The Java EE 6 Tutorial, Volume I

Using Entity Providers to Map HTTP Response and Request Entity Bodies

Entity providers supply mapping services between representations and their associated Java types. There are two types of entity providers: MessageBodyReader and MessageBodyWriter. For HTTP requests, the MessageBodyReader is used to map an HTTP request entity body to method parameters. On the response side, a return value is mapped to an HTTP response entity body using a MessageBodyWriter. If the application needs to supply additional metadata, such as HTTP headers or a different status code, a method can return a Response that wraps the entity, and which can be built using Response.ResponseBuilder.

The following list contains the standard types that are supported automatically for entities. You only need to write an entity provider if you are not choosing one of the following, standard types.

The following example shows how to use MessageBodyReader with the @Consumes and @Provider annotations:

public class FormReader implements MessageBodyReader<NameValuePair> {

The following example shows how to use MessageBodyWriter with the @Produces and @Provider annotations:

public class FormWriter implements MessageBodyWriter<Hashtable<String, String>> {

The following example shows how to use ResponseBuilder:

    public Response getItem() {
        System.out.println("GET ITEM " + container + " " + item);
        Item i = MemoryStore.MS.getItem(container, item);
        if (i == null)
            throw new NotFoundException("Item not found");
        Date lastModified = i.getLastModified().getTime();
        EntityTag et = new EntityTag(i.getDigest());
        ResponseBuilder rb = request.evaluatePreconditions(lastModified, et);
        if (rb != null)
        byte[] b = MemoryStore.MS.getItemData(container, item);
        return Response.ok(b, i.getMimeType()).