Spring Cloud Ribbon -- 服务负载均衡

Spring Cloud Ribbon：封装于Netflix Ribbon， [ˈrɪbən]，带状物
功能：负载均衡（服务选取）
原理：@LoadBalanced、@FeignClient 底层都调用了Ribbon组件

服务调用之 RestTemplate

方式一：使用 LoadBalancerClient 选取服务实例

@Autowired
private LoadBalancerClient lbc;  // Eureka Client 应用的容器中 有 这个 Bean

RestTemplate rt = new RestTemplate();
ServiceInstance si = lbc.choose("SERVICE_NAME");  // 选取服务实例
String url = String.format("http://%s:%s",si.getHost(), si.getPort()) + "/api";
String response = rt.getForObject(url, String.class);   // 使用RestTemplate 调用服务

方式二：使用 @LoadBalanced 选取服务实例
1、装配 RestTemplate

@Component
public class RestTemplateConfig {
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate(){
        SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
        requestFactory.setConnectTimeout(60*60*1000);   // 提交超时时间
        requestFactory.setReadTimeout(60*60*1000);   // 下载超时时间

        RestTemplate restTemplate = new RestTemplate(requestFactory);
        restTemplate.getMessageConverters().add(new FastJsonHttpMessageConverter());  // 格式转换器
        restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8));
        return restTemplate;
    }
}

2、使用

@Autowired
private RestTemplate restTemplate;

/* Get请求 */
// 得到对象，Response 为自定义的POJO；要求response body 得是JSON格式，否则 Response 只能是 String
Response response = restTemplate.getForObject(url, Response.class); 
// 得到Entity，包含response header 和 response body，其中body被转换成 Response 实例
ResponseEntity<Response> responseEntity = restTemplate.getForEntity(url, Response.class); 
// 无论response body是什么格式，都可以用String来接
String response = restTemplate.getForObject(url, String.class); 

/* Get请求 带header */
HttpHeaders headers = new HttpHeaders();
HttpEntity requestEntity = new HttpEntity(null, headers);
ResponseEntity<Response> responseEntity = restTemplate.exchange(user_url, HttpMethod.GET, requestEntity, Response.class);
Response response = responseEntity.getBody();

/* Post请求，提交表单格式 */
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); 
MultiValueMap<String, String> map= new LinkedMultiValueMap();
map.add("filed_1", "**");
HttpEntity<MultiValueMap<String, String>> requestEntity = new HttpEntity(map, headers);
// 发送MultiValueMap，得到对象，同getForObject
Response response = restTemplate.postForObject(url, requestEntity, Response.class);
// 得到Entity，同getForEntity
ResponseEntity<Response> responseEntity = restTemplate.postForEntity(url, requestEntity, Response.class);

/* Post请求，提交JSON格式 */
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON); 
// 可以明确指定 Accept
List<MediaType> acceptList = new ArrayList<>(1);
acceptList.add(MediaType.APPLICATION_JSON);
headers.setAccept(acceptList); 
// 发送 HttpEntity 包装的 ObjectNode 字符串
ObjectNode objectNode = new ObjectMapper().createObjectNode();
objectNode.put("field_1", "**");
 HttpEntity<String> requestEntity = new HttpEntity(objectNode.toString(), headers);
 Response response = restTemplate.postForObject(url, requestEntity, Response.class);
// 或者 发送 HttpEntity 包装的 POJO实例
HttpEntity requestEntity = new HttpEntity(request, headers);
 Response response = restTemplate.postForObject(url, requestEntity, Response.class);
// 或者 直接发送POJO实例，默认的 content-type 就是 application/json
 Response response = restTemplate.postForObject(url, request, Response.class);

/*Post请求，提交XML格式*/
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_XML);
HttpEntity<String> requestEntity = new HttpEntity<>(xml, headers);
// 发送 xml 字符串
ResponseEntity<Response> responseEntity = restTemplate.postForObject(url, requestEntity, Response.class);

服务调用之 OpenFein

1、配置Maven依赖

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
            <version>2.0.2.RELEASE</version> <!-- 与Spring Cloud版本不同，需要指明版本 -->
        </dependency>

2、注解主类：@EnableFeignClients
3、定义Fein Client 接口

@FeignClient(name= "Eureka-Client")  // 服务名不支持下划线
public interface Client {
    // 与Controller里的写法相同
    @GetMapping("/my/send2")  // @GetMapping相当于@RequestMapping( method=RequestMethod.GET)

    String getMsg();
}

4、调用

@Autowired
private Client client;

String response = client.getMsg();

负载均衡算法

配置 application.yml

SERVICE_NAME:
    ribbon:
        NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule # 默认为轮询，这里改成随机

ribbon负载均衡算法实现类查找方法：IRule 的实现类