SpringBoot系列 - 使用RestTemplate

spring框架提供的RestTemplate类可用于在应用中调用rest服务，它简化了与http服务的通信方式，统一了RESTful的标准，封装了http链接， 我们只需要传入url及返回值类型即可。相较于之前常用的HttpClient，RestTemplate是一种更优雅的调用RESTful服务的方式。
RestTemplate默认依赖JDK提供http连接的能力（HttpURLConnection），如果有需要的话也可以通过setRequestFactory方法替换为例如 Apache HttpComponents、Netty或OkHttp等其它HTTP library。
本篇介绍如何使用RestTemplate，以及在SpringBoot里面的配置和注入。

实现逻辑
RestTemplate包含以下几个部分：

HttpMessageConverter 对象转换器

ClientHttpRequestFactory 默认是JDK的HttpURLConnection

ResponseErrorHandler 异常处理

ClientHttpRequestInterceptor 请求拦截器
用一张图可以很直观的理解：

直接使用方式很简单：

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public class RestTemplateTest { public static void main(String[] args) { RestTemplate restT = new RestTemplate(); //通过Jackson JSON processing library直接将返回值绑定到对象 Quote quote = restT.getForObject("http://gturnquist-quoters.cfapps.io/api/random", Quote.class); String quoteString = restT.getForObject("http://gturnquist-quoters.cfapps.io/api/random", String.class); System.out.println(quoteString); } }

发送GET请求

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// 1-getForObject() User user1 = this.restTemplate.getForObject(uri, User.class); // 2-getForEntity() ResponseEntity responseEntity1 = this.restTemplate.getForEntity(uri, User.class); HttpStatus statusCode = responseEntity1.getStatusCode(); HttpHeaders header = responseEntity1.getHeaders(); User user2 = responseEntity1.getBody(); // 3-exchange() RequestEntity requestEntity = RequestEntity.get(new URI(uri)).build(); ResponseEntity responseEntity2 = this.restTemplate.exchange(requestEntity, User.class); User user3 = responseEntity2.getBody();

发送POST请求

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// 1-postForObject() User user1 = this.restTemplate.postForObject(uri, user, User.class); // 2-postForEntity() ResponseEntity responseEntity1 = this.restTemplate.postForEntity(uri, user, User.class); // 3-exchange() RequestEntity requestEntity = RequestEntity.post(new URI(uri)).body(user); ResponseEntity responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);

设置HTTP Header

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// 1-Content-Type RequestEntity requestEntity = RequestEntity .post(new URI(uri)) .contentType(MediaType.APPLICATION_JSON) .body(user); // 2-Accept RequestEntity requestEntity = RequestEntity .post(new URI(uri)) .accept(MediaType.APPLICATION_JSON) .body(user); // 3-Other RequestEntity requestEntity = RequestEntity .post(new URI(uri)) .header("Authorization", "Basic " + base64Credentials) .body(user);

捕获异常
捕获 HttpServerErrorException

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try { responseEntity = restTemplate.exchange(requestEntity, String.class); } catch (HttpServerErrorException e) { // log error }

自定义异常处理器

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public class CustomErrorHandler extends DefaultResponseErrorHandler { @Override public void handleError(ClientHttpResponse response) throws IOException { // todo } }

然后设置下异常处理器：

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@Configuration public class RestClientConfig { @Bean public RestTemplate restTemplate() { RestTemplate restTemplate = new RestTemplate(); restTemplate.setErrorHandler(new CustomErrorHandler()); return restTemplate; } }

