SpringCloud (2): Declarative RestClient—Feign

 (It is not easy to write, please indicate when reprinting: http://shihlei.iteye.com/blog/2399457 )

 

I. Overview

 

        feign: A declarative rest client, spring cloud extends feign, provides springmvc tag support, and replaces RestTemplate to simplify operations.

        git：https://github.com/OpenFeign/feign

 

Two items

 

        Service Provider: Time Microservice in "SpringCloud (1): SpringBoot Creates Simple Microservices" - spring-cloud-microservice

        Service consumer: "SpringCloud (1): SpringBoot creates a simple microservice" improvement - TimeService implementation in spring-cloud-webfront 

 

Three code implementation

(1) Add dependencies

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

 

(2) Resource file adding time microservice server configuration:

server:
  port: 20001

# custom configuration
timeMisroService:
  server: http://localhost:10001

 

 

(3) Define the feign interface

package x.demo.springcloud.webfront.service.impl.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import x.demo.springcloud.webfront.service.impl.ProtocolResult;

@FeignClient(name = "microservice-time", url = "${timeMisroService.server}")
public interface TimeV1MicroServiceClient {

    @RequestMapping(method = RequestMethod.GET, value = "/time/v1/now", consumes = MediaType.APPLICATION_JSON_VALUE)
    ProtocolResult<String> now(@RequestParam(name = "format", required = false) String format);
}

 

(4) Implement TimeService

package x.demo.springcloud.webfront.service;

public interface TimeService {
    /**
     * Get current time
     * @return current time, format: yyyy-MM-dd HH:mm:ss
     */
    String now();
}

 

package x.demo.springcloud.webfront.service.impl;

import javax.annotation.Resource;

import org.springframework.stereotype.Service;
import x.demo.springcloud.webfront.service.TimeService;
import x.demo.springcloud.webfront.service.impl.feign.TimeV1MicroServiceClient;

@Service("timeV1FeignImpl")
public class TimeV1FeignImpl implements TimeService {

    @Resource
    private TimeV1MicroServiceClient timeV1MicroServiceClient;

    /**
     * Get current time
     *
     * @return current time, format: yyyy-MM-dd HH:mm:ss
     */
    @Override
    public String now() {
        ProtocolResult<String> result = timeV1MicroServiceClient.now(null);
        return result.getBody();
    }
}

(5) The controller calls the service

 

package x.demo.springcloud.webfront.web;

import javax.annotation.Resource;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import x.demo.springcloud.webfront.service.TimeService;

@RestController
@RequestMapping("/time")
public class TimeController {

    @Resource(name = "timeV1FeignImpl")
    private TimeService timeService;

    @GetMapping("/now")
    public String now() {
        return timeService.now();
    }
}

 

 

(6) Enable FeignClient support: mainly add @EnableFeignClients for Spring Cloud generation implementation

 

package x.demo.springcloud.webfront;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class SpringCloudWebfrontApplication {

	public static void main(String[] args) {
		SpringApplication.run(SpringCloudWebfrontApplication.class, args);
	}
}

   

(7) Effect: same as the previous article

4. Use feign in common projects

Difference: because there is no spring cloud instance FeignClient, you can only instantiate FeignClient yourself

 

package x.demo.springcloud.webfront.conf;

import feign.Feign;
import feign.Request;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.netflix.feign.support.SpringMvcContract;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;
import x.demo.springcloud.webfront.service.impl.feign.TimeV1MicroServiceClient;

@Configuration
public class SpringConfiguration {

    @Value("${timeMisroService.server}")
    private String timeMisroServiceServer;

    @Bean
    public TimeV1MicroServiceClient timeV1MicroServiceClient() {
        return Feign.builder()
                .encoder(new GsonEncoder())
                .decoder(new GsonDecoder())
                .contract(new SpringMvcContract())
                .options(new Request.Options(5000, 5000))
                .target(TimeV1MicroServiceClient.class, timeMisroServiceServer);
    }

}

 

Five other

(1) feign currently does not support Mvc annotation @GetMapping @PostMapping will report an error

 

(2) Provide json serialization support

rely:

        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-gson</artifactId>
        </dependency>