REST POST 与 POSTMAN 一起工作正常，但使用 Spring RestTemplate 时出现异常

使用REST POST与POSTMAN工作正常，但在使用Spring RestTemplate时出现异常

java
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;
public class RestTemplateExample {
    public static void main(String[] args) {
        String url = "https://example.com/api";
        
        // 设置请求头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        
        // 设置请求参数
        MultiValueMap params= new LinkedMultiValueMap<>();
        params.add("username", "admin");
        params.add("password", "123456");
        // 创建请求实体
        HttpEntity> request = new HttpEntity<>(params, headers);
        // 创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();
        try {
            // 发送POST请求
            ResponseEntity response = restTemplate.postForEntity(url, request, String.class);
            
            // 处理响应
            if (response.getStatusCode().is2xxSuccessful()) {
                String responseBody = response.getBody();
                System.out.println("Response: " + responseBody);
            } else {
                System.out.println("Request failed with status code: " + response.getStatusCodeValue());
            }
        } catch (Exception e) {
            System.out.println("Exception occurred: " + e.getMessage());
        }
    }
}