Chapter 20. Multipart Providers

RESTEasy has rich support for the multipart/* and multipart/form-data MIME (Multipurpose Internet Mail Extension) types. The multipart MIME format passes lists of content bodies. Multiple content bodies are embedded in the one message. multipart/form-data is often found in web application HTML Form documents, and is generally used to upload files. The form-data format works like other multipart formats, except that each inlined piece of content has a name associated with it.
RESTEasy provides a custom API for reading and writing multipart types, as well as marshaling arbitrary List (for any multipart type) and Map (multipart/form-data only) objects.

20.1. Input with multipart/mixed

When you write a JAX-RS service, RESTEasy provides an interface to let you read any multipart MIME type: org.jboss.resteasy.plugins.providers.multipart.MultipartInput. 
package org.jboss.resteasy.plugins.providers.multipart;

public interface MultipartInput
{
   List<InputPart> getParts();

   String getPreamble();
}

public interface InputPart
{
   MultivaluedMap<String, String> getHeaders();

   String getBodyAsString();

   <T> T getBody(Class<T> type, Type genericType) throws IOException;

   <T> T getBody(org.jboss.resteasy.util.GenericType<T> type) throws IOException;

   MediaType getMediaType();
}
MultipartInput is a simple interface that lets you access each part of the multipart message. Each part is represented by an InputPart interface, and is associated with a set of headers. You can unmarshal a part by calling one of the getBody() methods. The Type genericType parameter can be null, but the Class type parameter must be set. RESTEasy locates a MessageBodyReader based on the media type of the part, and the type information you pass in. The following piece of code unmarshals XML parts into a JAXB annotated class called Customer. 
   @Path("/multipart")
   public class MyService
   {
      @PUT
      @Consumes("multipart/mixed")
      public void put(MultipartInput input)
      {
         List<Customer> customers = new ArrayList...;
         for (InputPart part : input.getParts())
         {
            Customer cust = part.getBody(Customer.class, null);
            customers.add(cust);
         }
      }
   }
If you want to unmarshal a body part that is sensitive to generic type metadata, you can use the org.jboss.resteasy.util.GenericType class, like so: 
   @Path("/multipart")
   public class MyService
   {
      @PUT
      @Consumes("multipart/mixed")
      public void put(MultipartInput input)
      {
         for (InputPart part : input.getParts())
         {
            List<Customer> cust = part.getBody(new GenericType>List>Customer<<() {});
         }
      }
   }
GenericType is required here because it is the only way to obtain generic type information at runtime.