配置类
创建 RestClientConfig 类，设置连接池大小、超时时间、重试机制等。配置如下：

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@Configuration public class RestClientConfig { @Bean public RestTemplate restTemplate() { RestTemplate restTemplate = new RestTemplate(); restTemplate.setRequestFactory(clientHttpRequestFactory()); restTemplate.setErrorHandler(new DefaultResponseErrorHandler()); return restTemplate; } @Bean public HttpComponentsClientHttpRequestFactory clientHttpRequestFactory() { try { HttpClientBuilder httpClientBuilder = HttpClientBuilder.create(); SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(null, new TrustStrategy() { public boolean isTrusted(X509Certificate[] arg0, String arg1) throws CertificateException { return true; } }).build(); httpClientBuilder.setSSLContext(sslContext); HostnameVerifier hostnameVerifier = NoopHostnameVerifier.INSTANCE; SSLConnectionSocketFactory sslConnectionSocketFactory = new SSLConnectionSocketFactory(sslContext, hostnameVerifier); Registry socketFactoryRegistry = RegistryBuilder.create() .register("http", PlainConnectionSocketFactory.getSocketFactory()) .register("https", sslConnectionSocketFactory).build();// 注册http和https请求 // 开始设置连接池 PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry); poolingHttpClientConnectionManager.setMaxTotal(500); // 最大连接数500 poolingHttpClientConnectionManager.setDefaultMaxPerRoute(100); // 同路由并发数100 httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager); httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(3, true)); // 重试次数 HttpClient httpClient = httpClientBuilder.build(); HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient); // httpClient连接配置 clientHttpRequestFactory.setConnectTimeout(20000); // 连接超时 clientHttpRequestFactory.setReadTimeout(30000); // 数据读取超时时间 clientHttpRequestFactory.setConnectionRequestTimeout(20000); // 连接不够用的等待时间 return clientHttpRequestFactory; } catch (KeyManagementException | NoSuchAlgorithmException | KeyStoreException e) { log.error("初始化HTTP连接池出错", e); } return null; } }

注意，如果没有apache的HttpClient类，需要在pom文件中添加：

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<dependency> <groupId>org.apache.httpcomponentsgroupId> <artifactId>httpclientartifactId> <version>4.5.3version> dependency>

发送文件

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MultiValueMap multiPartBody = new LinkedMultiValueMap<>(); multiPartBody.add("file", new ClassPathResource("/tmp/user.txt")); RequestEntity> requestEntity = RequestEntity .post(uri) .contentType(MediaType.MULTIPART_FORM_DATA) .body(multiPartBody);

下载文件

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// 小文件 RequestEntity requestEntity = RequestEntity.get(uri).build(); ResponseEntity<byte[]> responseEntity = restTemplate.exchange(requestEntity, byte[].class); byte[] downloadContent = responseEntity.getBody(); // 大文件 ResponseExtractor> responseExtractor = new ResponseExtractor>() { @Override public ResponseEntity extractData(ClientHttpResponse response) throws IOException { File rcvFile = File.createTempFile("rcvFile", "zip"); FileCopyUtils.copy(response.getBody(), new FileOutputStream(rcvFile)); return ResponseEntity.status(response.getStatusCode()).headers(response.getHeaders()).body(rcvFile); } }; File getFile = this.restTemplate.execute(targetUri, HttpMethod.GET, null, responseExtractor);

Service注入

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@Service public class DeviceService { private static final Logger logger = LoggerFactory.getLogger(DeviceService.class); @Resource private RestTemplate restTemplate; }

实际使用例子

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// 开始推送消息 logger.info("解绑成功后推送消息给对应的POS机"); LoginParam loginParam = new LoginParam(); loginParam.setUsername(managerInfo.getUsername()); loginParam.setPassword(managerInfo.getPassword()); HttpBaseResponse r = restTemplate.postForObject( p.getPosapiUrlPrefix() + "/notifyLogin", loginParam, HttpBaseResponse.class); if (r.isSuccess()) { logger.info("推送消息登录认证成功"); String token = (String) r.getData(); UnbindParam unbindParam = new UnbindParam(); unbindParam.setImei(pos.getImei()); unbindParam.setLocation(location); // 设置HTTP Header信息 URI uri; try { uri = new URI(p.getPosapiUrlPrefix() + "/notify/unbind"); } catch (URISyntaxException e) { logger.error("URI构建失败", e); return 1; } RequestEntity requestEntity = RequestEntity .post(uri) .contentType(MediaType.APPLICATION_JSON) .accept(MediaType.APPLICATION_JSON) .header("Authorization", token) .body(unbindParam); ResponseEntity responseEntity = restTemplate.exchange(requestEntity, HttpBaseResponse.class); HttpBaseResponse r2 = responseEntity.getBody(); if (r2.isSuccess()) { logger.info("推送消息解绑网点成功"); } else { logger.error("推送消息解绑网点失败，errmsg = " + r2.getMsg()); } } else { logger.error("推送消息登录认证失败"); }

GitHub源码

springboot-resttemplate