Microservice practice | declarative service invocation openfeign practice

Last one Micro service practice | Load balancing components and source code analysis

OpenFeign Introduce

In limine , We use native DiscoveryClient Discover services and use RestTemplate Make calls between services , Then we manually developed a load balancing component , Finally, the load balancing component is introduced Ribbon. Each chapter invokes services in different ways , The common ground is that they are all based on RestTemplate To achieve , Presumably, everyone will find this calling method a little troublesome , Write the request protocol before each call , The service name , The name of the interface 、 Assembly parameters 、 Processing response data types , These are all repetitive tasks , The code is also highly similar , Only URL Different , The request method is different 、 Different parameters , Everything else is basically the same , In that case , Is there any way to simplify the request ？ In this article, we will talk about declarative microservice invocation OpenFeign .

OpenFeign Is a display declarative WebService client . Use OpenFeign Can make writing Web Service The client is simpler . When using, you only need to define the service interface , Then add comments on it .OpenFeign It also supports pluggable encoders and decoders .spring cloud Yes feign It was packaged , To support MVC Notes and HttpMessageConverts. and eureka（ Service registry ） and ribbon Combination can realize load balancing . stay Spring Cloud Use in OpenFeign, It can be used HTTP Request access to remote services , It's like calling a local method , Developers are totally unaware that this is a call to a remote method , More imperceptible in the visit HTTP request , Very convenient

• OpenFeign Design purpose based simplification Java Http Client development .Feign stay restTemplate Further encapsulation is made on the basis of , It helps us define and implement the definition of dependent service interfaces . stay OpenFeign With the help of , We just need to create an interface and configure it with annotations （ Be similar to Dao On the interface Mapper annotation ） You can complete the interface binding to the service provider , Greatly simplified Spring cloud Ribbon Development of , Development volume of auto encapsulation service calling client .
• OpenFeign Integrated Ribbon, utilize ribbon Maintained service list , And through ribbon The load balancing of the client is realized . And ribbon The difference is , adopt OpenFeign Just define the service binding interface and use the declarative method , Elegant and simple implementation of service invocation .

Project practice

Create project

Next , Start our project practice , Create two services , One is dms（ It is the code meter service , Provide various drop-down options ）, One is application system app（ The actual business system ）

First create the name dms Of maven project , Introduce dependencies

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

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

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

    </dependencies>

create profile ：

server:
  port: 8003
spring:
  application:
    name: dms

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8001/eureka/

logging:
  pattern:
    console: '%d{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%thread] %logger{15} - %msg%n'

Write the startup class

/** * @Author: official account ： The programmer 965 * @create 2022-06-20 **/
@EnableDiscoveryClient
@EnableFeignClients
@EnableEurekaClient
@SpringBootApplication
public class DmsApplication {
    
    public static void main(String[] args) {
    
        SpringApplication.run(DmsApplication.class, args);
    }
}

Note that this time , We added @EnableFeignClients and @EnableDiscoveryClient annotation .

To write api Module code , Note that this is an interface to provide external services , The service name of the interface is dms, according to code Code value get name ：

/** * @Author: official account ： The programmer 965 * @create 2022-06-20 **/
@FeignClient(value = "dms")
public interface DmsApi {
    
    @RequestMapping(value="/dict/{code}", method = RequestMethod.GET)
    public String findNameByCode(@PathVariable("code") String code);
}

To write controller class , Can achieve DmsApi Interface , Here is a simple example of gender ：

/** * @Author: official account ： The programmer 965 * @create 2022-06-20 **/
@RestController
public class DmsController implements DmsApi {
    

    @Override
    public String findNameByCode(String code) {
    
        switch (code){
    
            case "0" :
                return " male ";
            case "1" :
                return " Woman ";
            default:
                return " Unknown ";
        }
    }
}

dms The module is developed .

alike , establish app modular , Note the need to introduce dms modular , In order to call its interface

<dependencies>

        <dependency>
            <groupId>com.cxy965</groupId>
            <artifactId>dms</artifactId>
            <version>${project.version}</version>
        </dependency>

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

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
        </dependency>

    </dependencies>

establish controller layer ： Inject here dmsApi, And pass dmsApi Call its findNameByCode() Method , You can complete the calling code of the service ！

/** * @Author: official account ： The programmer 965 * @create 2022-06-20 **/
@RestController
public class AppController {
    
    @Autowired
    private DmsApi dmsApi;

    @RequestMapping("/index")
    public String index(){
    
        String nameByCode = dmsApi.findNameByCode("1");
        return nameByCode;
    }

}

Start class

/** * @Author: official account ： The programmer 965 * @create 2022-06-20 **/
@EnableEurekaClient
@SpringBootApplication
public class AppApplication {
    
    public static void main(String[] args) {
    
        SpringApplication.run(AppApplication.class, args);
    }
}

Start project validation

Returned the correct result , When there are multiple registration centers dms The service , When called, it will automatically play the role of load balancing .

summary

OpenFeign yes Spring Cloud A member of the family , Its core function is to HTTP Formal Rest API It provides a very simple and efficient RPC Call mode . if Spring Cloud Other members address system level availability , Scalability issues , that OpenFeign It solves the development efficiency problem that is most closely related to the interests of developers . In this article, we learned Feign Integration and basic use of components , The next article will write Feign More use of , Let's hope together ！