Feign【入门】

2019-10-16 07:59:18来源：博客园阅读 ()

Feign【入门】

feign简介：

feign是一种声明式，模板化的HTTP客户端，spring cloud对feign进行了增强，使其支持SpringMvc的相关注解，并整合了ribbon做负载均衡。在spring cloud中使用feign做HTTP远程服务请求，可以做到就像调用本地方法一样，完全感知不到是在调用远程方法，具体特性如下：

可插拔的注解支持，包括feign注解和Jax-rs注解、
支持可插拔的HTTP编码器和解码器、
支持hystrix和它的fallback、
支持ribbon负载均衡、
支持HTTP请求和响应的压缩、

1、创建feign-demo工程

1.1、工程依赖

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.3.RELEASE</version>
        <relativePath/>
</parent>

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

<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>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <!-- Spring Cloud OpenFeign的Starter的依赖 -->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-openfeign</artifactId>
    </dependency>
</dependencies>

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

1.2、工程启动类：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class SpringCloudFeignApplication {

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

可以看到启动类上加了 @EnableFeignClients 注解，意思是当该工程在启动的时候，会进行包扫描，扫描该启动类包以下，子包中所有带 @FeignClient 注解的类（包括启动类所在包），并进行处理。

1.3、编写相关代码

HelloFeignService接口：

import cn.springcloud.book.feign.config.HelloFeignServiceConfig;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

//https://api.caiyunapp.com/v2/TAkhjf8d1nlSlspN/121.6544,25.1552/forecast.json 彩云天气API
@FeignClient(name = "caiyunapp", url = "https://api.caiyunapp.com/v2/TAkhjf8d1nlSlspN/121.6544,25.1552", configuration = HelloFeignServiceConfig.class)
public interface HelloFeignService {


    @RequestMapping(value = "/forecast.json", method = RequestMethod.GET)
    String searchRepo();

}

如上所示，@FeignClient注解手动指定了URL，最终会根据指定的URL和@RequestMapping对应的方法转换成完整的请求地址。如下：https://api.caiyunapp.com/v2/TAkhjf8d1nlSlspN/121.6544,25.1552/forecast.json

HelloFeignServiceConfig配置类：

import feign.Logger;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class HelloFeignServiceConfig {

    /**
     * Logger.Level 的具体级别如下：
     * NONE：不记录任何信息
     * BASIC：仅记录请求方法、URL以及响应状态码和执行时间
     * HEADERS：除了记录 BASIC级别的信息外，还会记录请求和响应的头信息
     * FULL：记录所有请求与响应的明细，包括头信息、请求体、元数据
     *
     * @return
     */
    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }

}

controller类：

import cn.springcloud.book.feign.service.HelloFeignService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloFeignController {

    @Autowired
    private HelloFeignService helloFeignService;

    // 服务消费者对位提供的服务
    @GetMapping(value = "/search")
    public String searchGithubRepoByStr(@RequestParam("str") String queryStr) {
        return helloFeignService.searchRepo(queryStr);
    }

}