This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.2.0!

URI Links

See equivalent in the Servlet stack

This section describes various options available in the Spring Framework to prepare URIs.

UriComponents

Spring MVC and Spring WebFlux

UriComponentsBuilder helps to build URI’s from URI templates with variables, as the following example shows:

Java
Kotlin

UriComponents uriComponents = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}") (1)
		.queryParam("q", "{q}") (2)
		.encode() (3)
		.build(); (4)

URI uri = uriComponents.expand("Westin", "123").toUri(); (5)

1	Static factory method with a URI template.
2	Add or replace URI components.
3	Request to have the URI template and URI variables encoded.
4	Build a `UriComponents`.
5	Expand variables and obtain the `URI`.

val uriComponents = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}") (1)
		.queryParam("q", "{q}") (2)
		.encode() (3)
		.build() (4)

val uri = uriComponents.expand("Westin", "123").toUri() (5)

1	Static factory method with a URI template.
2	Add or replace URI components.
3	Request to have the URI template and URI variables encoded.
4	Build a `UriComponents`.
5	Expand variables and obtain the `URI`.

The preceding example can be consolidated into one chain and shortened with buildAndExpand, as the following example shows:

Java
Kotlin

URI uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}")
		.queryParam("q", "{q}")
		.encode()
		.buildAndExpand("Westin", "123")
		.toUri();

val uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}")
		.queryParam("q", "{q}")
		.encode()
		.buildAndExpand("Westin", "123")
		.toUri()

You can shorten it further by going directly to a URI (which implies encoding), as the following example shows:

Java
Kotlin

URI uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}")
		.queryParam("q", "{q}")
		.build("Westin", "123");

val uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}")
		.queryParam("q", "{q}")
		.build("Westin", "123")

You can shorten it further still with a full URI template, as the following example shows:

Java
Kotlin

URI uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}?q={q}")
		.build("Westin", "123");

val uri = UriComponentsBuilder
		.fromUriString("https://example.com/hotels/{hotel}?q={q}")
		.build("Westin", "123")

UriBuilder

Spring MVC and Spring WebFlux

UriComponentsBuilder implements UriBuilder. You can create a UriBuilder, in turn, with a UriBuilderFactory. Together, UriBuilderFactory and UriBuilder provide a pluggable mechanism to build URIs from URI templates, based on shared configuration, such as a base URL, encoding preferences, and other details.

You can configure RestTemplate and WebClient with a UriBuilderFactory to customize the preparation of URIs. DefaultUriBuilderFactory is a default implementation of UriBuilderFactory that uses UriComponentsBuilder internally and exposes shared configuration options.

The following example shows how to configure a RestTemplate:

Java
Kotlin

// import org.springframework.web.util.DefaultUriBuilderFactory.EncodingMode;

String baseUrl = "https://example.org";
DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory(baseUrl);
factory.setEncodingMode(EncodingMode.TEMPLATE_AND_VALUES);

RestTemplate restTemplate = new RestTemplate();
restTemplate.setUriTemplateHandler(factory);

// import org.springframework.web.util.DefaultUriBuilderFactory.EncodingMode

val baseUrl = "https://example.org"
val factory = DefaultUriBuilderFactory(baseUrl)
factory.encodingMode = EncodingMode.TEMPLATE_AND_VALUES

val restTemplate = RestTemplate()
restTemplate.uriTemplateHandler = factory

The following example configures a WebClient:

Java
Kotlin

// import org.springframework.web.util.DefaultUriBuilderFactory.EncodingMode;

String baseUrl = "https://example.org";
DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory(baseUrl);
factory.setEncodingMode(EncodingMode.TEMPLATE_AND_VALUES);

WebClient client = WebClient.builder().uriBuilderFactory(factory).build();

// import org.springframework.web.util.DefaultUriBuilderFactory.EncodingMode

val baseUrl = "https://example.org"
val factory = DefaultUriBuilderFactory(baseUrl)
factory.encodingMode = EncodingMode.TEMPLATE_AND_VALUES

val client = WebClient.builder().uriBuilderFactory(factory).build()

In addition, you can also use DefaultUriBuilderFactory directly. It is similar to using UriComponentsBuilder but, instead of static factory methods, it is an actual instance that holds configuration and preferences, as the following example shows:

Java
Kotlin

String baseUrl = "https://example.com";
DefaultUriBuilderFactory uriBuilderFactory = new DefaultUriBuilderFactory(baseUrl);

URI uri = uriBuilderFactory.uriString("/hotels/{hotel}")
		.queryParam("q", "{q}")
		.build("Westin", "123");

val baseUrl = "https://example.com"
val uriBuilderFactory = DefaultUriBuilderFactory(baseUrl)

val uri = uriBuilderFactory.uriString("/hotels/{hotel}")
		.queryParam("q", "{q}")
		.build("Westin", "123")

URI Parsing

Spring MVC and Spring WebFlux

UriComponentsBuilder supports two URI parser types:

RFC parser — this parser type expects URI strings to conform to RFC 3986 syntax, and treats deviations from the syntax as illegal.
WhatWG parser — this parser is based on the URL parsing algorithm in the WhatWG URL Living standard. It provides lenient handling of a wide range of cases of unexpected input. Browsers implement this in order to handle leniently user typed URL’s. For more details, see the URL Living Standard and URL parsing test cases.

