428 lines
12 KiB
Markdown
428 lines
12 KiB
Markdown
# Spring-Cloud-Feign
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<nav>
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<a href="#一Feign-简介">一、Feign 简介</a><br/>
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<a href="#二项目结构">二、项目结构</a><br/>
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<a href="#三服务提供者的实现">三、服务提供者的实现</a><br/>
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<a href="#31-定义服务">3.1 定义服务</a><br/>
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<a href="#32-服务注册">3.2 服务注册</a><br/>
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<a href="#四服务消费者的实现">四、服务消费者的实现</a><br/>
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<a href="#41-基本依赖">4.1 基本依赖</a><br/>
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<a href="#42-EnableFeignClients">4.2 @EnableFeignClients </a><br/>
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<a href="#43-创建服务调用接口">4.3 创建服务调用接口</a><br/>
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<a href="#44--Feign-客户端">4.4 Feign 客户端</a><br/>
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<a href="#45--调用远程服务">4.5 调用远程服务</a><br/>
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<a href="#五启动测试">五、启动测试</a><br/>
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<a href="#51-启动服务">5.1 启动服务</a><br/>
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<a href="#52--验证负载均衡">5.2 验证负载均衡</a><br/>
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<a href="#六Feign-的服务容错">六、Feign 的服务容错</a><br/>
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<a href="#61-开启容错配置">6.1 开启容错配置</a><br/>
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<a href="#62-定义降级处理">6.2 定义降级处理</a><br/>
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<a href="#63-配置降级处理">6.3 配置降级处理</a><br/>
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<a href="#64-测试熔断">6.4 测试熔断</a><br/>
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</nav>
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## 一、Feign 简介
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在上一个用例中，我们使用 Ribbon + RestTemplate 实现服务之间的远程调用，实际上每一个调用都是模板化的内容，所以 Spring Cloud Feign 在此基础上进行了进一步的封装。我们只需要定义一个接口并使用 Feign 注解的方式来进行配置，同时采用 springMvc 注解进行参数绑定就可以完成服务的调用。Feign 同时还内置实现了负载均衡、服务容错等功能。
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## 二、项目结构
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+ **common**：公共的接口和实体类；
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+ **consumer**：服务的消费者，采用 Feign 调用产品服务；
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+ **producer**：服务的提供者；
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+ **eureka**：注册中心。
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-feign.png"/> </div>
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## 三、服务提供者的实现
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/feign-producer.png"/> </div>
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### 3.1 定义服务
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产品服务由 `ProductService` 提供，并通过 `ProducerController` 将服务暴露给外部调用：
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ProductService.java：
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```java
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/**
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* @author : heibaiying
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* @description : 产品提供接口实现类
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*/
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@Service
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public class ProductService implements IProductService, ApplicationListener<WebServerInitializedEvent> {
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private static List<Product> productList = new ArrayList<>();
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public Product queryProductById(int id) {
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return productList.stream().filter(p->p.getId()==id).collect(Collectors.toList()).get(0);
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}
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public List<Product> queryAllProducts() {
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return productList;
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}
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@Override
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public void saveProduct(Product product) {
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productList.add(product);
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}
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@Override
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public void onApplicationEvent(WebServerInitializedEvent event) {
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int port = event.getWebServer().getPort();
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for (long i = 0; i < 20; i++) {
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productList.add(new Product(i, port + "产品" + i, i / 2 == 0, new Date(), 66.66f * i));
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}
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}
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}
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```
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ProducerController.java：
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```java
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@RestController
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public class ProducerController implements ProductFeign {
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@Autowired
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private IProductService productService;
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@GetMapping("products")
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public List<Product> productList() {
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return productService.queryAllProducts();
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}
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@GetMapping("product/{id}")
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public Product productDetail(@PathVariable int id) {
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return productService.queryProductById(id);
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}
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@PostMapping("product")
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public void save(@RequestBody Product product) {
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productService.saveProduct(product);
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}
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}
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```
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### 3.2 服务注册
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指定注册中心地址,并在启动类上开启自动注册 @EnableDiscoveryClient：
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```java
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server:
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port: 8020
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# 指定服务命名
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spring:
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application:
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name: producer
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# 指定注册中心地址
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eureka:
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client:
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serviceUrl:
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defaultZone: http://localhost:8010/eureka/
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```
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```java
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@SpringBootApplication
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@EnableDiscoveryClient
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public class ProducerApplication {
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public static void main(String[] args) {
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SpringApplication.run(ProducerApplication.class, args);
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}
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}
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```
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## 四、服务消费者的实现
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/feign-consumer.png"/> </div>
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### 4.1 基本依赖
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```xml
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<!-- feign 依赖-->
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-starter-openfeign</artifactId>
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</dependency>
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```
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### 4.2 @EnableFeignClients
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指定注册中心地址，并在启动类上添加注解 @EnableDiscoveryClient 和 @EnableFeignClients，@EnableFeignClients 会去扫描工程中所有用 @FeignClient 声明的 Feign 客户端：
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```java
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server:
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port: 8080
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# 指定服务命名
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spring:
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application:
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name: consumer
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# 指定注册中心地址
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eureka:
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client:
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serviceUrl:
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defaultZone: http://localhost:8010/eureka/
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```
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```java
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@SpringBootApplication
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@EnableDiscoveryClient
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@EnableFeignClients
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public class ConsumerApplication {
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public static void main(String[] args) {
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SpringApplication.run(ConsumerApplication.class, args);
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}
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}
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```
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### 4.3 创建服务调用接口
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```java
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/**
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* @author : heibaiying
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* @description : 声明式服务调用
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*/
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public interface ProductFeign {
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@GetMapping("products")
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List<Product> productList();
