Spring Boot 3 Recipes by 2024

Author:2024
Language: eng
Format: epub

Chapter 4 WebFlux

As the WebClient reuses parts of the same infrastructure as the rest of WebFlux, we can reuse the same exception handling we used earlier. When calling http://

localhost:8090/books/9780618260300 from the command line using curl or HTTPie, you will get output similar to Figure 4-15.

Figure 4-15. Enriched book result

Use a Declarative Client

Spring Framework 6 introduced the declarative HTTP client. With this it is possible to write an interface with some annotations. At runtime a proxy will be created that will handle the request/response including the mapping and exception handling.

The starting point is an interface with an @HttpExchange annotation (or one of the derived annotations like @GetExchange and @PostExchange) on either the class or the method(s). It functions much in the same way as the @RequestMapping annotation from the server API.

Using the @HttpExchange annotation, it is possible to set some properties (see Table 4-9).

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Chapter 4 WebFlux

Table 4-9. HttpExchange Properties

Attribute

Description

value or url

the url for the request; can be a full url, a path relative to the type level

@HttpExchange, or the preset base urI.

Method

the http method to use; DELETE, GET, PATCH, POST, or PUT. the default is

empty.

contentType

the media type to send for the Content-Type header; the default is empty.

Accept

the media type for the Accept header.

In addition to the @HttpExchange annotation, there are @DeleteExchange,

@GetExchange, @PatchExchange, @PostExchange, and @PutExchange annotations.

These can be used instead of @HttpExchange with a specific method value. Using these annotations makes it more explicit.

Just like request handling methods with @RequestMapping, the declarative client supports multiple arguments, annotations, and return types. It reuses common parts of the web infrastructure for this. See Table 4-10.

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Chapter 4 WebFlux

Table 4-10. HttpExchange-Supported Method Arguments

Type

Description

java.net.URI

Dynamically sets the url for the request; overrides the url attribute from

the @HttpExchange.

UriBuilderFactory provides a UriBuilderFactory to expand the urI template and urI variables. used instead of the UriBuilderFactory of the underlying client.

HttpMethod

Dynamically sets the http method to use for the request; overrides the

method attribute from the @HttpExchange.

MultipartFile

adds a request part from a MultipartFile, typically used with Spring

MVC to indicate an uploaded file.

@CookieValue

adds cookies to the outgoing request. the argument can be a Map<String,

?> or a MultiValueMap<String, ?> with multiple cookies or individual

values. uses the type conversion for non-String values.

@RequestHeader

adds request headers to the outgoing request. the argument can be a

Map<String, ?> or a MultiValueMap<String, ?> with multiple

headers or individual values. uses the type conversion for non-String values.

@PathVariable

adds a variable to expand a placeholder in the request url. the argument

can be a Map<String, ?> for multiple values or an individual value.

uses the type conversion for non-String values.

@RequestBody

provides the body of the request either as an Object to be serialized or as

a reactive Streams publisher such as Mono, Flux, or any other async type

supported through the configured ReactiveAdapterRegistry.

@RequestParam

adds request parameters. Can be a Map<String, ?> /

MultiValueMap<String, ?> for multiple values. Or can be an

individual type. uses the type conversion for non-String values. When

contentType is application/x-www-form-urlencoded, the

parameters are added to the request body.

@RequestPart

adds a request part that can be a String (becomes a form field), a

Resource, an Object to be encoded as JSON (or whatever

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