[[mvc-uri-building]]
= URI Links

[.small]#xref:web/webflux/uri-building.adoc[See equivalent in the Reactive stack]#

This section describes various options available in the Spring Framework to work with URI's.

include::partial$web/web-uris.adoc[leveloffset=+1]


[[mvc-servleturicomponentsbuilder]]
== Relative Servlet Requests

You can use `ServletUriComponentsBuilder` to create URIs relative to the current request,
as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	HttpServletRequest request = ...

	// Re-uses scheme, host, port, path, and query string...

	URI uri = ServletUriComponentsBuilder.fromRequest(request)
			.replaceQueryParam("accountId", "{id}")
			.build("123");
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val request: HttpServletRequest = ...

	// Re-uses scheme, host, port, path, and query string...

	val uri = ServletUriComponentsBuilder.fromRequest(request)
			.replaceQueryParam("accountId", "{id}")
			.build("123")
----
======

You can create URIs relative to the context path, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	HttpServletRequest request = ...

	// Re-uses scheme, host, port, and context path...

	URI uri = ServletUriComponentsBuilder.fromContextPath(request)
			.path("/accounts")
			.build()
			.toUri();
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val request: HttpServletRequest = ...

	// Re-uses scheme, host, port, and context path...

	val uri = ServletUriComponentsBuilder.fromContextPath(request)
			.path("/accounts")
			.build()
			.toUri()
----
======

You can create URIs relative to a Servlet (for example, `/main/{asterisk}`),
as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	HttpServletRequest request = ...

	// Re-uses scheme, host, port, context path, and Servlet mapping prefix...

	URI uri = ServletUriComponentsBuilder.fromServletMapping(request)
			.path("/accounts")
			.build()
			.toUri();
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val request: HttpServletRequest = ...

	// Re-uses scheme, host, port, context path, and Servlet mapping prefix...

	val uri = ServletUriComponentsBuilder.fromServletMapping(request)
			.path("/accounts")
			.build()
			.toUri()
----
======

NOTE: As of 5.1, `ServletUriComponentsBuilder` ignores information from the `Forwarded` and
`X-Forwarded-*` headers, which specify the client-originated address. Consider using the
xref:web/webmvc/filters.adoc#filters-forwarded-headers[`ForwardedHeaderFilter`] to extract and use or to discard
such headers.


[[mvc-links-to-controllers]]
== Links to Controllers

Spring MVC provides a mechanism to prepare links to controller methods. For example,
the following MVC controller allows for link creation:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	@Controller
	@RequestMapping("/hotels/{hotel}")
	public class BookingController {

		@GetMapping("/bookings/{booking}")
		public ModelAndView getBooking(@PathVariable Long booking) {
			// ...
		}
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	@Controller
	@RequestMapping("/hotels/{hotel}")
	class BookingController {

		@GetMapping("/bookings/{booking}")
		fun getBooking(@PathVariable booking: Long): ModelAndView {
			// ...
		}
	}
----
======

You can prepare a link by referring to the method by name, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	UriComponents uriComponents = MvcUriComponentsBuilder
		.fromMethodName(BookingController.class, "getBooking", 21).buildAndExpand(42);

	URI uri = uriComponents.encode().toUri();
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val uriComponents = MvcUriComponentsBuilder
		.fromMethodName(BookingController::class.java, "getBooking", 21).buildAndExpand(42)

	val uri = uriComponents.encode().toUri()
----
======

In the preceding example, we provide actual method argument values (in this case, the long value: `21`)
to be used as a path variable and inserted into the URL. Furthermore, we provide the
value, `42`, to fill in any remaining URI variables, such as the `hotel` variable inherited
from the type-level request mapping. If the method had more arguments, we could supply null for
arguments not needed for the URL. In general, only `@PathVariable` and `@RequestParam` arguments
are relevant for constructing the URL.

