Allow links to @Controller methods from views without hardcoding URLs [SPR-5779]

[spring-projects-issues]

Chris Herron opened SPR-5779 and commented

The various Spring Web tags and template-URI implementation encourage hard-coding of URLs in the view layer.
If I alter a Controller's URL mapping, I need to remember to go and make the corresponding change(s) in my JSPs so that links and forms aren't broken.
If the spring:url and form:form tags were able to accept the FQCN of a controller bean instead of an actual URL, the tag implementation could determine the most appropriate URL mapping, and (if applicable) incorporate any template-URI params / path variables to generate a reliable URL.
By using the the FQCN, we can rely on any modern IDE to locate references during refactoring, instead of requiring additional help from Spring-aware IDE plugins. IMHO this would fit particularly well with Spring 3.0's annotation-based controller configuration.

Stripes supports this approach:
http://stripes.sourceforge.net/docs/current/taglib/stripes/link.html
http://stripes.sourceforge.net/docs/current/taglib/stripes/form.html

---

Affects: 3.0 M3

Reference URL: http://forum.springsource.org/showthread.php?t=72284

Issue Links:

• URI/URL Related Improvement Suggestions for RequestMapping in Spring MVC [SPR-7585] #12241 URI/URL Related Improvement Suggestions for RequestMapping in Spring MVC ("is duplicated by")
• Externalized request mapping as a 1st class alternative to @RequestMapping [SPR-5757] #10427 Externalized request mapping as a 1st class alternative to @RequestMapping
• Form tag should prepend the contextPath and servletPath if not present [SPR-8684] #13326 Form tag should prepend the contextPath and servletPath if not present

Referenced from: commits 6b129c5, 9d479fe

32 votes, 29 watchers

[spring-projects-issues]

Chris Herron commented

Oops - meant to say "If the spring:url and form:form tags" in the original description.

[spring-projects-issues]

Dave Syer commented

Fixed the description.

The problem I see is that "determine the most appropriate URL mapping" isn't particularly well posed. How would a JSP tag know which of potentially many URLs were intended? Only really makes sense if there is a way to specify the particular @RequestMapping (except in the special case where a single controller has a single mapping - old style interface driven MVC). I suppose that's what you had in mind?

[spring-projects-issues]

Chris Herron commented

Yes - ideally we could specify both the classname and the targeted method. Then the corresponding @RequestMapping could be identified. You might do this with one or two tag parameters:

<spring:url class="com.foo.UserProfileController" method="view">
   <spring:param name="user.username" value="${user.username}" />
</spring:url>

or

<spring:url target="com.foo.UserProfileController#view" >
   <spring:param name="user.username" value="${user.username}" />
</spring:url>

The equivalent in Stripes:

@UrlBinding("/profile/{$event}/{user.username}/")
public class UserProfileController {
    private User user;
    public Resolution view() { ... );
    public User getUser() { ... };
    public void setUser(User user) { ... };
}

<stripes:link beanclass="com.foo.UserProfileController" event="view">
   <stripes:param name="user.username" value="${user.username}"/>
</stripes:link>

This generates a URL like: http://foo.com/profile/view/johnsmith.

[spring-projects-issues]

Numan Salati commented

+1

grails does this with g:link tag. very useful functionality to have. i am surprised this feature is missing since its a common feature on many web frameworks.

please implement this.

[spring-projects-issues]

Elnur Abdurrakhimov commented

I'd really like to have this functionality. Any progress on this? Or maybe any pointers to existing solutions solving this problem?

[spring-projects-issues]

Elnur Abdurrakhimov commented

I'm trying to switch from the PHP Spring's clone Symfony2 to Spring, because I like Java much more than PHP. Since Symfony2 is a Spring's clone, I thought I'd share a couple of links to its implementation of routes in hope it will help to solve this problem in Spring too. So, here we go:

• http://symfony.com/doc/current/book/routing.html
• http://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/routing.html

[spring-projects-issues]

Rossen Stoyanchev commented

Thanks for the links. We're considering some sort of a centralized route mapping configuration for 3.2. This certainly provides a good example including the ability to refer to a specific mapping through an alias.

[spring-projects-issues]

Jari Pennanen commented

Has anyone a idea how to implement this as an JAR?

It sounds like a simple thing to do, I need a way to create Map of all controllers and their Request mappings. (Assuming each controller has at maximum one RequestMapping it is easy, otherwise RequestMappings must be named too).

