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声明式客户端OpenFeign(一)：基础应用

树下的老石头 2021-09-21 阅读 60
微服务Spring ...

OpenFeign简介

OpenFeign是一个声明式RESTful网络请求客户端。OpenFeign会根据带有注解的函数信息构建出网络请求的模板，在发送网络请求之前，OpenFeign会将函数的参数值设置到这些请求模板中。虽然OpenFeign只能支持基于文本的网络请求，但是它可以极大简化网络请求的实现，方便编程人员快速构建自己的网络请求应用。

如图所示，使用OpenFeign的Spring应用架构一般分为三个部分，分别为服务注册中心、服务提供者和服务消费者。服务提供者向服务注册中心注册自己，然后服务消费者通过OpenFeign发送请求时，OpenFeign会向服务注册中心获取关于服务提供者的信息，然后再向服务提供者发送网络请求。


代码示例

1. 服务注册中心control-eureka-server

OpenFeign可以配合Eureka等服务注册中心同时使用。Eureka作为服务注册中心，为OpenFeign提供服务端信息的获取，比如说服务的IP地址和端口。

参见：https://www.jianshu.com/p/9223970fc59c

2. 服务提供者control-user

Spring Cloud OpenFeign是声明式RESTful网络请求客户端，所以对服务提供者的实现方式没有任何影响。也就是说，服务提供者只需要提供对外的网络请求接口就可，至于其具体实现既可以使用Spring MVC，也可以使用Jersey。只需要确保该服务提供者被注册到服务注册中心上即可。

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ljessie</groupId>
    <artifactId>control-user</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>control-user</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Hoxton.SR4</spring-cloud.version>
    </properties>

    <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.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</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>

</project>

application.yml

eureka:
  instance:
    instance-id: server:1
  client:
    service-url: 
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8762
spring:
  application:
    name: userServer

TestController

@RestController
@RequestMapping("test")
public class TestController {
    @RequestMapping("test_feign")
    public String testFeign(String param){
        return "Hello "+param;
    }
}
3. 服务消费者control-personnel

pom.xml文件中添加Eureka和OpenFeign相关的依赖。

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.ljessie</groupId>
    <artifactId>control-personnel</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>control-personnel</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Hoxton.SR4</spring-cloud.version>
    </properties>

    <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> 

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</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>

</project>

application.yml

eureka:
  instance:
    hostname: personnel
    instance-id: ${spring.application.name}:${vcap.application.instance_id:${spring.application.instance_id:${random.value}}}
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8764
spring:
  application:
    name: personnelServer

入口类ControlPersonnelApplication添加@EnableFeignClients注解

package com.ljessie.controlpersonnel;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class ControlPersonnelApplication {

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

}

新建UserService接口访问消费提供者，类上面添加@FeignClient注解，参数为服务提供者application.yml里面注册的spring.application.name，RequestMapping参数即为服务提供者开放接口的路径。

package com.ljessie.controlpersonnel.service;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient("userServer")
public interface UserService {

    @RequestMapping("test/test_feign")
    String testFeign(@RequestParam("param")String param);
}

新建TestController，对外提供测试接口：

package com.ljessie.controlpersonnel.controller;

import com.ljessie.controlpersonnel.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("test")
public class TestController {

    @Autowired
    UserService userService;

    @RequestMapping("test_feign")
    public String testFeign(String param){
        return userService.testFeign(param);
    }

}

依次启动注册中心control-eureka-server，服务提供者control-user，服务消费者control-personnel。

访问http://localhost:8764/test/test_feign?param=Jessie

举报

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