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/*
 * Copyright 2002-2023 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.client;

import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;
import java.nio.charset.Charset;
import java.time.ZonedDateTime;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;

import io.micrometer.observation.ObservationRegistry;

import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpRequest;
import org.springframework.http.HttpStatusCode;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.StreamingHttpOutputMessage;
import org.springframework.http.client.ClientHttpRequest;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.ClientHttpRequestInitializer;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.observation.ClientRequestObservationConvention;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.web.util.DefaultUriBuilderFactory;
import org.springframework.web.util.UriBuilder;
import org.springframework.web.util.UriBuilderFactory;

/**
 * Client to perform HTTP requests, exposing a fluent, synchronous API over
 * underlying HTTP client libraries such as the JDK {@code HttpClient}, Apache
 * HttpComponents, and others.
 *
 * 

Use static factory methods {@link #create()}, {@link #create(String)}, * or {@link RestClient#builder()} to prepare an instance. To use the same * configuration as a {@link RestTemplate}, use {@link #create(RestTemplate)} or * {@link #builder(RestTemplate)}. * *

For examples with a response body see: *

    *
  • {@link RequestHeadersSpec#retrieve() retrieve()} *
  • {@link RequestHeadersSpec#exchange(RequestHeadersSpec.ExchangeFunction) exchange(Function<ClientHttpRequest, T>)} *
* *

For examples with a request body see: *

    *
  • {@link RequestBodySpec#body(Object) body(Object)} *
  • {@link RequestBodySpec#body(Object, ParameterizedTypeReference) body(Object, ParameterizedTypeReference)} *
  • {@link RequestBodySpec#body(StreamingHttpOutputMessage.Body) body(Consumer<OutputStream>)} *
* * @author Arjen Poutsma * @since 6.1 */ public interface RestClient { /** * Start building an HTTP GET request. * @return a spec for specifying the target URL */ RequestHeadersUriSpec get(); /** * Start building an HTTP HEAD request. * @return a spec for specifying the target URL */ RequestHeadersUriSpec head(); /** * Start building an HTTP POST request. * @return a spec for specifying the target URL */ RequestBodyUriSpec post(); /** * Start building an HTTP PUT request. * @return a spec for specifying the target URL */ RequestBodyUriSpec put(); /** * Start building an HTTP PATCH request. * @return a spec for specifying the target URL */ RequestBodyUriSpec patch(); /** * Start building an HTTP DELETE request. * @return a spec for specifying the target URL */ RequestHeadersUriSpec delete(); /** * Start building an HTTP OPTIONS request. * @return a spec for specifying the target URL */ RequestHeadersUriSpec options(); /** * Start building a request for the given {@code HttpMethod}. * @return a spec for specifying the target URL */ RequestBodyUriSpec method(HttpMethod method); /** * Return a builder to create a new {@code RestClient} whose settings are * replicated from this {@code RestClient}. */ Builder mutate(); // Static factory methods /** * Create a new {@code RestClient}. * @see #create(String) * @see #builder() */ static RestClient create() { return new DefaultRestClientBuilder().build(); } /** * Variant of {@link #create()} that accepts a default base URL. For more * details see {@link Builder#baseUrl(String) Builder.baseUrl(String)}. * @param baseUrl the base URI for all requests * @see #builder() */ static RestClient create(String baseUrl) { return new DefaultRestClientBuilder().baseUrl(baseUrl).build(); } /** * Create a new {@code RestClient} based on the configuration of the * given {@code RestTemplate}. The returned builder is configured with the * template's *
    *
  • {@link RestTemplate#getRequestFactory() ClientHttpRequestFactory},
  • *
  • {@link RestTemplate#getMessageConverters() HttpMessageConverters},
  • *
  • {@link RestTemplate#getInterceptors() ClientHttpRequestInterceptors},
  • *
  • {@link RestTemplate#getClientHttpRequestInitializers() ClientHttpRequestInitializers},
  • *
  • {@link RestTemplate#getUriTemplateHandler() UriBuilderFactory}, and
  • *
  • {@linkplain RestTemplate#getErrorHandler() error handler}.
  • *
* @param restTemplate the rest template to base the returned client's * configuration on * @return a {@code RestClient} initialized with the {@code restTemplate}'s * configuration */ static RestClient create(RestTemplate restTemplate) { return new DefaultRestClientBuilder(restTemplate).build(); } /** * Obtain a {@code RestClient} builder. */ static RestClient.Builder builder() { return new DefaultRestClientBuilder(); } /** * Obtain a {@code RestClient} builder based on the configuration of the * given {@code RestTemplate}. The returned builder is configured with the * template's *
    *
  • {@link RestTemplate#getRequestFactory() ClientHttpRequestFactory},
  • *
  • {@link RestTemplate#getMessageConverters() HttpMessageConverters},
  • *
  • {@link RestTemplate#getInterceptors() ClientHttpRequestInterceptors},
  • *
  • {@link RestTemplate#getClientHttpRequestInitializers() ClientHttpRequestInitializers},
  • *
  • {@link RestTemplate#getUriTemplateHandler() UriBuilderFactory}, and
  • *
  • {@linkplain RestTemplate#getErrorHandler() error handler}.
  • *
* @param restTemplate the rest template to base the returned builder's * configuration on * @return a {@code RestClient} builder initialized with {@code restTemplate}'s * configuration */ static RestClient.Builder builder(RestTemplate restTemplate) { return new DefaultRestClientBuilder(restTemplate); } /** * A mutable builder for creating a {@link RestClient}. */ interface Builder { /** * Configure a base URL for requests. Effectively a shortcut for: *
		 * String baseUrl = "https://abc.go.com/v1";
		 * DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory(baseUrl);
		 * RestClient client = RestClient.builder().uriBuilderFactory(factory).build();
		 * 
*

