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