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/**
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* 这是需要强调的是使用 feign 时候@PathVariable 一定要用 value 指明参数，
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* 不然会抛出.IllegalStateException: PathVariable annotation was empty on param 异常
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*/
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@GetMapping("product/{id}")
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Product productDetail(@PathVariable(value = "id") int id);
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@PostMapping("product")
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void save(@RequestBody Product product);
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}
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```
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按照官方对于服务最佳化的推荐，这里我们的服务调用接口放在公共模块中，因为在实际的开发中，同一个服务调用接口可能被多个模块所使用。
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/common-feign.png"/> </div>
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### 4.4 Feign 客户端
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继承公共接口，创建 CProductFeign， 用 @FeignClient 声明为 Feign 客户端：
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```java
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/**
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* @author : heibaiying
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* @description : 声明式接口调用
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*/
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@FeignClient(value = "producer",configuration = FeignConfig.class)
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public interface CProductFeign extends ProductFeign {
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}
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```
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### 4.5 调用远程服务
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注入并使用 Feign 接口调用远程服务：
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```java
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@Controller
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@RequestMapping("sell")
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public class SellController {
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@Autowired
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private CProductFeign cproductFeign;
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@GetMapping("products")
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public String productList(Model model) {
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List<Product> products = cproductFeign.productList();
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model.addAttribute("products", products);
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return "products";
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}
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@GetMapping("product/{id}")
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public String productDetail(@PathVariable int id, Model model) {
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Product product = cproductFeign.productDetail(id);
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model.addAttribute("product", product);
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return "product";
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}
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@PostMapping("product")
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public String save(@RequestParam String productName) {
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long id = Math.round(Math.random() * 100);
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Product product = new Product(id, productName, false, new Date(), 88);
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cproductFeign.save(product);
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return "redirect:products";
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}
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}
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```
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## 五、启动测试
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### 5.1 启动服务
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启动一个Eureka服务、三个生产者服务（注意区分端口）、和一个消费者服务。Feign 的依赖中导入了 spring-cloud-starter-netflix-ribbon 依赖，并且在内部实现了基于 Ribbon 的客户端负载均衡，所以我们这里启动三个生产者服务来观察负载均衡的情况：
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-ribbon-app.png"/> </div>
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**服务注册中心：**
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-ribbon-eureka.png"/> </div>
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### 5.2 验证负载均衡
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访问 http://localhost:8080/sell/products 查看负载均衡的调用结果：
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-ribbon-products-8020.png"/> </div>
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-ribbon-products-8030.png"/> </div>
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/feign-8040.png"/> </div>
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## 六、Feign 的服务容错
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### 6.1 开启容错配置
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Feign 的依赖中默认导入了 Hystrix （熔断器）的相关依赖，我们不需要额外导入，只需要开启相关配置即可：
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/feign-hystrix-maven.png"/> </div>
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在 application.yml 中开启 Hystrix ：
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```yml
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feign:
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hystrix:
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# 如果为 true，则 OpenFign 客户端将使用 Hystrix 断路器进行封装 默认为 false
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enabled: true
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```
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### 6.2 定义降级处理
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创建 `CProductFeignImpl`，继承 Feign接口（CProductFeign），定义熔断时候的降级处理机制：
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```java
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/**
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* @author : heibaiying
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* @description : 定义发生熔断时候的降级处理。除了继承自 CProductFeign,还需要用 @Component 声明为 spring 的组件
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*/
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@Component
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public class CProductFeignImpl implements CProductFeign {
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// 发生熔断时候，返回空集合，前端页面会做容错显示
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@Override
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public List<Product> productList() {
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return new ArrayList<>();
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}
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@Override
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public Product productDetail(int id) {
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return null;
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}
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@Override
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public void save(Product product) {
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}
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}
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```
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页面的简单容错处理：
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```html
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<!doctype html>
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<html lang="en">
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<head>
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<title>产品列表</title>
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</head>
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<body>
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<h3>产品列表:点击查看详情</h3>
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<form action="/sell/product" method="post">
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<input type="text" name="productName">
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<input type="submit" value="新增产品">
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</form>
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<ul>
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<#if (products?size>0) >
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<#list products as product>
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<li>
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<a href="/sell/product/${product.id}">${product.name}</a>
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</li>
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</#list>
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<#else>
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<h4 style="color: red">当前排队人数过多，请之后再购买！</h4>
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</#if>
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</ul>
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</body>
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</html>
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```
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### 6.3 配置降级处理
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在 @FeignClient 注解中，用 fallback 参数指定熔断时候的降级处理：
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```java
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/**
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* @author : heibaiying
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* @description : 声明式接口调用
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*/
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@FeignClient(value = "producer",configuration = FeignConfig.class,fallback = CProductFeignImpl.class)
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public interface CProductFeign extends ProductFeign {
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}
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```
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### 6.4 测试熔断
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Hystrix 默认调用超时时间为 2s ，这里我们使用线程休眠的方式来模拟超时熔断。
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```java
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public List<Product> queryAllProducts() {
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/*用于测试 hystrix 超时熔断
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try {
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int i = new Random().nextInt(2500);
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Thread.sleep(i);
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} catch (InterruptedException e) {
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e.printStackTrace();
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}*/
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return productList;
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}
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```
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测试结果：
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/feign-hystrix.png"/> </div>
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