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UriComponents

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

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.

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

URI 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:

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

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

URI 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:

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

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

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

The following example configures a WebClient:

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

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

WebClient 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:

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

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

URI Encoding

Spring MVC and Spring WebFlux

UriComponentsBuilder exposes encoding options at two levels:

  • {api-spring-framework}/web/util/UriComponentsBuilder.html#encode--[UriComponentsBuilder#encode()]: Pre-encodes the URI template first and then strictly encodes URI variables when expanded.

  • {api-spring-framework}/web/util/UriComponents.html#encode--[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.

Tip
 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 option 2 is useful only if URI variables intentionally contain reserved characters.

The following example uses the first option:

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"

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

URI 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:

URI uri = UriComponentsBuilder.fromPath("/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:

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();

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#encodeUriUriVariables prior to expanding them into the template.

  • URI_COMPONENTS: 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_COMPONENTS for historic reasons and for backwards compatibility. The WebClient relies on the default value in DefaultUriBuilderFactory, which was changed from EncodingMode.URI_COMPONENTS in 5.0.x to EncodingMode.TEMPLATE_AND_VALUES in 5.1.