SpringCloud | Part 3: Service Consumer (Feign)

1. Introduction to
Feign Feign is a declarative pseudo Http client, which makes it easier to write Http clients. With Feign, you just need to create an interface and annotate it. It has a pluggable annotation feature and can use Feign annotations and JAX-RS annotations. Feign supports pluggable encoders and decoders. Feign integrates Ribbon by default and combines with Eureka to achieve load balancing by default.

In short:
1. Feign uses interface-based annotations
2. Feign integrates ribbon

2. Preparations
Continue to use the project in the previous section, start eureka-server, the port is 8761; start service-hi twice, the port They are 8762 and 8773 respectively.

3. Create a feign service
Create a new spring-boot project named serice-feign, and introduce Feign's starting dependencies spring-cloud-starter-feign and Eureka into its pom file, spring-cloud-starter-feign, Eureka's starting dependencies spring -cloud-starter-eureka, Web start depends on spring-boot-starter-web, the code is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.forezp</groupId>
    <artifactId>service-feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>service-feign</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

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

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

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Dalston.RC1</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>
</project>

In the project configuration file application.yml file, specify the program name as service-feign, the port number as 8765, and the service registration address as http://localhost:8761/eureka/ , the code is as follows:

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8765
spring:
  application:
    name: service-feign

In the startup class ServiceFeignApplication of the program, add the @EnableFeignClients annotation to enable Feign's function:

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignApplication {

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

Define a feign interface, through @ FeignClient ("service name") , to specify which service to call. For example, the "/hi" interface of the service-hi service is called in the code, and the code is as follows:

@FeignClient(value = "service-hi")
public interface SchedualServiceHi {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam(value = "name") String name);
}

In the controller layer of the Web layer, an API interface of "/hi" is exposed to the outside, and the service is consumed through the Feign client ScheduleServiceHi defined above. code show as below:

@RestController
public class HiController {

    @Autowired
    SchedualServiceHi schedualServiceHi;
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    public String sayHi(@RequestParam String name){
        return schedualServiceHi.sayHiFromClientOne(name);
    }
}

Start the program, visit http://localhost:8765/hi?name=forezp multiple times, the browser will display alternately:

hi forezp,i am from port:8762
hi forezp,i am from port:8763


Feign source code analysis: http:/ /blog.csdn.net/forezp/article/details/73480304

from: http://blog.csdn.net/forezp/article/details/69808079