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：
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 {
@Override
public void handleError(ClientHttpResponse response) throws IOException {
// todo
}
}然后设置下异常处理器：
@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：
@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<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>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：
<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>>() {
@Override
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
@Service
public class DeviceService {
private static final Logger logger = LoggerFactory.getLogger(DeviceService.class); @Resource
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");
}