The {@code DefaultUriBuilderFactory} is used to prepare the URL * for every request with the given base URL, unless the URL request * for a given URL is absolute in which case the base URL is ignored. *

Note: this method is mutually exclusive with * {@link #uriBuilderFactory(UriBuilderFactory)}. If both are used, the * {@code baseUrl} value provided here will be ignored. * @return this builder * @see DefaultUriBuilderFactory#DefaultUriBuilderFactory(String) * @see #uriBuilderFactory(UriBuilderFactory) */ Builder baseUrl(String baseUrl); /** * Configure default URL variable values to use when expanding URI * templates with a {@link Map}. Effectively a shortcut for: *

		 * Map<String, ?> defaultVars = ...;
		 * DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory();
		 * factory.setDefaultVariables(defaultVars);
		 * RestClient client = RestClient.builder().uriBuilderFactory(factory).build();
		 * 
*

Note: this method is mutually exclusive with * {@link #uriBuilderFactory(UriBuilderFactory)}. If both are used, the * {@code defaultUriVariables} value provided here will be ignored. * @return this builder * @see DefaultUriBuilderFactory#setDefaultUriVariables(Map) * @see #uriBuilderFactory(UriBuilderFactory) */ Builder defaultUriVariables(Map defaultUriVariables); /** * Provide a pre-configured {@link UriBuilderFactory} instance. This is * an alternative to, and effectively overrides the following shortcut * properties: *

