outMap.put("Books", "CollectionWrapper");
outMap.put("books", "Book");
provider.setOutTransformElements(outMap);
WebClient wc = WebClient.create("http://localhost:" + PORT + "/bookstore/books/adapter-list",
Collections.singletonList(provider));
Collection<? extends Book> books = wc.type("application/xml").accept("application/xml")
.postAndGetCollection(new Books(new Book("CXF", 123L)), Book.class);
assertEquals(1, books.size());
assertEquals(123L, books.iterator().next().getId());
}