283 lines
9.3 KiB
Markdown
283 lines
9.3 KiB
Markdown
# spring-cloud-ribbon
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## 一、ribbon 简介
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ribbon是Netfix公司开源的负载均衡组件，采用服务端负载均衡的方式，即消费者客户端维护可用的服务列表，并通过负载均衡的方式将请求按照指定的策略分摊给消费者，从而达到负载均衡的方式。
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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RestTemplate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，ribbon 从注册中心获取可用的服务列表，是实现负载均衡的基础。这里使用我们在[服务的注册与发现](https://github.com/heibaiying/spring-samples-for-all/tree/master/spring-cloud/spring-cloud-eureka)这个用例中搭建的简单注册中心作为测试即可。
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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/spring-cloud-ribbon.png"/> </div>
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## 三、服务提供者的实现
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#### 3.1 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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<div align="center"> <img src="https://github.com/heibaiying/spring-samples-for-all/blob/master/pictures/ribbon-producer.png"/> </div>
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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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* 这里为了之后直观的看到负载均衡的结果，我们继承了 ApplicationListener,从 WebServerInitializedEvent 获取服务的端口号，并拼接在产品名称上
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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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for (Product product : productList) {
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if (product.getId() == id) {
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return product;
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}
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}
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return null;
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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 {
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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 将服务注册到注册中心
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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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## 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/ribbon-consumer.png"/> </div>
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#### 4.1 导入负载均衡需要的依赖
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```xml
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<!--ribbon 依赖-->
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
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</dependency>
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```
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#### 4.2 指定注册中心的地址
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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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#### 4.3 使用@LoadBalanced配置RestTemplate即可实现客户端负载均衡
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```java
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import org.springframework.cloud.client.loadbalancer.LoadBalanced;
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import org.springframework.context.annotation.Bean;
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import org.springframework.context.annotation.Configuration;
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import org.springframework.web.client.RestTemplate;
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@Configuration
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public class RibbonConfig {
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@LoadBalanced // 配置客户端负载均衡
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@Bean
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public RestTemplate restTemplate() {
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return new RestTemplate();
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}
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}
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```
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#### 4.4 使用RestTemplate调用远程服务
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这里我们在调用远程服务的时候，url填写的是服务名+具体接口地址 ，由于我们的同一个服务会存在多个实例，在使用@LoadBalanced配置RestTemplate调用服务时，客户端就会从按照指定的负载均衡的方式将请求分摊到多个实例上。（默认的负载均衡采用的是RoundRobinRule（轮询）的策略，有特殊需求时候可以采用其他内置的策略规则，或者实现IRule来定义自己的负载均衡策略）。
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```java
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@Service
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public class ProductService implements IProductService {
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@Autowired
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private RestTemplate restTemplate;
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public Product queryProductById(int id) {
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ResponseEntity<Product> responseEntity = restTemplate.getForEntity("http://producer/product/{1}", Product.class, id);
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return responseEntity.getBody();
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}
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public List<Product> queryAllProducts() {
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ResponseEntity<List> responseEntity = restTemplate.getForEntity("http://producer/products", List.class);
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List<Product> productList = responseEntity.getBody();
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return productList;
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}
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public void saveProduct(Product product) {
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restTemplate.postForObject("http://producer/product", product, Void.class);
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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 启动一个Eureka服务、三个producer服务（注意区分端口）、和一个消费者服务
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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 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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## 六、 附1： 关于RestTemplate的说明
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#### 6.1 restTemplate 调用对应resultful接口时候，使用的方法应该与接口声明方式（@GetMapping、@PostMapping、@PutMapping、@DeleteMapping）保持一致。请求类型与对应的调用方法如下。
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- GET请求(getForObject 、getForEntity)
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- POST请求（postForObject 、postForEntity）
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- PUT请求（put）
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- DELETE请求 （delete）
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#### 6.2 ForEntity()和ForObject的区别
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- `ForEntity()`发送一个请求，返回的ResponseEntity包含了响应体所映射成的对象
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- `ForObject()`发送一个请求，返回的请求体将映射为一个对象
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例如：
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```java
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ResponseEntity<Product> responseEntity = restTemplate.getForEntity("http://producer/product/{1}", Product.class, id);
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Product product = restTemplate.getForObject("http://producer/product/{1}", Product.class, id);
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```
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## 七、 附2： 关于ribbon更多负载均衡的策略
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Ribbon内置了多种负载均衡策略，如果有更复杂的需求，可以自己实现IRule。
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#### 7.1 内置的负载均衡的策略如下图
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图片来源于博客：[Ribbon负载均衡策略与自定义配置](https://blog.csdn.net/jrn1012/article/details/77837680)
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#### 7.2 配置文件指定负载均衡的方式
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要设置`IRule`名为的服务名称`users`，您可以设置以下属性：
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```yaml
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users:
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ribbon:
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NFLoadBalancerRuleClassName: com.netflix.loadbalancer.WeightedResponseTimeRule
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```
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#### 7.3 代码指定负载均衡的方式
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```java
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@Configuration
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@RibbonClient(name = "custom", configuration = CustomConfiguration.class)
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public class TestConfiguration {
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}
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```
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```java
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@Configuration
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public class CustomConfiguration {
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@Bean
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public IRule ribbonRule() {
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return new BestAvailableRule();
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}
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}
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```
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在使用代码方式的时候需要注意 [官方文档](http://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-ribbon.html#_customizing_the_ribbon_client)中关于注解方式有以下强调：
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The CustomConfiguration clas must be a @Configuration class, but take care that it is not in a @ComponentScan for the main application context. Otherwise, it is shared by all the @RibbonClients. If you use @ComponentScan (or @SpringBootApplication), you need to take steps to avoid it being included (for instance, you can put it in a separate, non-overlapping package or specify the packages to scan explicitly in the @ComponentScan).
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该`CustomConfiguration`类必须是`@Configuration`标注的，但需要注意的它不是在`@ComponentScan`主应用程序上下文。否则，它将由所有`@RibbonClients`共享。如果你使用`@ComponentScan`（或`@SpringBootApplication`），你需要采取一些措施来避免它被扫描到（例如，你可以把它放在一个独立的，非重叠的包，或用`@ComponentScan`时显示扫描指定的包）。
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