    *
  • {@link #baseUrl(String)} *
  • {@link #defaultUriVariables(Map)}. *
* @param uriBuilderFactory the URI builder factory to use * @return this builder * @see #baseUrl(String) * @see #defaultUriVariables(Map) */ Builder uriBuilderFactory(UriBuilderFactory uriBuilderFactory); /** * Global option to specify a header to be added to every request, * if the request does not already contain such a header. * @param header the header name * @param values the header values * @return this builder */ Builder defaultHeader(String header, String... values); /** * Provide a consumer to access to every {@linkplain #defaultHeader(String, String...) * default header} declared so far, with the possibility to add, replace, or remove. * @param headersConsumer the consumer * @return this builder */ Builder defaultHeaders(Consumer headersConsumer); /** * Provide a consumer to customize every request being built. * @param defaultRequest the consumer to use for modifying requests * @return this builder */ Builder defaultRequest(Consumer> defaultRequest); /** * Register a default * {@linkplain ResponseSpec#onStatus(Predicate, ResponseSpec.ErrorHandler) status handler} * to apply to every response. Such default handlers are applied in the * order in which they are registered, and after any others that are * registered for a specific response. * @param statusPredicate to match responses with * @param errorHandler handler that typically, though not necessarily, * throws an exception * @return this builder */ Builder defaultStatusHandler(Predicate statusPredicate, ResponseSpec.ErrorHandler errorHandler); /** * Register a default * {@linkplain ResponseSpec#onStatus(ResponseErrorHandler) status handler} * to apply to every response. Such default handlers are applied in the * order in which they are registered, and after any others that are * registered for a specific response. * @param errorHandler handler that typically, though not necessarily, * throws an exception * @return this builder */ Builder defaultStatusHandler(ResponseErrorHandler errorHandler); /** * Add the given request interceptor to the end of the interceptor chain. * @param interceptor the interceptor to be added to the chain * @return this builder */ Builder requestInterceptor(ClientHttpRequestInterceptor interceptor); /** * Manipulate the interceptors with the given consumer. The list provided to * the consumer is "live", so that the consumer can be used to remove * interceptors, change ordering, etc. * @param interceptorsConsumer a function that consumes the interceptors list * @return this builder */ Builder requestInterceptors(Consumer> interceptorsConsumer); /** * Add the given request initializer to the end of the initializer chain. * @param initializer the initializer to be added to the chain * @return this builder */ Builder requestInitializer(ClientHttpRequestInitializer initializer); /** * Manipulate the initializers with the given consumer. The list provided to * the consumer is "live", so that the consumer can be used to remove * initializers, change ordering, etc. * @param initializersConsumer a function that consumes the initializers list * @return this builder */ Builder requestInitializers(Consumer> initializersConsumer); /** * Configure the {@link ClientHttpRequestFactory} to use. This is useful * for plugging in and/or customizing options of the underlying HTTP * client library (e.g. SSL). *

If no request factory is specified, {@code RestClient} uses * {@linkplain org.springframework.http.client.HttpComponentsClientHttpRequestFactory Apache Http Client}, * {@linkplain org.springframework.http.client.JettyClientHttpRequestFactory Jetty Http Client} * if available on the classpath, and defaults to the * {@linkplain org.springframework.http.client.JdkClientHttpRequestFactory JDK HttpClient} * if the {@code java.net.http} module is loaded, or to a * {@linkplain org.springframework.http.client.SimpleClientHttpRequestFactory simple default} * otherwise. * @param requestFactory the request factory to use * @return this builder */ Builder requestFactory(ClientHttpRequestFactory requestFactory); /** * Configure the message converters for the {@code RestClient} to use. * @param configurer the configurer to apply * @return this builder */ Builder messageConverters(Consumer>> configurer); /** * Configure the {@link io.micrometer.observation.ObservationRegistry} to use * for recording HTTP client observations. * @param observationRegistry the observation registry to use * @return this builder */ Builder observationRegistry(ObservationRegistry observationRegistry); /** * Configure the {@link io.micrometer.observation.ObservationConvention} to use * for collecting metadata for the request observation. Will use * {@link org.springframework.http.client.observation.DefaultClientRequestObservationConvention} * if none provided. * @param observationConvention the observation convention to use * @return this builder */ Builder observationConvention(ClientRequestObservationConvention observationConvention); /** * Apply the given {@code Consumer} to this builder instance. *

