一，序

现如今的 IT 项目，由服务端向外发起网络请求的场景，基本上处处可见！
传统情况下，在服务端代码里访问 http 服务时，一般会使用 JDK 的 HttpURLConnection 或者 Apache 的 HttpClient，不过这种方法使用起来太过繁琐，而且 api 使用起来非常的复杂，还得操心资源回收。

其实Spring已经为我们提供了一种简单便捷的模板类来进行操作，它就是RestTemplate

RestTemplate是一个执行HTTP请求的同步阻塞式工具类，它仅仅只是在 HTTP 客户端库（例如 JDK HttpURLConnection，Apache HttpComponents，okHttp 等）基础上，封装了更加简单易用的模板方法 API，方便程序员利用已提供的模板方法发起网络请求和处理，能很大程度上提升我们的开发效率

二，模板注册

Spring RestTemplate 调用REST API 给我们的开发工作带来了极大的方便， 默认的SimpleClientHttpRequestFactory 并不支持https的调用，我们可以通过引入Apache HttpClient实现对https的调用支持。

RestTemplateConfig.java

import java.nio.charset.StandardCharsets;import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.web.client.RestTemplate;/*** * 注册 RestTemplate* * @author 00fly* @version [版本号, 2018年11月20日]* @see [相关类/方法]* @since [产品/模块版本]*/
@Configuration
public class RestTemplateConfig
{@Beanpublic RestTemplate restTemplate(){ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient());RestTemplate restTemplate = new RestTemplate(requestFactory);// RestTemplate设置编码restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8));return restTemplate;}/*** Apache HttpClient* * @return* @see [类、类#方法、类#成员]*/private HttpClient httpClient(){// 支持HTTP、HTTPSRegistry<ConnectionSocketFactory> registry =RegistryBuilder.<ConnectionSocketFactory> create().register("http", PlainConnectionSocketFactory.getSocketFactory()).register("https", SSLConnectionSocketFactory.getSocketFactory()).build();PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(registry);connectionManager.setMaxTotal(200);connectionManager.setDefaultMaxPerRoute(100);connectionManager.setValidateAfterInactivity(2000);RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(65000) // 服务器返回数据(response)的时间，超时抛出read timeout.setConnectTimeout(5000) // 连接上服务器(握手成功)的时间，超时抛出connect timeout.setConnectionRequestTimeout(1000)// 从连接池中获取连接的超时时间，超时抛出ConnectionPoolTimeoutException.build();return HttpClientBuilder.create().setDefaultRequestConfig(requestConfig).setConnectionManager(connectionManager).build();}
}

三，调用打开方式

1，组件引入

除了springboot框架外，主要引入如下组件：

pom.xml

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.47</version></dependency><dependency><groupId>commons-io</groupId><artifactId>commons-io</artifactId><version>2.5</version></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-lang3</artifactId></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><scope>provided</scope></dependency>

2，调用方式

1）get

    @Testpublic void testGET1(){String url = "https://www.baidu.com/";ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);log.info("ResponseEntity StatusCode={}", responseEntity.getStatusCode());log.info("ResponseEntity={}", responseEntity);}@Testpublic void testGET2(){String url = "https://www.so.com/";String responseBody = restTemplate.getForObject(url, String.class);log.info("responseBody={}", responseBody);}

2）post

  @Testpublic void testPOST(){// POST请求只能用MultiValueMapString url = "http://httpbin.org/post";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));MultiValueMap<String, String> params = new LinkedMultiValueMap<>();params.add("id", "123456");HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);}

3）WebService

    @Testpublic void testWebService()throws IOException{String url = "http://127.0.0.1:7879/demo/services/ws_inputService";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.TEXT_XML);headers.setAccept(Arrays.asList(MediaType.TEXT_XML));InputStream is = this.getClass().getResourceAsStream("/request");String requestString = IOUtils.toString(is, "utf-8");HttpEntity<String> requestEntity = new HttpEntity<>(requestString, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity Body = {}", responseEntity.getBody());}

4）JsonRequestBody

  /*** 演示@RequestBody请求*/@Testpublic void testJsonRequestBody(){String url = "https://www.so.com/s";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));// 方式1SearchReq req = new SearchReq();req.setPageNo(1);req.setPageSize(5);HttpEntity<SearchReq> requestEntity = new HttpEntity<>(req, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);// 方式2Map<String, String> map = new HashMap<>();map.put("pageNo", "1");map.put("pageSize", "10");HttpEntity<Map<String, String>> requestEntity2 = new HttpEntity<>(map, headers);ResponseEntity<String> responseEntity2 = restTemplate.postForEntity(url, requestEntity2, String.class);log.info("ResponseEntity={}", responseEntity2);// 方式3map.clear();map.put("pageNo", "1");map.put("pageSize", "2");HttpEntity<String> requestEntity3 = new HttpEntity<>(JSONObject.toJSONString(map), headers);ResponseEntity<String> responseEntity3 = restTemplate.postForEntity(url, requestEntity3, String.class);log.info("ResponseEntity={}", responseEntity3);}

5）get、post 统一调用 restTemplate.exchange

 @Testpublic void testExchange(){String url = "https://www.so.com/s";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));headers.add("token", "Bearer");MultiValueMap<String, Object> params = new LinkedMultiValueMap<>();params.add("type", 1);HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity;// GET with headersresponseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);// POSTresponseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);}

