except Character
• Any class with a constructor that accepts a single String argument.
• Any class with static method named valueOf (String) that accepst a single String argument
• List<T>, Set<T> or SortedSet<T>, where T matches the already listed criteria.

 

@Path("smooth")
@GET
public Response smooth(
        @DefaultValue("4") @QueryParam("number") int colorNumber,
        @DefaultValue("red") @QueryParam("last-color") String color
        ) { ... }