By default, RestClient, WebClient, and RestTemplate use the RFC parser type, and expect applications to provide with URL templates that conform to RFC syntax. To change that you can customize the UriBuilderFactory on any of the clients.

Applications and frameworks may further rely on UriComponentsBuilder for their own needs to parse user provided URL’s in order to inspect and possibly validated URI components such as the scheme, host, port, path, and query. Such components can decide to use the WhatWG parser type in order to handle URL’s more leniently, and to align with the way browsers parse URI’s, in case of a redirect to the input URL or if it is included in a response to a browser.

URI Encoding

Spring MVC and Spring WebFlux

UriComponentsBuilder exposes encoding options at two levels:

UriComponentsBuilder#encode(): Pre-encodes the URI template first and then strictly encodes URI variables when expanded.
UriComponents#encode(): Encodes URI components after URI variables are expanded.

Both options replace non-ASCII and illegal characters with escaped octets. However, the first option also replaces characters with reserved meaning that appear in URI variables.

Consider ";", which is legal in a path but has reserved meaning. The first option replaces ";" with "%3B" in URI variables but not in the URI template. By contrast, the second option never replaces ";", since it is a legal character in a path.

For most cases, the first option is likely to give the expected result, because it treats URI variables as opaque data to be fully encoded, while the second option is useful if URI variables do intentionally contain reserved characters. The second option is also useful when not expanding URI variables at all since that will also encode anything that incidentally looks like a URI variable.

The following example uses the first option:

Java
Kotlin

URI uri = UriComponentsBuilder.fromPath("/hotel list/{city}")
		.queryParam("q", "{q}")
		.encode()
		.buildAndExpand("New York", "foo+bar")
		.toUri();

// Result is "/hotel%20list/New%20York?q=foo%2Bbar"

val uri = UriComponentsBuilder.fromPath("/hotel list/{city}")
		.queryParam("q", "{q}")
		.encode()
		.buildAndExpand("New York", "foo+bar")
		.toUri()

// Result is "/hotel%20list/New%20York?q=foo%2Bbar"

You can shorten the preceding example by going directly to the URI (which implies encoding), as the following example shows:

Java
Kotlin

URI uri = UriComponentsBuilder.fromPath("/hotel list/{city}")
		.queryParam("q", "{q}")
		.build("New York", "foo+bar");

val uri = UriComponentsBuilder.fromPath("/hotel list/{city}")
		.queryParam("q", "{q}")
		.build("New York", "foo+bar")

You can shorten it further still with a full URI template, as the following example shows:

Java
Kotlin

URI uri = UriComponentsBuilder.fromUriString("/hotel list/{city}?q={q}")
		.build("New York", "foo+bar");

val uri = UriComponentsBuilder.fromUriString("/hotel list/{city}?q={q}")
		.build("New York", "foo+bar")

The WebClient and the RestTemplate expand and encode URI templates internally through the UriBuilderFactory strategy. Both can be configured with a custom strategy, as the following example shows:

Java
Kotlin

String baseUrl = "https://example.com";
DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory(baseUrl)
factory.setEncodingMode(EncodingMode.TEMPLATE_AND_VALUES);

// Customize the RestTemplate..
RestTemplate restTemplate = new RestTemplate();
restTemplate.setUriTemplateHandler(factory);

// Customize the WebClient..
WebClient client = WebClient.builder().uriBuilderFactory(factory).build();

val baseUrl = "https://example.com"
val factory = DefaultUriBuilderFactory(baseUrl).apply {
	encodingMode = EncodingMode.TEMPLATE_AND_VALUES
}

// Customize the RestTemplate..
val restTemplate = RestTemplate().apply {
	uriTemplateHandler = factory
}

// Customize the WebClient..
val client = WebClient.builder().uriBuilderFactory(factory).build()

The DefaultUriBuilderFactory implementation uses UriComponentsBuilder internally to expand and encode URI templates. As a factory, it provides a single place to configure the approach to encoding, based on one of the below encoding modes:

TEMPLATE_AND_VALUES: Uses UriComponentsBuilder#encode(), corresponding to the first option in the earlier list, to pre-encode the URI template and strictly encode URI variables when expanded.
VALUES_ONLY: Does not encode the URI template and, instead, applies strict encoding to URI variables through UriUtils#encodeUriVariables prior to expanding them into the template.
URI_COMPONENT: Uses UriComponents#encode(), corresponding to the second option in the earlier list, to encode URI component value after URI variables are expanded.
NONE: No encoding is applied.

The RestTemplate is set to EncodingMode.URI_COMPONENT for historical reasons and for backwards compatibility. The WebClient relies on the default value in DefaultUriBuilderFactory, which was changed from EncodingMode.URI_COMPONENT in 5.0.x to EncodingMode.TEMPLATE_AND_VALUES in 5.1.