Spring Cloud 学习3. 声明式服务调用(Feign)

Feign是一个声明式的Web Service客户端，它的目的就是让Web Service调用更加简单。Feign提供了HTTP请求的模板，通过编写简单的接口和插入注解，就可以定义好HTTP请求的参数、格式、地址等信息。而Feign则会完全代理HTTP请求，我们只需要像调用方法一样调用它就可以完成服务请求及相关处理。

Feign整合了Ribbon和Hystrix(关于Hystrix我们后面再讲)，可以让我们不再需要显式地使用这两个组件。此外，Spring Cloud还对Feign提供了Spring MVC注解的支持，也使得我们在Web中可以使用同一个HttpMessageConverter。

Feign特征
- 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的负载均衡;
- 支持HTTP请求和响应的压缩。

demo

添加依赖：

<?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 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>twostepsfromjava.cloud</groupId>
        <artifactId>twostepsfromjava-cloud-parent</artifactId>
        <version>1.0.0-SNAPSHOT</version>
        <relativePath>../parent</relativePath>
    </parent>

    <artifactId>mall-web</artifactId>
    <name>Spring Cloud Sample Projects: Mall</name>

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

启动类

/**
 * TwoStepsFromJava Cloud -- Mall Web Project
 *
 * @author CD826(CD826Dong@gmail.com)
 * @since 1.0.0
 */
@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class Application {

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

}

接口调用类

/**
 * Product Service
 *
 * @author CD826(CD826Dong@gmail.com)
 * @since 1.0.0
 */
@FeignClient("PRODUCT-SERVICE")
public interface ProductService {

    @RequestMapping(value = "/products", method = RequestMethod.GET)
    List<Product> findAll();

    @RequestMapping(value = "/products/{itemCode}", method = RequestMethod.GET)
    Product loadByItemCode(@PathVariable("itemCode") String itemCode);

}

说明： 假如你的Service是单独编译一个jar包，那么在使用@EnableFeignClients注解时需要指定basePackages的值，如:

@EnableFeignClients(basePackages = "io.twostepsfromjava.cloud.**")
@EnableDiscoveryClient
@SpringBootApplication
public class Application {

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

}

controller

/**
 * Product Controller
 *
 * @author CD826(CD826Dong@gmail.com)
 * @since 1.0.0
 */
@RestController
@RequestMapping("/products")
public class ProductController {
    @Autowired
    private ProductService productService;

    @RequestMapping(method = RequestMethod.GET)
    public List<Product> list() {
        return this.productService.findAll();
    }

    @RequestMapping(value = "/{itemCode}", method = RequestMethod.GET)
    public Product detail(@PathVariable String itemCode) {
        return this.productService.loadByItemCode(itemCode);
    }
}

配置文件

server.port=8080

spring.application.name=MALL-WEB

eureka.client.service-url.defaultZone=http://localhost:8260/eureka

​

本文代码未测试。