URI Links

This section describes various options available in the TODAY Framework to work with URI’s.

UriComponents

Web MVC and Infra WebFlux

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

Java

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:

Java

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:

Java

URI 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

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

UriBuilder

Web MVC and Infra 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

// import cn.taketoday.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);

The following example configures a WebClient:

Java

// import cn.taketoday.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();

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

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

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

URI Encoding

Web MVC and Infra 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

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:

Java

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:

Java

URI 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

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#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 historic 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.

Relative Servlet Requests

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

HttpServletRequest request = ...

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

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

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

HttpServletRequest request = ...

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

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

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

Java

HttpServletRequest request = ...

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

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

Links to Controllers

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

Java

@Controller
@RequestMapping("/hotels/{hotel}")
public class BookingController {

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

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

Java

UriComponents uriComponents = MvcUriComponentsBuilder
  .fromMethodName(BookingController.class, "getBooking", 21).buildAndExpand(42);

URI 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):

Java

UriComponents uriComponents = MvcUriComponentsBuilder
  .fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);

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

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 mockApi 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:

Java

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();

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:

Java

@RequestMapping("/people/{id}/addresses")
public class PersonAddressController {

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

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

<%@ 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 Infra 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.