This can be useful for applying pre-packaged customizations. * @param builderConsumer the consumer to apply * @return this builder */ Builder apply(Consumer builderConsumer); /** * Clone this {@code RestClient.Builder}. */ Builder clone(); /** * Build the {@link RestClient} instance. */ RestClient build(); } /** * Contract for specifying the URI for a request. * @param a self reference to the spec type */ interface UriSpec> { /** * Specify the URI using an absolute, fully constructed {@link URI}. */ S uri(URI uri); /** * Specify the URI for the request using a URI template and URI variables. *

If a {@link UriBuilderFactory} was configured for the client (e.g. * with a base URI) it will be used to expand the URI template. */ S uri(String uri, Object... uriVariables); /** * Specify the URI for the request using a URI template and URI variables. *

If a {@link UriBuilderFactory} was configured for the client (e.g. * with a base URI) it will be used to expand the URI template. */ S uri(String uri, Map uriVariables); /** * Specify the URI starting with a URI template and finishing off with a * {@link UriBuilder} created from the template. */ S uri(String uri, Function uriFunction); /** * Specify the URI by through a {@link UriBuilder}. * @see #uri(String, Function) */ S uri(Function uriFunction); } /** * Contract for specifying request headers leading up to the exchange. * @param a self reference to the spec type */ interface RequestHeadersSpec> { /** * Set the list of acceptable {@linkplain MediaType media types}, as * specified by the {@code Accept} header. * @param acceptableMediaTypes the acceptable media types * @return this builder */ S accept(MediaType... acceptableMediaTypes); /** * Set the list of acceptable {@linkplain Charset charsets}, as specified * by the {@code Accept-Charset} header. * @param acceptableCharsets the acceptable charsets * @return this builder */ S acceptCharset(Charset... acceptableCharsets); /** * Set the value of the {@code If-Modified-Since} header. * @param ifModifiedSince the new value of the header * @return this builder */ S ifModifiedSince(ZonedDateTime ifModifiedSince); /** * Set the values of the {@code If-None-Match} header. * @param ifNoneMatches the new value of the header * @return this builder */ S ifNoneMatch(String... ifNoneMatches); /** * Add the given, single header value under the given name. * @param headerName the header name * @param headerValues the header value(s) * @return this builder */ S header(String headerName, String... headerValues); /** * Provides access to every header declared so far with the possibility * to add, replace, or remove values. * @param headersConsumer the consumer to provide access to * @return this builder */ S headers(Consumer headersConsumer); /** * Callback for access to the {@link ClientHttpRequest} that in turn * provides access to the native request of the underlying HTTP library. *

This could be useful for setting advanced, per-request options that * are exposed by the underlying library. * @param requestConsumer a consumer to access the * {@code ClientHttpRequest} with * @return this builder */ S httpRequest(Consumer requestConsumer); /** * Proceed to declare how to extract the response. For example to extract * a {@link ResponseEntity} with status, headers, and body: *

		 * ResponseEntity<Person> entity = client.get()
		 *     .uri("/persons/1")
		 *     .accept(MediaType.APPLICATION_JSON)
		 *     .retrieve()
		 *     .toEntity(Person.class);
		 * 
*

Or if interested only in the body: *

		 * Person person = client.get()
		 *     .uri("/persons/1")
		 *     .accept(MediaType.APPLICATION_JSON)
		 *     .retrieve()
		 *     .body(Person.class);
		 * 
*

By default, 4xx response code result in a * {@link HttpClientErrorException} and 5xx response codes in a * {@link HttpServerErrorException}. To customize error handling, use * {@link ResponseSpec#onStatus(Predicate, ResponseSpec.ErrorHandler) onStatus} handlers. * @return {@code ResponseSpec} to specify how to decode the body */ ResponseSpec retrieve(); /** * Exchange the {@link ClientHttpResponse} for a type {@code T}. This * can be useful for advanced scenarios, for example to decode the * response differently depending on the response status: *

		 * Person person = client.get()
		 *     .uri("/people/1")
		 *     .accept(MediaType.APPLICATION_JSON)
		 *     .exchange((request, response) -> {
		 *         if (response.getStatusCode().equals(HttpStatus.OK)) {
		 *             return deserialize(response.getBody());
		 *         }
		 *         else {
		 *             throw new BusinessException();
		 *         }
		 *     });
		 * 
*

