一、介绍

RestTemplate 是 Spring 框架中用于发送 HTTP 请求的客户端工具类。它简化了与 REST 服务的交互，并提供了许多方法来发送 HTTP 请求，如 GET、POST、PUT、DELETE 等。

二、使用

1、添加依赖

如果你使用 Maven，确保你的项目中包含了 Spring Web 的依赖。

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

注意：这个依赖通常已经包含在 Spring Boot 的 web 应用程序的起步依赖中。

2、创建 RestTemplate 实例

在配置类中创建实例。

@Configuration  
public class AppConfig {  @Bean  public RestTemplate restTemplate() {  return new RestTemplate();  }  
}

或者使用 Spring Boot 2.0 之后的 RestTemplateBuilder 来创建它，这样可以更容易地进行自定义配置。

3、使用 RestTemplate

（1）GET请求

• 不带参数的get请求

@Service  
public class MyService {  private final RestTemplate restTemplate;  @Autowired  public MyService(RestTemplate restTemplate) {  this.restTemplate = restTemplate;  }  public String getDataFromRestService() {  String url = "http://example.com/api/data";  ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);  return response.getBody();  }  
}

• 带请求参数的get请求

@Service  
public class MyService {  private final RestTemplate restTemplate;  @Autowired  public MyService(RestTemplate restTemplate) {  this.restTemplate = restTemplate;  }  public String getDataFromRestService() {  String url = "http://example.com/api/data"; HttpHeaders headers = new HttpHeaders()// 设置后端请求Authorization认证headers.set("Authorization", "xxx");HttpEntity<Object> entity = new HttpEntity<>(authHeader);// 添加请求参数，最终的url为：http://example.com/api/data?pageNum=1&pageSize=10UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(url);builder.queryParam("pageNum", 1);builder.queryParam("pageSize", 10);ResponseEntity<Object> response = restTemplate.exchange(url, HttpMethod.GET, entity, Object.class);return response.getBody();  }  
}

• 带路径求情参数的get请求

@Service  
public class MyService {  private final RestTemplate restTemplate;  @Autowired  public MyService(RestTemplate restTemplate) {  this.restTemplate = restTemplate;  }  public String getDataFromRestService() {  String url = "http://example.com/api/data/{id}"; HttpHeaders headers = new HttpHeaders()// 设置后端请求Authorization认证headers.set("Authorization", "xxx");HttpEntity<Object> entity = new HttpEntity<>(authHeader);	// 设置路径参数Map<String, String> uriVariables = Collections.singletonMap("id", "123");// 添加请求参数，最终的url为：http://example.com/api/data?pageNum=1&pageSize=10UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(url);builder.queryParam("pageNum", 1);builder.queryParam("pageSize", 10);ResponseEntity<Object> response = restTemplate.exchange(url, HttpMethod.GET, entity, Object.class, uriVariables);return response.getBody();  }  
}

（2）POST请求

带认证的POST请求

@Service  
public class MyService {  private final RestTemplate restTemplate;  @Autowired  public MyService(RestTemplate restTemplate) {  this.restTemplate = restTemplate;  }  public String getDataFromRestService() {  String url = "http://example.com/api/data"; HttpHeaders headers = new HttpHeaders()// 设置后端请求Authorization认证headers.set("Authorization", "xxx");HttpEntity<Object> entity = new HttpEntity<>(authHeader);ResponseEntity<Object> response= restTemplate.postForEntity(url , entity, Object.class);return response.getBody();  }  
}