SpringBoot 3.2引入了新的 RestClient 用于http接口调用，采用了 fluent API 的风格，可以进行链式调用。

具体的代码参照 示例项目 https://github.com/qihaiyan/springcamp/tree/master/spring-jdbc-client

一、概述

RestClient 是一个类似于 RestTemplate 的的同步接口调用工具。相比于 RestTemplate 采用的是 template 设计模式，RestClient 采用了 fluent API 风格，简单灵活，易于阅读和维护。

二、引入 RestClient

首先引入 spring-boot-starter-web 依赖。

在 build.gradle 中增加一行代码:

implementation 'org.springframework.boot:spring-boot-starter-web'

对 RestClient 进行配置：

@Configuration
public class RestClientConfig {public CloseableHttpClient httpClient() {Registry<ConnectionSocketFactory> registry =RegistryBuilder.<ConnectionSocketFactory>create().register("http", PlainConnectionSocketFactory.getSocketFactory()).register("https", SSLConnectionSocketFactory.getSocketFactory()).build();PoolingHttpClientConnectionManager poolingConnectionManager = new PoolingHttpClientConnectionManager(registry);poolingConnectionManager.setDefaultSocketConfig(SocketConfig.custom().setSoTimeout(Timeout.ofSeconds(2)).build());poolingConnectionManager.setDefaultConnectionConfig(ConnectionConfig.custom().setConnectTimeout(Timeout.ofSeconds(2)).build());// set total amount of connections across all HTTP routespoolingConnectionManager.setMaxTotal(200);// set maximum amount of connections for each http route in poolpoolingConnectionManager.setDefaultMaxPerRoute(200);RequestConfig requestConfig = RequestConfig.custom().setConnectionKeepAlive(TimeValue.ofSeconds(10)).setConnectionRequestTimeout(Timeout.ofSeconds(2)).setResponseTimeout(Timeout.ofSeconds(2)).build();return HttpClients.custom().setDefaultRequestConfig(requestConfig).setConnectionManager(poolingConnectionManager).setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy()).build();}@Slf4jstatic class CustomClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {@Override@NonNullpublic ClientHttpResponse intercept(HttpRequest request, @NonNull byte[] bytes, @NonNull ClientHttpRequestExecution execution) throws IOException {log.info("HTTP Method: {}, URI: {}, Headers: {}", request.getMethod(), request.getURI(), request.getHeaders());request.getMethod();if (request.getMethod().equals(HttpMethod.POST)) {log.info("HTTP body: {}", new String(bytes, StandardCharsets.UTF_8));}ClientHttpResponse response = execution.execute(request, bytes);ClientHttpResponse responseWrapper = new BufferingClientHttpResponseWrapper(response);String body = StreamUtils.copyToString(responseWrapper.getBody(), StandardCharsets.UTF_8);log.info("RESPONSE body: {}", body);return responseWrapper;}}static class BufferingClientHttpResponseWrapper implements ClientHttpResponse {private final ClientHttpResponse response;private byte[] body;BufferingClientHttpResponseWrapper(ClientHttpResponse response) {this.response = response;}@NonNullpublic HttpStatusCode getStatusCode() throws IOException {return this.response.getStatusCode();}@NonNullpublic String getStatusText() throws IOException {return this.response.getStatusText();}@NonNullpublic HttpHeaders getHeaders() {return this.response.getHeaders();}@NonNullpublic InputStream getBody() throws IOException {if (this.body == null) {this.body = StreamUtils.copyToByteArray(this.response.getBody());}return new ByteArrayInputStream(this.body);}public void close() {this.response.close();}}@Beanpublic RestTemplate restTemplate(RestTemplateBuilder builder) {return builder.requestFactory(() -> new HttpComponentsClientHttpRequestFactory(httpClient())).interceptors(new CustomClientHttpRequestInterceptor()).build();}@Beanpublic RestClient restClient(RestTemplate restTemplate) {return RestClient.builder(restTemplate).requestFactory(new HttpComponentsClientHttpRequestFactory(httpClient())).build();}
}

在配置中我们仍然定义了 RestTemplate ，并使用 RestTemplate 来初始化 RestClient 为的是继续使用 RestTemplate 的日志打印功能 参照 https://github.com/qihaiyan/springcamp/tree/master/spring-rest-template-log

如果不想继续使用RestTemplate，那初始化代码可以改为

RestClient.builder().requestFactory(new HttpComponentsClientHttpRequestFactory(httpClient())).build();

同时我们给 RestClient 配置了 requestFactory ，可以使用长连接调用接口。

三、GET接口调用

调用GET接口返回字符串：

restClient.get().uri("https://httpbin.org/get").retrieve().body(String.class)

调用GET接口对象：

restClient.get().uri("https://httpbin.org/get").retrieve().body(MyData.class);

调用GET接口返回List：

List<String> list = restClient.get().uri("http://someservice/list").retrieve().body(new ParameterizedTypeReference<>() {});

四、POST接口调用

MyData postBody = new MyData("test", "test RestClient");ResponseEntity<String> respObj = restClient.post().uri("https://httpbin.org/post").contentType(MediaType.APPLICATION_JSON).body(postBody).retrieve().toEntity(String.class);

五、Exchange接口调用

当需要对接口返回结果进行更加精确的控制时，可以采用 Exchange 方法。
例如当接口返回 4xx 时，让 restClient 返回空字符串，否则返回正常结果：

restClient.get().uri("https://httpbin.org/get").accept(MediaType.APPLICATION_JSON).exchange((request, response) -> {if (response.getStatusCode().is4xxClientError()) {log.info("status 4xx");return "";} else {log.info("response: {}", response);return response;}});

六、错误处理

当接口返回错误时，可以在 onStatus 方法中进行判断并进行对应的操作：

restClient.get().uri("https://httpbin.org/status/404").retrieve().onStatus(status -> status.value() == 404, (request, response) -> {log.info("status 404");}).toBodilessEntity();

toBodilessEntity 方法是一种忽略接口返回结果的方法，当不需要读取接口返回结果时，可以使用 toBodilessEntity 方法。