Note: The response is * {@linkplain ClientHttpResponse#close() closed} after the exchange * function has been invoked. * @param exchangeFunction the function to handle the response with * @param the type the response will be transformed to * @return the value returned from the exchange function */ default T exchange(ExchangeFunction exchangeFunction) { return exchange(exchangeFunction, true); } /** * Exchange the {@link ClientHttpResponse} for a type {@code T}. This * can be useful for advanced scenarios, for example to decode the * response differently depending on the response status: *

		 * Person person = client.get()
		 *     .uri("/people/1")
		 *     .accept(MediaType.APPLICATION_JSON)
		 *     .exchange((request, response) -> {
		 *         if (response.getStatusCode().equals(HttpStatus.OK)) {
		 *             return deserialize(response.getBody());
		 *         }
		 *         else {
		 *             throw new BusinessException();
		 *         }
		 *     });
		 * 
*

Note: If {@code close} is {@code true}, * then the response is {@linkplain ClientHttpResponse#close() closed} * after the exchange function has been invoked. When set to * {@code false}, the caller is responsible for closing the response. * @param exchangeFunction the function to handle the response with * @param close {@code true} to close the response after * {@code exchangeFunction} is invoked, {@code false} to keep it open * @param the type the response will be transformed to * @return the value returned from the exchange function */ T exchange(ExchangeFunction exchangeFunction, boolean close); /** * Defines the contract for {@link #exchange(ExchangeFunction)}. * @param the type the response will be transformed to */ @FunctionalInterface interface ExchangeFunction { /** * Exchange the given response into a type {@code T}. * @param clientRequest the request * @param clientResponse the response * @return the exchanged type * @throws IOException in case of I/O errors */ T exchange(HttpRequest clientRequest, ConvertibleClientHttpResponse clientResponse) throws IOException; } /** * Extension of {@link ClientHttpResponse} that can convert the body. */ interface ConvertibleClientHttpResponse extends ClientHttpResponse { /** * Extract the response body as an object of the given type. * @param bodyType the type of return value * @param the body type * @return the body, or {@code null} if no response body was available */ @Nullable T bodyTo(Class bodyType); /** * Extract the response body as an object of the given type. * @param bodyType the type of return value * @param the body type * @return the body, or {@code null} if no response body was available */ @Nullable T bodyTo(ParameterizedTypeReference bodyType); } } /** * Contract for specifying request headers and body leading up to the exchange. */ interface RequestBodySpec extends RequestHeadersSpec { /** * Set the length of the body in bytes, as specified by the * {@code Content-Length} header. * @param contentLength the content length * @return this builder * @see HttpHeaders#setContentLength(long) */ RequestBodySpec contentLength(long contentLength); /** * Set the {@linkplain MediaType media type} of the body, as specified * by the {@code Content-Type} header. * @param contentType the content type * @return this builder * @see HttpHeaders#setContentType(MediaType) */ RequestBodySpec contentType(MediaType contentType); /** * Set the body of the request to the given {@code Object}. * For example: *

		 * Person person = ... ;
		 * ResponseEntity<Void> response = client.post()
		 *     .uri("/persons/{id}", id)
		 *     .contentType(MediaType.APPLICATION_JSON)
		 *     .body(person)
		 *     .retrieve()
		 *     .toBodilessEntity();
		 * 
* @param body the body of the request * @return this builder */ RequestBodySpec body(Object body); /** * Set the body of the request to the given {@code Object}. * The parameter {@code bodyType} is used to capture the generic type. * @param body the body of the request * @param bodyType the type of the body, used to capture the generic type * @return this builder */ RequestBodySpec body(T body, ParameterizedTypeReference bodyType); /** * Set the body of the request to the given function that writes to * an {@link OutputStream}. * @param body a function that takes an {@code OutputStream} and can * throw an {@code IOException} * @return this builder */ RequestBodySpec body(StreamingHttpOutputMessage.Body body); } /** * Contract for specifying response operations following the exchange. */ interface ResponseSpec { /** * Provide a function to map specific error status codes to an error handler. *

