RestTemplate最佳实践

一 介绍

RestTemplate 是Spring提供的一个用于http访问的工具模板

二 依赖

使用restTemplate需要导入如下pom依赖

<!--restTemplate启动器-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<!--根据需要导入httpcomponents-->
<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
  <version>4.5.10</version>
</dependency>

三 restTemplate配置

在使用restTemplate之前 还需要简单的对restTemplate进行配置 配置类如下

@Data
@Configuration
@ConfigurationProperties(prefix = "xx.xx.xx")
public class RestTemplateConfig {

    private Long connectionTimeout = 1000L;

    private Long readTimeout = 1000L;

    @Bean //将RestTemplate装配为bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder
                .requestFactory(HttpComponentsClientHttpRequestFactory.class)
                .setConnectTimeout(Duration.ofMillis(connectionTimeout))  //设置http的链接超时时间
                .setReadTimeout(Duration.ofMillis(readTimeout)) //设置http的响应超时时间
                .build();
    }
}

四 使用restTemplate

@RestController
public class TestController {

    @Autowired
    private RestTemplate restTemplate;

   /**
    * 获取nacos中指定dataId的配置信息
    **/
    @RequestMapping(path = "/getConfig", method = RequestMethod.GET)
    public String getConfig(HttpServletRequest request) {
        //获取nacos的accessToken
        String accessToken = getAccessToken();
        accessToken = String.valueOf(JSON.parseObject(accessToken, Map.class).get("accessToken"));

        String url = "http://xxxx/nacos/v1/cs/configs?dataId={dataId}&group={group}&tenant={tenant}&accessToken={accessToken}&namespaceId={namespaceId}";
        Map<String, Object> paramMap = new HashMap<String, Object>();
        paramMap.put("dataId","xxx");
        paramMap.put("group","DEFAULT_GROUP");
        paramMap.put("tenant","xx");
        paramMap.put("accessToken", accessToken);
        paramMap.put("namespaceId","xxx");

                //设置请求头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

        HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<>(null, headers);
        ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.GET, entity, String.class, paramMap);
        return response.getBody();
    }
  
  /**
    * 获取nacos的accessToken
    **/
  private String getAccessToken() {
        String url = "http://xxx/nacos/v1/auth/login";
        MultiValueMap<String, Object> paramMap = new LinkedMultiValueMap<String, Object>();
        paramMap.add("username","nacos");
        paramMap.add("password","nacos");

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); //请求类型为表单

        HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<>(paramMap, headers);
        ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
        return response.getBody();
    }
}

五 发送POST请求

使用RestTemplate post请求的时候主要可以通过三种方式实现

• 调用postForObject方法
• 调用postEntity方法
• 调用exchange方法

postForObject和postForEntity方法的区别主要在于可以在postForEntity方法中设置header的属性，当需要指定header的属性值的时候，使用postForEntity方法。exchange方法和postForEntity类似，但是更灵活，exchange还可以调用get、put、delete请求。

ContentType是表单

当ContentType的类型为表单类型时(content-type=application/x-www-form-urlencoded等)post请求的body不能是json也不能是map必须是MultiValueMap类型

private String getAccessToken() {
  String url = "http://xxx/nacos/v1/auth/login";
  //因为ContentType是表单 所以用MultiValueMap去对表单进行设值
  MultiValueMap<String, Object> paramMap = new LinkedMultiValueMap<String, Object>();
  paramMap.add("username","nacos");
  paramMap.add("password","nacos");

  HttpHeaders headers = new HttpHeaders();
  headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); //请求类型为表单 

  HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<>(paramMap, headers);
  ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
  return response.getBody();
}

ContentType是JSON

当ContentType是json的时候 就没有这么麻烦了 可以直接填充json格式的参数作为bo

@RequestMapping(path = "/test", method = RequestMethod.GET)
    public String test() {
        String url = "https://xxx/web/message/view/unread";
        Map<String, Object> paramMap = new HashMap<>();
        paramMap.put("coupon", true);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);  //设值contentType是application/json 
        headers.add("Cookie", "xxx");  //添加cookie
        HttpEntity<String> entity = new HttpEntity<>(JSON.toJSONString(paramMap), headers); //这里body被转换成了json
        ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
        return response.getBody();
    }

六 发送GET请求

restTemplate发送GET请求如果需要带参数 必须在url上填充占位符 示例如下

/**
    * 获取nacos中指定dataId的配置信息
    **/
    @RequestMapping(path = "/getConfig", method = RequestMethod.GET)
    public String getConfig(HttpServletRequest request) {
        //获取nacos的accessToken
        String accessToken = getAccessToken();
        accessToken = String.valueOf(JSON.parseObject(accessToken, Map.class).get("accessToken"));

        String url = "http://xxxx/nacos/v1/cs/configs?dataId={dataId}&group={group}&tenant={tenant}&accessToken={accessToken}&namespaceId={namespaceId}"; //注意这里url中的{xx}都是占位符
        Map<String, Object> paramMap = new HashMap<String, Object>();  //这里用map而不用MultiValueMap
        paramMap.put("dataId","xxx");
        paramMap.put("group","DEFAULT_GROUP");
        paramMap.put("tenant","xx");
        paramMap.put("accessToken", accessToken);
        paramMap.put("namespaceId","xxx");

                //设置请求头
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

        HttpEntity<MultiValueMap<String, Object>> entity = new HttpEntity<>(null, headers); //注意get请求时 这里填充的是null
        ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.GET, entity, String.class, paramMap);
        return response.getBody();
    }