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Define media types for resources in RESTful applications

Resources are represented by multiple formats. XML, JSON, Atom, binary formats such as PNG, JPEG, GIF, plain text, and proprietary formats are used to represent resources. Representational State Transfer (REST) provides the flexibility to represent a single resource in multiple formats.

Define the resources in the JAX-RS web application. Resources have representations. A resource representation is the content in the HTTP message sent to, or returned from the resource using the URI. Each representation that a resource supports has a corresponding media type. For example, if a resource is going to return content formatted as XML, we can use application/xml as the associated media type in the HTTP message.

Depending on the requirements of the application, resources can return representations in a preferred single format or in multiple formats. For example, resources that are accessed using JavaScript clients might prefer JSON representations because JSON is easy to consume.

JAX-RS provides @Consumes and @Produces annotations to declare the media types that are acceptable for a resource method to read and write.

JAX-RS also maps Java types to and from resource representations using entity providers. A MessageBodyReader entity provider reads a request entity and deserializes the request entity into a Java type. A MessageBodyWriter entity provider serializes from a Java type into a response entity.

Standard entity providers and basic Java types. This table includes the standard entity providers and basic Java types that are included in the JAX-RS runtime environment, along with the corresponding supported content types.

Java type MessageBodyReader MessageBodyWriter Supported Content types
byte[] X X */*
java.io.InputStream X X */*
java.io.Reader X X */*
java.lang.String X X */*
java.io.File X X */*
javax.activation.DataSource X X */*
javax.xml.transform.Source X X text/xml, application/xml, application/*+xml
javax.ws.rs.core.MultivaluedMap X X application/x-www-form-urlencoded
JAXB types X X text/xml, application/xml, application/*+xml
javax.ws.rs.core.StreamingOutput   X */*

If a String value is used as the request entity parameter, the MessageBodyReader entity provider deserializes the request body into a new String. If a JAXB type is used as the return type on a resource method, the MessageBodyWriter serializes the JAXB object into a response body.

If you need a custom mapping from a Java type to a specific representation, see the information for using an application-defined entity provider.

If your client can handle multiple formats and you want the server to determine the best resource representation to return, read about using content negotiation in JAX-RS applications to serve multiple content types.

The specifications for XML, JSON, and Atom provide details regarding the formats of resource representations for applications. See the specifications to learn more about the formats of resource representations.

  1. Determine the resource representation format such as XML, JSON, or ATOM to use for either the request or the response.

  2. Add the @Consumes and @Produces annotations appropriately to the resource method.

  3. If the resource needs to read the content of the request, add a request entity parameter to the resource method. The request entity parameter is a single Java parameter on the method that does not have an annotation.

  4. If the resource method returns content in the response, return a Java object that is writable by a JAX-RS entity provider. This Java object is mapped to the response entity in the HTTP response. The returned object must be a JAX-RS supported Java type or wrapped in a javax.ws.rs.core.Response or javax.ws.rs.core.GenericEntity type.


Results

You have mapped the request entities to the resource method entity parameter and any response objects that are returned are mapped to the response entity for the resource representation.


Example

The following example illustrates defining XML as the resource representation for a RESTful bookstore application.

  1. Identify the resource methods to read the request entity or return a response entity.

    In the retrieveSpecificBookInformation method example that follows, there is no request entity that is read. However, there is a response object that is returned. This object wraps a JAXB object containing the entity information. Adding the @Produces annotation on the resource method with a media type of application/xml indicates the resource method always returns an XML representation with a media type of application/xml.

    Clients that have an Accept HTTP request header value compatible with the application/xml media type invoke the method correctly.

    Clients that do not have an Accept HTTP header value compatible with the application/xml media type automatically receive a 406 Not Acceptable response status which indicates the server cannot produce an acceptable response.

    The following example identifies the resource methods that read the request entity or return a response entity: 

    /*
 * Book.java
 * This class represents individual books. The @Produces annotation specifies a media type of application/xml.
 */
@Path(“/bookstore/books/{bookID}”)
public class Book {
  @GET
  @Produces(“application/xml”)
  public javax.ws.rs.core.Response retrieveSpecificBookInformation(@PathParam(“bookID”) String theBookID,
   @Context javax.ws.rs.core.HttpHeaders headers) {
   /* … */
   return     Response.ok(/* JAXB object to represent response body entity */).expires(/* Expires response header value*/).header(“CustomHeaderName”, “CustomHeaderValue”).build();
   }
   @PUT
   public String updateBookInformation(@PathParam(“bookID”) String theBookID, String theRequestEntity,
    @javax.ws.rs.HeaderParam(“Content-Length”) String contentLengthHeader) { /* … */ }

   @DELETE
   public void removeBook(@PathParam(“bookID”) String theBookID) { /* … */ }}

  2. Identify the resource methods that need to consume the request information.

    In the following snippet, the PUT method on the book resource accepts the request entity content if a media type of text/plain is sent, as defined in the @Consumes annotation. This method returns content with a text/plain representation as specified in the @Produces annotations.

    If a client does not send a message with a Content-Type value of text/plain, then the PUT resource method is not invoked. If Content-Type: application/xml is sent in the HTTP request headers, the updateBookInformation Java method is not be called.

    The DELETE method neither reads a request entity nor returns a response entity; therefore, it does not require either an @Consumes or an @Produces annotation.

    The following example identifies the resource methods that consume the request information: 

    /*
 * Book.java
 * This class represents represent individual books with custom headers.
 */
@Path(“/bookstore/books/{bookID}”)
public class Book {
  @GET
  @Produces(“application/xml”)
  public javax.ws.rs.core.Response retrieveSpecificBookInformation(@PathParam(“bookID”) String theBookID, @Context javax.ws.rs.core.HttpHeaders headers) {
    /* … */
    return Response.ok(/* JAXB object to represent response body entity */).expires(/* Expires response header value).header(“CustomHeaderName”, “CustomHeaderValue”).build();
  }
  @PUT
  @Consumes(“text/plain”)
  @Produces(“text/plain”)
  public String updateBookInformation(@PathParam(“bookID”) String theBookID, String theRequestEntity, @javax.ws.rs.HeaderParam(“Content-Length”) String contentLengthHeader) {
    /* … */
    String responseEntity = /* a plain text representation */;
    return responseEntity;
  }

  @DELETE
  public void removeBook(@PathParam(“bookID”) String theBookID) { /* … */ }}

See the JAX-RS specification for a list of all the standard media formats that are supported for representations.

Advanced users might consider defining custom mappings of Java types to representations or using content negotiation for clients to negotiate preferred resource representations. To learn more about these options, see the using custom defined entity formats information or the serving multiple content types with content negotiation information.


Related


Define the resources in RESTful applications
Define the URI patterns for resources in RESTful applications
Define resource methods for RESTful applications
Define the HTTP headers and response codes for RESTful applications
Define parameters for request representations to resources in RESTful applications
Use custom entity formats
Use content negotiation to serve multiple content types in JAX-RS applications


Reference:

Web services specifications and APIs


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