There are additional ways to use `MvcUriComponentsBuilder`. For example, you can use a technique
akin to mock testing through proxies to avoid referring to the controller method by name, as the following example shows
(the example assumes static import of `MvcUriComponentsBuilder.on`):

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	UriComponents uriComponents = MvcUriComponentsBuilder
		.fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

	URI uri = uriComponents.encode().toUri();
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val uriComponents = MvcUriComponentsBuilder
		.fromMethodCall(on(BookingController::class.java).getBooking(21)).buildAndExpand(42)

	val uri = uriComponents.encode().toUri()
----
======

NOTE: Controller method signatures are limited in their design when they are supposed to be usable for
link creation with `fromMethodCall`. Aside from needing a proper parameter signature,
there is a technical limitation on the return type (namely, generating a runtime proxy
for link builder invocations), so the return type must not be `final`. In particular,
the common `String` return type for view names does not work here. You should use `ModelAndView`
or even plain `Object` (with a `String` return value) instead.

The earlier examples use static methods in `MvcUriComponentsBuilder`. Internally, they rely
on `ServletUriComponentsBuilder` to prepare a base URL from the scheme, host, port,
context path, and servlet path of the current request. This works well in most cases.
However, sometimes, it can be insufficient. For example, you may be outside the context of
a request (such as a batch process that prepares links) or perhaps you need to insert a path
prefix (such as a locale prefix that was removed from the request path and needs to be
re-inserted into links).

For such cases, you can use the static `fromXxx` overloaded methods that accept a
`UriComponentsBuilder` to use a base URL. Alternatively, you can create an instance of `MvcUriComponentsBuilder`
with a base URL and then use the instance-based `withXxx` methods. For example, the
following listing uses `withMethodCall`:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	UriComponentsBuilder base = ServletUriComponentsBuilder.fromCurrentContextPath().path("/en");
	MvcUriComponentsBuilder builder = MvcUriComponentsBuilder.relativeTo(base);
	builder.withMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

	URI uri = uriComponents.encode().toUri();
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	val base = ServletUriComponentsBuilder.fromCurrentContextPath().path("/en")
	val builder = MvcUriComponentsBuilder.relativeTo(base)
	builder.withMethodCall(on(BookingController::class.java).getBooking(21)).buildAndExpand(42)

	val uri = uriComponents.encode().toUri()
----
======

NOTE: As of 5.1, `MvcUriComponentsBuilder` ignores information from the `Forwarded` and
`X-Forwarded-*` headers, which specify the client-originated address. Consider using the
xref:web/webmvc/filters.adoc#filters-forwarded-headers[ForwardedHeaderFilter] to extract and use or to discard
such headers.


[[mvc-links-to-controllers-from-views]]
== Links in Views

In views such as Thymeleaf, FreeMarker, or JSP, you can build links to annotated controllers
by referring to the implicitly or explicitly assigned name for each request mapping.

Consider the following example:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	@RequestMapping("/people/{id}/addresses")
	public class PersonAddressController {

		@RequestMapping("/{country}")
		public HttpEntity<PersonAddress> getAddress(@PathVariable String country) { ... }
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	@RequestMapping("/people/{id}/addresses")
	class PersonAddressController {

		@RequestMapping("/{country}")
		fun getAddress(@PathVariable country: String): HttpEntity<PersonAddress> { ... }
	}
----
======

Given the preceding controller, you can prepare a link from a JSP, as follows:

[source,jsp,indent=0,subs="verbatim,quotes"]
----
<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %>
...
<a href="${s:mvcUrl('PAC#getAddress').arg(0,'US').buildAndExpand('123')}">Get Address</a>
----

The preceding example relies on the `mvcUrl` function declared in the Spring tag library
(that is, META-INF/spring.tld), but it is easy to define your own function or prepare a
similar one for other templating technologies.

Here is how this works. On startup, every `@RequestMapping` is assigned a default name
through `HandlerMethodMappingNamingStrategy`, whose default implementation uses the
capital letters of the class and the method name (for example, the `getThing` method in
`ThingController` becomes "TC#getThing"). If there is a name clash, you can use
`@RequestMapping(name="..")` to assign an explicit name or implement your own
`HandlerMethodMappingNamingStrategy`.