By default, if there are no matching status handlers, responses with * status codes >= 400 wil throw a {@link RestClientResponseException}. *

Note that {@link IOException IOExceptions}, * {@link java.io.UncheckedIOException UncheckedIOExceptions}, and * {@link org.springframework.http.converter.HttpMessageNotReadableException HttpMessageNotReadableExceptions} * thrown from {@code errorHandler} will be wrapped in a * {@link RestClientException}. * @param statusPredicate to match responses with * @param errorHandler handler that typically, though not necessarily, * throws an exception * @return this builder */ ResponseSpec onStatus(Predicate statusPredicate, ErrorHandler errorHandler); /** * Provide a function to map specific error status codes to an error handler. *

By default, if there are no matching status handlers, responses with * status codes >= 400 wil throw a {@link RestClientResponseException}. *

Note that {@link IOException IOExceptions}, * {@link java.io.UncheckedIOException UncheckedIOExceptions}, and * {@link org.springframework.http.converter.HttpMessageNotReadableException HttpMessageNotReadableExceptions} * thrown from {@code errorHandler} will be wrapped in a * {@link RestClientException}. * @param errorHandler the error handler * @return this builder */ ResponseSpec onStatus(ResponseErrorHandler errorHandler); /** * Extract the body as an object of the given type. * @param bodyType the type of return value * @param the body type * @return the body, or {@code null} if no response body was available * @throws RestClientResponseException by default when receiving a * response with a status code of 4xx or 5xx. Use * {@link #onStatus(Predicate, ErrorHandler)} to customize error response * handling. */ @Nullable T body(Class bodyType); /** * Extract the body as an object of the given type. * @param bodyType the type of return value * @param the body type * @return the body, or {@code null} if no response body was available * @throws RestClientResponseException by default when receiving a * response with a status code of 4xx or 5xx. Use * {@link #onStatus(Predicate, ErrorHandler)} to customize error response * handling. */ @Nullable T body(ParameterizedTypeReference bodyType); /** * Return a {@code ResponseEntity} with the body decoded to an Object of * the given type. * @param bodyType the expected response body type * @param response body type * @return the {@code ResponseEntity} with the decoded body * @throws RestClientResponseException by default when receiving a * response with a status code of 4xx or 5xx. Use * {@link #onStatus(Predicate, ErrorHandler)} to customize error response * handling. */ ResponseEntity toEntity(Class bodyType); /** * Return a {@code ResponseEntity} with the body decoded to an Object of * the given type. * @param bodyType the expected response body type * @param response body type * @return the {@code ResponseEntity} with the decoded body * @throws RestClientResponseException by default when receiving a * response with a status code of 4xx or 5xx. Use * {@link #onStatus(Predicate, ErrorHandler)} to customize error response * handling. */ ResponseEntity toEntity(ParameterizedTypeReference bodyType); /** * Return a {@code ResponseEntity} without a body. * @return the {@code ResponseEntity} * @throws RestClientResponseException by default when receiving a * response with a status code of 4xx or 5xx. Use * {@link #onStatus(Predicate, ErrorHandler)} to customize error response * handling. */ ResponseEntity toBodilessEntity(); /** * Used in {@link #onStatus(Predicate, ErrorHandler)}. */ @FunctionalInterface interface ErrorHandler { /** * Handle the error in the given response. * @param response the response with the error * @throws IOException in case of I/O errors */ void handle(HttpRequest request, ClientHttpResponse response) throws IOException; } } /** * Contract for specifying request headers and URI for a request. * @param a self reference to the spec type */ interface RequestHeadersUriSpec> extends UriSpec, RequestHeadersSpec { } /** * Contract for specifying request headers, body and URI for a request. */ interface RequestBodyUriSpec extends RequestBodySpec, RequestHeadersUriSpec { } }