How to inherit RequestMappings in a Spring 3 MVC REST API

I'm trying to build a RESTful API using Spring MVC. I'm shooting for clean and manageable code where the package structure follows the url structure.

So here is what I've got:

// com.test.api.library
@RequestMapping("/library/{libraryId}")
public Library getLibrary(@PathVariable long libraryId) {
   return service.getLibraryById(libraryId);
}

// com.test.api.library.book
@RequestMapping("/library/{libraryId}/book/{bookId}")
public Book getBook(@PathVariable long libraryId, @PathVariable long bookId) {
   Library library service.getLibraryById(libraryId);
   return library.getBookById(bookId);
}

While this works, I find it messy and error-prone to have to repeat "/library/{libraryId}" in all inherited @RequestMappings, /library is likely to be to root of a big part of the API and it should be written once and reused instead of written everywhere.

I would like to rewrite the book-class to something like this:

// com.test.api.library.book
@RequestMapping("/book/{bookId}")
public Book getBook(@PathVariabl开发者_如何学编程e long bookId) {
   // long libraryId magically given to me from the library-class's getLibrary()

   Library library service.getLibraryById(libraryId);
   return library.getBookById(bookId);
}

Is there any way Spring can help me here? It is acceptable for me to use normal java inheritance, spring annotation or anything else that helps me to not write "/library/{libraryId}" as a part of every url I ever write.

I believe this question has been asked & answered before: Spring MVC @RequestMapping Inheritance

That said, here is one way to reduce the amount of duplicate information. I don't actually do this in my own code because I think having the URI right next to the code is more maintainable, even if it means a little duplication.

@RequestMapping(URI_LIBRARY)
public interface LibraryNamespace {
  public static String URI_LIBRARY = "/library/{libraryId}";
}

@RequestMapping(URI_BOOK)
public interface BookNamespace {
  public static String URI_BOOK = LibraryNamespace.URI_LIBRARY + "/book/{bookId}";
}

@Controller
public class LibraryController implements LibraryNamespace {
  @RequestMapping("")
  public Library get(@PathVariable long libraryId) {
    return service.getLibraryById(libraryId);
  }
}

@Controller
public class BookController implements BookNamespace {
  @RequestMapping("")
  public Book get(@PathVariable long libraryId, @PathVariable long bookId) {
    Library library service.getLibraryById(libraryId);
    return library.getBookById(bookId);
  }
}

Since I wouldn't take this approach myself, I haven't actually tried this solution! Based on my understanding of Spring, I think it should work though...

Use a polymorphic parent approach.

@Controller
public class CommentsController {
    @RequestMapping(value="/comments", method = RequestMethod.GET)
    public @ResponseBody String index() {
        /* kludge to allow optional path parameters */
        return index(null, null);
    }

    @RequestMapping(value="/{parent_collection}/{parent_id}/comments", method = RequestMethod.GET)
    public @ResponseBody String index(@PathVariable("parent_collection") String parentCollection, @PathVariable("parent_id") String parentId) {
        if (parentCollection == null) {
            return "all comments";
        }
        else if ((parentCollection != null) && (parentCollection.equals("posts"))) {
            /* get parent, then get comments for parent */
            return "comments for single post";
        }
        else if ((parentCollection != null) && (parentCollection.equals("customers"))) {
            /* get parent, then get comments for parent */
            return "comments for single customer";
        }
        else if ((parentCollection != null) && (parentCollection.equals("movies"))) {
            /* get parent, then get comments for parent */
            return "comments for single movie";
        }
    }

    @RequestMapping(value = "/comments/{id}", method = RequestMethod.GET)
    public @ResponseBody String show(@PathVariable Integer id) {
        /* kludge to allow optional path parameters */
        return show(null, null, id);
    }

    @RequestMapping(value = "/{parent_collection}/{parent_id}/comments/{id}", method = RequestMethod.GET)
    public @ResponseBody String show(@PathVariable("parent_collection") String parentCollection, @PathVariable("parent_id") String parentId, @PathVariable Integer id) {
        /* get comment, then get parent from foreign key */

        if (parentCollection == null) {
            return "single comment";
        }
        else if ((parentCollection != null) && (parentCollection.equals("posts"))) {
            return "single comment for single post";
        }
        else if ((parentCollection != null) && (parentCollection.equals("customers"))) {
            return "single comment for single customer";
        }
        else if ((parentCollection != null) && (parentCollection.equals("movies"))) {
            return "single comment for single movie";
        }
    }
}

Additionally, you could use a base controller to route the URI prefix to parent resources (/libraries/{library_id}/../..), add the parent models to the request scope, and then let the regular request mappings handle the rest of the URI to child resources (/../../books/1). I don't have an example of this off-hand.

Side note. Singular nested resources are generally regarded as an antipattern for URI design. A controller should handle its own resources. The most common implementations make the key for the singular nested resource unique, i.e., not dependent on its parent resource. For instance, a database record primary key. However, there are situations where the key might not be unique, such as an ordinal or position value (e.g., book 1, chapter 1, chapter 2), or maybe even a natural key (e.g., book ISBN, person SSN, email address, username, filename).

Example of canonical URIs for nested resources:

• /articles => ArticlesController#index
• /articles/1 => ArticlesController#show
• /articles/1/comments => CommentsController#index
• /articles/1/comments/2 => CommentsController#show (okay, but not preferred)
• /comments/2 => CommentsController#show (preferred)

I don't think it's possible. But you can have the @RequestMapping annotation on the class itself, so it will save you at least some typing.

@Controller
@RequestMapping("/library/{libraryId}")
public class HelloWorldController {

    @RequestMapping(value="/book/{bookId}")
    public ModelAndView helloWorld() {
        ....
    }

}