如何使用Spring的RestTemplate发送自定义对象和headers

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

public class User {
    private String name;
    private int age;
    // 省略getter和setter方法
}

RestTemplate restTemplate = new RestTemplate();

String url = "http://example.com/api/user";
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);

User user = new User();
user.setName("John");
user.setAge(25);

HttpEntity<User> requestEntity = new HttpEntity<>(user, headers);
ResponseEntity<String> responseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class);