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Reverse routing is a feature in Pippo that is used to allow you to easily change your URL structure without having to modify all your code.
Why would you want to build URLs instead of hard-coding them into your templates?
One answer is that reversing is often more descriptive than hard-coding the URLs. More importantly, it allows you to change URLs in one go, without having to remember to change URLs all over the place.

If you create a route like (the Controller aproach):

GET("/contacts/{id}", ContactsController.class, "show");

This route will take requests such as /contacts/1 and map it to the show method on the Contacts controller.

Using reverse routing we can create a link to it and pass in any parameters that we have defined. Extra parameters suplied in method Router.uriFor are added as query parameters in the generated link.
Also this method is available as a shortcut in RouteContext.

Map<String, Object> parameters = new HashMap<>();
parameters.put("id", 1);
parameters.put("action", "new"); // extra parameter
String url = routeContext.uriFor(ContactsController.class, "show", parameters);

And now the link created should be something like /contacts/1?action=new.

The same can be applied to non controller routes:

GET("/contacts/{id}", routeContext -> {...}

Now we can use uriFor(String uriPattern, Map<String, Object> parameters) method to retrieves the URL:

Map<String, Object> parameters = new HashMap<>();
parameters.put("id", 1);
parameters.put("action", "new");
String url = routeContext.uriFor("/contacts/{id}", parameters);

Are some scenarios when it's more ease to use the route name for uriFor().
In few words I can add a route (in an hypothetical blog application) that render a template with:

GET("/blogs/{year}/{month}/{day}/{title}", routeContext -> { routeContext.render("myTemplate")});

It's hard to create the reverse routing using the uriPattern:

Map<String, Object> parameters = ...
routeContext.uriFor("/blogs/{year}/{month}/{day}/{title}", parameters);

The simplest solution is to add a name to our route and to use this name when we build the URL(reverse routing) to that route:

GET("/blogs/{year}/{month}/{day}/{title}", routeContext -> routeContext.render("myTemplate")).named("blog");

The new code becomes more short and readable:

Map<String, Object> parameters = ...
routeContext.uriFor("blog", parameters);

Advantages:

  • it is often more descriptive than hard-coding the uriPattern
  • it allows you to change uriPattern in one go, without having to remember to change URLs all over the place.

Note: By default (via DefaultRouter) the uriFor method automatically encode the parameters values.

In conclusion if you want to create links to routes or controllers you must use Router.uriFor methods.