以json的形式发送请求体，通过httpentity获取请求

import org.springframework.http.*;
import org.springframework.web.client.RestTemplate;

// 创建一个RestTemplate对象
RestTemplate restTemplate = new RestTemplate();

// 创建一个包含JSON数据的请求体
String jsonBody = "{\"name\": \"John\", \"age\": 30}";

// 创建HttpHeaders对象，并设置Content-Type为application/json
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);

// 创建HttpEntity对象，并设置请求体和头部信息
HttpEntity<String> requestEntity = new HttpEntity<>(jsonBody, headers);

// 发送POST请求，并获取响应
ResponseEntity<String> responseEntity = restTemplate.exchange("http://example.com/api", HttpMethod.POST, requestEntity, String.class);

// 获取响应的内容、状态码等
String responseBody = responseEntity.getBody();
HttpStatus statusCode = responseEntity.getStatusCode();
// ...