I've been using Django in the past also a lot. But been yearning for "strongly typed Django", so I seeked for Spring. This would be a killer feature as it would allow to create:

1. Project specific RequestMappings.
2. (optionally) Site widely overriding the RequestMapping of certain controllers.

And the urls would just keep working.

[spring-projects-issues]

Brian Clozel commented

I've had the same problem and came up with another solution: https://github.com/bclozel/springmvc-router

[spring-projects-issues]

Jari Pennanen commented

Brian, that's fantastic! And it works today.

Is the package name part of the reversing?

I'm looking at the code:
${route.reverse('userController.listAll')}

Can I do like this instead:
${route.reverse('mypackage.userController.listAll')}

If have several apps, like "Auth" app in a different WAR. Can I reverse it from my other application using ${route.reverse(otherpackage.Auth.AuthController.login)} ? As I'd like to separate all apps, but still being able to access their urls and functions somehow.

[spring-projects-issues]

Brian Clozel commented

Currently the controller name "userController" is based on the bean name created by Spring. I don't know how Spring handles naming when several Controllers have the same classname.

But I guess you can go:

@Controller("auth.MyController") on one,
@Controller("business.MyController") on another one.

[spring-projects-issues]

Brian Clozel commented

Not sure about a "." in a controller bean name: I think it's used as a separator in "controllerName.action".

Maybe?
@Controller("auth-MyController")
@Controller("business-MyController")

[spring-projects-issues]

Rossen Stoyanchev commented

Chris Herron, since @RequestMapping annotations are both type and method level, a method name at least must be specified. That won't work in the general case since method names can be overloaded. Furthermore each annotation can have multiple URL patterns and patterns can contain Ant-style wild cards (e.g. "/foo/\*", "/foo\*Bar", /foo/\*\*/bar"). All of these are challenges for reverse engineering in the general case. However, to make this work some assumptions could be made -- e.g. the method must not be overloaded, the annotation must have only one URL pattern, and the URL pattern must not have any wild cards.

Overall I think the approach would work, if anyone wants to put something together in the form of a pull request. Specific questions, if any, can be posted to the spring-framework-contrib list. I do think this should be a different tag ("spring:requestMappingUrl", "spring:controllerUrl" maybe?) even if internally the UrlTag class is extended.

The springmvc-router project looks very nice also as an alternative to @RequestMapping annotations!

[spring-projects-issues]

Alexander Hawley commented

Asp.Net implementation might be workable.

Many MVC frameworks generate URIs from controller mappings. It closes the loop on referencing a controller action from anywhere: a redirect from controller to controller, link from a view to controller, submit form from view to controller. They can all reference the resource map in the same way.

[spring-projects-issues]

Andy Chang commented

We have been using a form of this internally @ mohchi.com, but it requires a separate annotation (@Action). It supports path variables but perhaps not in the way you'd like it to. It uses an action uri builder to build urls in the view layer. I hope that some elements from our example might help in integrating this functionality into spring:url and @RequestMapping.

The controller:
https://github.com/mohchi/spring-mvc-action-resolver/blob/master/src/main/java/com/mohchi/example/web/controllers/HomePageController.java

The jsp:
https://github.com/mohchi/spring-mvc-action-resolver/blob/master/src/main/webapp/WEB-INF/views/homePage.jsp

That the JSP doesn't have any examples of this, but it also supports fully qualified names, e.g. "com.mohchi.example.web.controller.HomePageController#homePage". However, one limitation is that it doesn't support overloaded controller methods annotated with @Action.

[spring-projects-issues]

Fabien benichou commented

It is à shame that such a popular MVC framework like Spring does not have this mechanism present in many other frameworks (like Grails) and forces you to hardcode your URLs in your code

Why this feature is not a top priority for future releases ?

[spring-projects-issues]

Juergen Hoeller commented

Let's put this into the 4.1 bucket to consider potential mechanisms in Spring MVC itself, or at least some enablers for custom policies to be implemented on top of it.

Juergen

[spring-projects-issues]

Rossen Stoyanchev commented

Now that we have MvcUriComponentsBuilder, this is a good one to consider. For example based on the fromMethodName method.

[spring-projects-issues]

Rossen Stoyanchev commented

I've created a proposal to address this. For anyone interested, you can try it with 4.1.0.BUILD-SNAPSHOT (repo.spring.io/snapshot).

For an overview and sample usage, see the javadoc of MvcUriComponentsBuilder.fromMappingName.

[spring-projects-issues]

Rossen Stoyanchev commented

Modified title (was "Add "controller class name" attribute to spring:url and form:form tags")