SpringBoot系列 - 使用RestTemplate

简介

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框架。

本篇介绍如何使用RestTemplate，以及在SpringBoot

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 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

// 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

// 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

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 {

    private static final Logger log = LoggerFactory.getLogger(RestClientConfig.class);

    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.setRequestFactory(clientHttpRequestFactory());
        restTemplate.setErrorHandler(new DefaultResponseErrorHandler());

        // 使用UTF-8编码集的conver替换默认的conver(默认的stringConver的编码集为"ISO-8859-1")，解决响应体乱码问题
        List> messageConverters = restTemplate.getMessageConverters();
        Iterator> iterator = messageConverters.iterator();
        while (iterator.hasNext()) {
            HttpMessageConverter converter = iterator.next();
            if (converter instanceof StringHttpMessageConverter) {
                iterator.remove();
            }
        }
        messageConverters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));

        //解决微信返回text/plain的解析
        //messageConverters.add(new WxMappingJackson2HttpMessageConverter());

        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

            //使用Httpclient连接池的方式配置(推荐)，同时支持netty，okHttp以及其他http框架
            PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);
            poolingHttpClientConnectionManager.setMaxTotal(100); // 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

            //设置默认请求头
            //List
 headers = new ArrayList<>();
            //headers.add(new BasicHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.16 Safari/537.36"));
            //headers.add(new BasicHeader("Accept-Encoding", "gzip,deflate"));
            //headers.add(new BasicHeader("Accept-Language", "zh-CN"));
            //headers.add(new BasicHeader("Connection", "Keep-Alive"));
            //httpClientBuilder.setDefaultHeaders(headers);

            HttpClient httpClient = httpClientBuilder.build();

            HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient); // httpClient连接配置
            clientHttpRequestFactory.setConnectTimeout(20000);              // 连接超时
            clientHttpRequestFactory.setReadTimeout(10000);                 // 数据读取超时时间，即SocketTimeout
            clientHttpRequestFactory.setConnectionRequestTimeout(200);      // 连接不够用的等待时间，不宜过长，必须设置，比如连接不够用时，时间过长将是灾难性的
            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，需要在项目构造工具配置文件中添加：

• pom.xml

    org.apache.httpcomponents
    httpclient
    4.5.3

• build.gradle

compile group: 'org.apache.httpcomponents', name: 'httpclient', version: '4.5.3'

发送文件

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

// 小文件
RequestEntity requestEntity = RequestEntity.get(uri).build();
ResponseEntity 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

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

    @Autowired
    private RestTemplate restTemplate;
}

实际使用例子

@RunWith(SpringRunner.class)
@SpringBootTest(classes = Application.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class ApplicationTests {

    private static final Logger logger = LoggerFactory.getLogger(ApplicationTests.class);
    
    /** @LocalServerPort 提供了 @Value("${local.server.port}") 的代替*/
    @LocalServerPort
    private int port;
    @Autowired
    private RestTemplate restTemplate;

    @Test
    public void testRestTemplate() {
        logger.info("解绑成功后推送消息给对应的POS机");
        LoginParam param = new LoginParam();
        param.setUsername("admin");
        param.setPassword("12345678");
        String loginUrl = String.format("http://localhost:%d/login", port);
        BaseResponse r = restTemplate.postForObject(loginUrl, param, BaseResponse.class);
        assertThat(r.isSuccess(), is(true));

        logger.info("推送消息登录认证成功");
        String token = (String) r.getData();
        UnbindParam unbindParam = new UnbindParam();
        unbindParam.setImei("imei");
        unbindParam.setLocation("location");
        // 设置HTTP Header信息
        String unbindUrl = String.format("http://localhost:%d/unbind", port);
        URI uri;
        try {
            uri = new URI(unbindUrl);
        } catch (URISyntaxException e) {
            logger.error("URI构建失败", e);
            throw new RuntimeException("URI构建失败");
        }
        RequestEntity requestEntity = RequestEntity
                .post(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .accept(MediaType.APPLICATION_JSON)
                .header("Authorization", token)
                .body(unbindParam);
        ResponseEntity responseEntity = restTemplate.exchange(requestEntity, BaseResponse.class);
        BaseResponse r2 = responseEntity.getBody();
        assertThat(r2.isSuccess(), is(true));
        assertThat(r2.getData(), is("unbind"));
    }

}