RestTemplate 学习笔记

简介

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

依赖

1、非Spring环境下使用RestTemplate

<dependency><groupId>org.springframework</groupId><artifactId>spring-web</artifactId>
</dependency>

2、Spring环境下使用 RestTemplate

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId>
</dependency>

初始化配置

@Configuration
public class RestTemplateConfig {@Beanpublic RestTemplate restTemplate(){RestTemplate restTemplate = new RestTemplate(simpleClientHttpRequestFactory());return restTemplate;}public ClientHttpRequestFactory simpleClientHttpRequestFactory() {SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();factory.setReadTimeout(150000); // msfactory.setConnectTimeout(150000); // msreturn factory;}}

这种初始化方法，是使用了JDK自带的HttpURLConnection作为底层HTTP客户端实现。

可以执行配置不同的连接方式，如

HttpClient

@Configuration
public class RestTemplateConfig {@Beanpublic RestTemplate restTemplate(){RestTemplate restTemplate = new RestTemplate(getClientHttpRequestFactory());return restTemplate;}/*** 使用HttpClient作为底层客户端* @return*/private ClientHttpRequestFactory getClientHttpRequestFactory() {int timeout = 5000;RequestConfig config = RequestConfig.custom().setConnectTimeout(timeout).setConnectionRequestTimeout(timeout).setSocketTimeout(timeout).build();CloseableHttpClient client = HttpClientBuilder.create().setDefaultRequestConfig(config).build();return new HttpComponentsClientHttpRequestFactory(client);}
}

OkHttp

/*** 使用OkHttpClient作为底层客户端* @return*/
private ClientHttpRequestFactory getClientHttpRequestFactory(){OkHttpClient okHttpClient = new OkHttpClient.Builder().connectTimeout(5, TimeUnit.SECONDS).writeTimeout(5, TimeUnit.SECONDS).readTimeout(5, TimeUnit.SECONDS).build();return new OkHttp3ClientHttpRequestFactory(okHttpClient);
}

使用

restTemplate 提供的api

1、设置Header和 body

// 创建 HttpEntity
String jsonBody = JSONObject.toJSONString(weChatRefundsRequestDto);
HttpEntity<String> entity = new HttpEntity<>(jsonBody, headers);ResponseEntity<WechatRefundsResponseDto> responseEntity =restTemplate.postForEntity("url",entity,WechatRefundsResponseDto.class);

其中在entity 中设置请求头和请求体;WechatRefundsResponseDto为设置接受返回信息的对象，其他postObject 类似以上方式

public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request,Class<T> responseType, Object... uriVariables) throws RestClientException

其中postObeject，postForEntity的请求方式中的request如果类型为HttpEntity则直接使用，不是就将request当成body放入HttpEntity中使用

2、get请求设置带参数的请求

@Autowired
private RestTemplate restTemplate;/*** 单元测试（带参的get请求）*/
@Test
public void testGetByRestFul(){//请求地址String url = "http://localhost:8080/testGetByRestFul/{1}/{2}";//发起请求,直接返回对象（restful风格）ResponseBean responseBean = restTemplate.getForObject(url, ResponseBean.class, "001", "张三");System.out.println(responseBean.toString());
}

@Autowired
private RestTemplate restTemplate;/*** 单元测试（带参的get请求）*/
@Test
public void testGetByParam(){//请求地址String url = "http://localhost:8080/testGetByParam?userName={userName}&userPwd={userPwd}";//请求参数Map<String, String> uriVariables = new HashMap<>();uriVariables.put("userName", "唐三藏");uriVariables.put("userPwd", "123456");//发起请求,直接返回对象（带参数请求）ResponseBean responseBean = restTemplate.getForObject(url, ResponseBean.class, uriVariables);System.out.println(responseBean.toString());
}

3、文件上传

@Autowired
private RestTemplate restTemplate;/*** 文件上传，post请求*/
@Test
public void upload(){//需要上传的文件String filePath = "/Users/panzhi/Desktop/Jietu20220205-194655.jpg";//请求地址String url = "http://localhost:8080/upload";// 请求头设置,multipart/form-data格式的数据HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.MULTIPART_FORM_DATA);//提交参数设置MultiValueMap<String, Object> param = new LinkedMultiValueMap<>();param.add("uploadFile", new FileSystemResource(new File(filePath)));//服务端如果接受额外参数，可以传递param.add("userName", "张三");// 组装请求体HttpEntity<MultiValueMap<String, Object>> request = new HttpEntity<>(param, headers);//发起请求ResponseBean responseBean = restTemplate.postForObject(url, request, ResponseBean.class);System.out.println(responseBean.toString());
}

4、文件下载

@Autowired
private RestTemplate restTemplate;/*** 小文件下载* @throws IOException*/
@Test
public void downloadFile() throws IOException {String userName = "张三";String fileName = "c98b677c-0948-46ef-84d2-3742a2b821b0.jpg";//请求地址String url = "http://localhost:8080/downloadFile/{1}/{2}";//发起请求,直接返回对象（restful风格）ResponseEntity<byte[]> rsp = restTemplate.getForEntity(url, byte[].class, userName,fileName);System.out.println("文件下载请求结果状态码：" + rsp.getStatusCode());// 将下载下来的文件内容保存到本地String targetPath = "/Users/panzhi/Desktop/"  + fileName;Files.write(Paths.get(targetPath), Objects.requireNonNull(rsp.getBody(), "未获取到下载文件"));
}