6）文件上传 MultipartFile、MultipartFile[ ]

    @Testpublic void testPOST(){// POST请求只能用MultiValueMapString url = "http://127.0.0.1:8080/post";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.MULTIPART_FORM_DATA);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));// 注意：FileSystemResource只适用于文件，Jar內运行报错MultiValueMap<String, Object> params = new LinkedMultiValueMap<>();String path = new ClassPathResource("123.jpg").getPath();FileSystemResource file = new FileSystemResource(path);// 多次调用，后台接受到的是MultipartFile[]params.add("file", file);params.add("file", file);params.add("file", file);params.add("name", "girl");params.add("age", "18");HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);}@Testpublic void testPOST2(){// POST请求只能用MultiValueMapString url = "http://127.0.0.1:8080/post";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.MULTIPART_FORM_DATA);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));// Resource适用于文件、Jar內MultiValueMap<String, Object> params = new LinkedMultiValueMap<>();Resource file = new ClassPathResource("123.jpg");// 多次调用，后台接受到的是MultipartFile[]params.add("file", file);params.add("file", file);params.add("file", file);params.add("name", "girl");params.add("age", "18");HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);}

7) url支持占位符

@Testpublic void testGET(){/**** url支持占位符 ****/String url = "http://localhost:8080/rest/user/list/{page}";String response = restTemplate.getForObject(url, String.class, 1);log.info("ResponseBody={}", response);ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class, 1);log.info("ResponseEntity={}", responseEntity);}@Testpublic void testPOST(){/**** url支持占位符 ****/String url = "http://localhost:8080/rest/user/list/{page}";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);MultiValueMap<String, String> params = new LinkedMultiValueMap<>();params.add("username", "user001");params.add("password", "123456");HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity;String response = restTemplate.postForObject(url, requestEntity, String.class, 1);log.info("ResponseBody={}", response);responseEntity = restTemplate.postForEntity(url, requestEntity, String.class, 1);log.info("ResponseEntity={}", responseEntity);}/*** 演示@RequestBody请求*/@Testpublic void testJsonRequestBody(){String url = "http://127.0.0.1/api/common/search";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));// 方式1SearchReq req = new SearchReq();req.setPageNo(1);req.setPageSize(2);HttpEntity<SearchReq> requestEntity = new HttpEntity<>(req, headers);ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);// 方式2Map<String, String> map = new HashMap<>();map.put("pageNo", "1");map.put("pageSize", "10");HttpEntity<Map<String, String>> requestEntity2 = new HttpEntity<>(map, headers);ResponseEntity<String> responseEntity2 = restTemplate.postForEntity(url, requestEntity2, String.class);log.info("ResponseEntity={}", responseEntity2);// 方式3map.clear();map.put("pageNo", "1");map.put("pageSize", "2");HttpEntity<String> requestEntity3 = new HttpEntity<>(JSON.toJSONString(map), headers);ResponseEntity<String> responseEntity3 = restTemplate.postForEntity(url, requestEntity3, String.class);log.info("ResponseEntity={}", responseEntity3);}@Testpublic void testExchange(){/**** url支持占位符 ****/String url = "http://localhost:8080/rest/user/list/{page}";HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));MultiValueMap<String, String> params = new LinkedMultiValueMap<>();params.add("username", "用户1");params.add("password", "123456");HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity<>(params, headers);ResponseEntity<String> responseEntity;// GET、POSTresponseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class, 1);log.info("ResponseEntity={}", responseEntity);Map<String, Integer> vars = Collections.singletonMap("page", 1);responseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class, vars);log.info("ResponseEntity={}", responseEntity);}@Data
class SearchReq
{Integer pageNo = 1;Integer pageSize = 10;String keyword;
}

8) 后台下载文件保存

        String downUrl =  "http://127.0.0.1:8080/file/down";ResponseEntity<byte[]> responseEntity = restTemplate.getForEntity(downUrl, byte[].class);byte[] body = responseEntity.getBody();// 数据落地File rootDir = new File("upload");rootDir.mkdirs();File dest = new File(rootDir.getCanonicalPath() + File.separator + RandomStringUtils.randomNumeric(5) + resource.getFilename());try (FileOutputStream fos = new FileOutputStream(dest)){fos.write(body);}

9）文件流后台转发

String downUrl =  "http://127.0.0.1:8080/file/down";byte[] bytes = restTemplate.getForEntity(downUrl, byte[].class).getBody();// 字节流转发到上传接口HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.MULTIPART_FORM_DATA);headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));MultiValueMap<String, Object> params = new LinkedMultiValueMap<>();Resource byteResource = new ByteArrayResource(bytes){@Overridepublic String getFilename(){return resource.getFilename();}@Overridepublic long contentLength(){return bytes.length;}};params.add("file", byteResource);params.add("id", "1");HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(params, headers);String uploadUrl = "http://127.0.0.1:8080/file/upload";ResponseEntity<String> responseEntity = restTemplate.postForEntity(uploadUrl, requestEntity, String.class);log.info("ResponseEntity={}", responseEntity);

有任何问题和建议，都可以向我提问讨论,大家一起进步，谢谢!

–over–