聊聊RestTemplate对HttpClient的适配

序

本文主要研究一下RestTemplate对HttpClient的适配

ClientHttpRequestFactory

org/springframework/http/client/ClientHttpRequestFactory.java

spring-web定义了ClientHttpRequestFactory接口，它定义了一个createRequest方法

HttpComponentsClientHttpRequestFactory

org/springframework/http/client/HttpComponentsClientHttpRequestFactory.java

HttpComponentsClientHttpRequestFactory实现了ClientHttpRequestFactory及DisposableBean接口；createRequest方法先拿到httpClient，然后创建createHttpUriRequest，设置RequestConfig，针对bufferRequestBody的场景HttpComponentsClientHttpRequest，否则创建HttpComponentsStreamingClientHttpRequest；destroy方法主要是关闭httpClient

ClientHttpRequest

org/springframework/http/client/ClientHttpRequest.java

ClientHttpRequest接口定义了execute方法，它返回ClientHttpResponse

HttpComponentsClientHttpRequest

org/springframework/http/client/HttpComponentsClientHttpRequest.java

HttpComponentsClientHttpRequest继承了AbstractBufferingClientHttpRequest，其executeInternal方法调用httpClient.execute，然后返回HttpComponentsClientHttpResponse

HttpComponentsStreamingClientHttpRequest

org/springframework/http/client/HttpComponentsStreamingClientHttpRequest.java

HttpComponentsStreamingClientHttpRequest继承了AbstractClientHttpRequest，实现了StreamingHttpOutputMessage接口，其getBodyInternal抛出UnsupportedOperationException，其executeInternal方法创建的是StreamingHttpEntity，然后执行httpClient.execute(this.httpRequest, this.httpContext)，最后返回HttpComponentsClientHttpResponse

ClientHttpResponse

org/springframework/http/client/ClientHttpResponse.java

ClientHttpResponse接口定义了getStatusCode、getRawStatusCode、getStatusText、close方法

HttpComponentsClientHttpResponse

org/springframework/http/client/HttpComponentsClientHttpResponse.java

HttpComponentsClientHttpResponse继承了AbstractClientHttpResponse，其getBody方法返回的是httpResponse.getEntity().getContent()或者StreamUtils.emptyInput()，其close方法主要是执行EntityUtils.consume(this.httpResponse.getEntity())以及((Closeable) this.httpResponse).close()

小结

spring-web定义了ClientHttpRequestFactory接口，它定义了一个createRequest方法，HttpComponentsClientHttpRequestFactory就是RestTemplate对HttpClient的适配，其通过HttpComponentsClientHttpRequest或者HttpComponentsStreamingClientHttpRequest，将HttpClient的request适配为了spring-web的ClientHttpRequest，将response通过HttpComponentsClientHttpResponse适配为spring-web的ClientHttpResponse。