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：

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

// 1-getForObject()
User user1 = this.restTemplate.getForObject(uri, User.class);// 2-getForEntity()
ResponseEntity<User> 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<User> responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);
User user3 = responseEntity2.getBody();

发送POST请求

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

设置HTTP Header

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

捕获异常
捕获HttpServerErrorException

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

自定义异常处理器

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

然后设置下异常处理器：

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

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

/*** - Supports both HTTP and HTTPS* - Uses a connection pool to re-use connections and save overhead of creating connections.* - Has a custom connection keep-alive strategy (to apply a default keep-alive if one isn't specified)* - Starts an idle connection monitor to continuously clean up stale connections.** @author XiongNeng* @version 1.0* @since 2018/7/5*/public class HttpClientConfig {private static final Logger LOGGER = LoggerFactory.getLogger(HttpClientConfig.class);private HttpClientProperties p;public PoolingHttpClientConnectionManager poolingConnectionManager() {SSLContextBuilder builder = new SSLContextBuilder();try {builder.loadTrustMaterial(null, new TrustStrategy() {public boolean isTrusted(X509Certificate[] arg0, String arg1) {return true;}});} catch (NoSuchAlgorithmException | KeyStoreException e) {LOGGER.error("Pooling Connection Manager Initialisation failure because of " + e.getMessage(), e);}SSLConnectionSocketFactory sslsf = null;try {sslsf = new SSLConnectionSocketFactory(builder.build());} catch (KeyManagementException | NoSuchAlgorithmException e) {LOGGER.error("Pooling Connection Manager Initialisation failure because of " + e.getMessage(), e);}Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create().register("https", sslsf).register("http", new PlainConnectionSocketFactory()).build();PoolingHttpClientConnectionManager poolingConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);poolingConnectionManager.setMaxTotal(p.getMaxTotalConnections());  //最大连接数poolingConnectionManager.setDefaultMaxPerRoute(p.getDefaultMaxPerRoute());  //同路由并发数return poolingConnectionManager;}public ConnectionKeepAliveStrategy connectionKeepAliveStrategy() {return new ConnectionKeepAliveStrategy() {public long getKeepAliveDuration(HttpResponse response, HttpContext httpContext) {HeaderElementIterator it = new BasicHeaderElementIterator(response.headerIterator(HTTP.CONN_KEEP_ALIVE));while (it.hasNext()) {HeaderElement he = it.nextElement();String param = he.getName();String value = he.getValue();if (value != null && param.equalsIgnoreCase("timeout")) {return Long.parseLong(value) * 1000;}}return p.getDefaultKeepAliveTimeMillis();}};}public CloseableHttpClient httpClient() {RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(p.getRequestTimeout()).setConnectTimeout(p.getConnectTimeout()).setSocketTimeout(p.getSocketTimeout()).build();return HttpClients.custom().setDefaultRequestConfig(requestConfig).setConnectionManager(poolingConnectionManager()).setKeepAliveStrategy(connectionKeepAliveStrategy()).setRetryHandler(new DefaultHttpRequestRetryHandler(3, true))  // 重试次数.build();}public Runnable idleConnectionMonitor(final PoolingHttpClientConnectionManager connectionManager) {return new Runnable() {(fixedDelay = 10000)public void run() {try {if (connectionManager != null) {LOGGER.trace("run IdleConnectionMonitor - Closing expired and idle connections...");connectionManager.closeExpiredConnections();connectionManager.closeIdleConnections(p.getCloseIdleConnectionWaitTimeSecs(), TimeUnit.SECONDS);} else {LOGGER.trace("run IdleConnectionMonitor - Http Client Connection manager is not initialised");}} catch (Exception e) {LOGGER.error("run IdleConnectionMonitor - Exception occurred. msg={}, e={}", e.getMessage(), e);}}};}public TaskScheduler taskScheduler() {ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();scheduler.setThreadNamePrefix("poolScheduler");scheduler.setPoolSize(50);return scheduler;}
}

然后再配置RestTemplateConfig类，使用之前配置好的CloseableHttpClient类注入，同时配置一些默认的消息转换器：

/*** RestTemplate客户端连接池配置** @author XiongNeng* @version 1.0* @since 2018/1/24*/(proxyTargetClass = true)
public class RestTemplateConfig {private CloseableHttpClient httpClient;public RestTemplate restTemplate(MappingJackson2HttpMessageConverter jackson2HttpMessageConverter) {RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory());List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter(Charset.forName("utf-8"));messageConverters.add(stringHttpMessageConverter);messageConverters.add(jackson2HttpMessageConverter);restTemplate.setMessageConverters(messageConverters);return restTemplate;}public HttpComponentsClientHttpRequestFactory clientHttpRequestFactory() {HttpComponentsClientHttpRequestFactory rf = new HttpComponentsClientHttpRequestFactory();rf.setHttpClient(httpClient);return rf;}}

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

<dependency><groupId>org.apache.httpcomponents</groupId><artifactId>httpclient</artifactId><version>4.5.3</version>
</dependency>

发送文件

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

下载文件

// 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<ResponseEntity<File>> responseExtractor = new ResponseExtractor<ResponseEntity<File>>() {public ResponseEntity<File> 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

public class DeviceService {private static final Logger logger = LoggerFactory.getLogger(DeviceService.class);private RestTemplate restTemplate;
}
实际使用例子
// 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<UnbindParam> requestEntity = RequestEntity.post(uri).contentType(MediaType.APPLICATION_JSON).accept(MediaType.APPLICATION_JSON).header("Authorization", token).body(unbindParam);ResponseEntity<HttpBaseResponse> 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

https://github.com/yidao620c/SpringBootBucket/tree/master/springboot-resttemplate

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