spring cloud : 简化远程调用 （声明式远程调用Feign）

场景：在controller中调用service的方法，在service的方法中远程调用。

好处：原来的写法要将url中的参数重新在controller中封装成一个map或者对象传递给restTemplate对象， restTemplate对象再解析这个map或者对象 =》消除这个封装的过程。

1.     单一返回值

1.     添加依赖

<dependency>             <groupId>org.springframework.cloud</groupId>             <artifactId>spring-cloud-starter-feign</artifactId>         </dependency>

2.     添加远程调用接口

package com.svw.tbox.tcloud.user.consumer.api; import java.util.List; import org.springframework.cloud.netflix.feign.FeignClient; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import com.svw.tbox.tcloud.user.consumer.entity.User; @FeignClient(name = "tcloud-user-provider") publicinterface UserFeignClient {   @RequestMapping(value = "/likeName/{name}", method = RequestMethod.GET)   public List<User> findByName(@PathVariable("name") String name); }

3.     改造controller

package com.svw.tbox.tcloud.user.consumer.controller; import java.util.List; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.cloud.client.ServiceInstance; import org.springframework.cloud.client.loadbalancer.LoadBalancerClient; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController; import com.svw.tbox.tcloud.user.consumer.entity.User; import com.svw.tbox.tcloud.user.consumer.feign.UserFeignClient; @RestController publicclass TboxController {     privatestaticfinal Logger LOGGER = LoggerFactory.getLogger(TboxController.class);     @Autowired     private LoadBalancerClient loadBalancerClient;     @GetMapping("/log-instance")     public String logUserInstance(){         ServiceInstance serviceInstance=this.loadBalancerClient.choose("tcloud-user-provider");         //打印当前选择的是哪个节点         TboxController.LOGGER.info("{}:{}:{}",serviceInstance.getServiceId(),serviceInstance.getHost(),serviceInstance.getPort());         return"hello";     }     @Autowired     private UserFeignClient userFeignClient;     @GetMapping("/user/{name}")     public List<User> likeName(@PathVariable String name){         returnuserFeignClient.findByName(name); //      return this.restTemplate.getForObject("http://localhost:8000/likeName/"+name, List.class) ;     } }

4.     启动类开启Feign

@SpringBootApplication @EnableDiscoveryClient @EnableFeignClients publicclass ConsumerApplication { …

5.     效果：

启动eureka server两个实例

启动tcloud-user-provider两个实例

启动tcloud-user-consumer

多次访问http://localhost:9000/user/hrf

两个provider控制台打印查询数据库命令（开启sql显示命令）

2.     多个多种类型的返回值

1.     调用方

Map<String,Object> reMap =gatewayAuthService.isThrereARightToAccessAndGetUserInfo(accessToken, requestUri, method); boolean isAccessTokenExistInRedis = (boolean) reMap.get("isAccessTokenExistInRedis"); Map<String, Object> userInfo = (LinkedHashMap<String, Object>)reMap.get("userInfo");

public Map<String,Object> isThrereARightToAccessAndGetUserInfo(String accessToken, String requestUri, String method) {        Map<String,String> map = new HashMap<>();        map.put("accessToken", accessToken);        map.put("requestUri", requestUri);        map.put("method", method);        returnauthFeignClient.isThrereARightToAccessAndGetUserInfo(map);     }

@FeignClient(name = "tcloud-security-auth") publicinterface AuthFeignClient {     @RequestMapping(value = "/tokenAuth/isThrereARightToAccessAndGetUserInfo", method = RequestMethod.GET)     public Map<String,Object> isThrereARightToAccessAndGetUserInfo(@RequestParam Map<String,String> map); }

publicclass AuthFeignClientFallback implements AuthFeignClient {     @Override     public Map<String,Object> isThrereARightToAccessAndGetUserInfo(Map<String, String> map) {        Map<String,Object> remap = new HashMap<>();        remap.put("isAccessTokenExistInRedis", false);        remap.put("isUserInfoExists", false);        remap.put("isThrereARightToAccess", false);        remap.put("userInfo", new LinkedHashMap<>());        returnremap;     } }

2.     生产方

@RestController @RequestMapping("/tokenAuth") publicclass TokenController {     @Autowired     private TokenService tokenService;     @RequestMapping(value = "/isThrereARightToAccessAndGetUserInfo", method = RequestMethod.GET)     public Map<String,Object> isThrereARightToAccessAndGetUserInfo(@RequestParam Map<String,String> map) {        String accessToken = map.get("accessToken");        String requestUri = map.get("requestUri");        String method = map.get("method");        returntokenService.isThrereARightToAccessAndGetUserInfo(accessToken,requestUri,method);     } }

public Map<String,Object> isThrereARightToAccessAndGetUserInfo(String accessToken, String requestUri, String method) {        Map<String,Object> reMap = new HashMap<>();        if(!checkAccessTokenExistInRedis(accessToken)) {            reMap.put("isAccessTokenExistInRedis", false);        }else {……            if(uv==null) { ……            }else {               reMap.put("userInfo", uv);               reMap.put("isUserInfoExists", true);            } ……     reMap.put("isThrereARightToAccess" ,true);        }        returnreMap;     }