上手spring cloud（二）微应用之间的服务调用

微应用之间的服务调用服务调用示例以商品下单为例，比如将业务拆分为商品服务和订单服务，订单服务会调用商品服务的库存扣减。单个微服务工程，统一按以下目录编排：-product–product-common 商品服务公用对象–product-client 商品服务客户端，以jar包方式被订单服务依赖–product-server 商品服务，要注册到Eureka Server，外部通过product-client来调用我们的微服务工程之间，依赖关系如下：我们从商品微服务工程开始外层product初始pom.xml：<modelVersion>4.0.0</modelVersion><parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.2.RELEASE</version> <relativePath/></parent><groupId>com.hicoview</groupId><artifactId>product</artifactId><version>0.0.1-SNAPSHOT</version><name>product</name><description>Demo project for Spring Boot</description><modules> <module>product-common</module> <module>product-client</module> <module>product-server</module></modules><properties> <java.version>1.8</java.version> <spring-cloud.version>Finchley.RELEASE</spring-cloud.version> <product-common.version>0.0.1-SNAPSHOT</product-common.version></properties><dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>${spring-cloud.version}</version> <type>pom</type> <scope>import</scope> </dependency> <dependency> <groupId>com.hicoview</groupId> <artifactId>product-common</artifactId> <version>${product-common.version}</version> </dependency> </dependencies></dependencyManagement>product-common初始pom.xml：<modelVersion>4.0.0</modelVersion><parent> <groupId>com.hicoview</groupId> <artifactId>product</artifactId> <version>0.0.1-SNAPSHOT</version></parent><artifactId>product-common</artifactId><dependencies> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> </dependency></dependencies>product-client初始pom.xml：<modelVersion>4.0.0</modelVersion><parent> <groupId>com.hicoview</groupId> <artifactId>product</artifactId> <version>0.0.1-SNAPSHOT</version></parent><artifactId>product-client</artifactId><dependencies> <dependency> <groupId>com.hicoview</groupId> <artifactId>product-common</artifactId> </dependency></dependencies>product-server的初始pom.xml：<modelVersion>4.0.0</modelVersion><parent> <groupId>com.hicoview</groupId> <artifactId>product</artifactId> <version>0.0.1-SNAPSHOT</version></parent><artifactId>product-server</artifactId><dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>com.hicoview</groupId> <artifactId>product-common</artifactId> </dependency></dependencies><build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins></build>接下来我们调整product-server工程商品服务需注册到Eureka Server，添加Eureka Client相关依赖：<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-web</artifactId></dependency>启动类加注解@EnableDiscoveryClient：package com.hicoview.product;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;@SpringBootApplication@EnableDiscoveryClientpublic class ProductApplication { public static void main(String[] args) { SpringApplication.run(ProductApplication.class, args); }}配置application.yml：eureka: client: service-url: defaultZone: http://localhost:8761/eureka/spring: application: name: productserver: port: 8080启动product-server，访问注册中心http://localhost:8761，PRODUCT注册上去了，再继续往下看。我们写个简单的服务调用示例一下，订单服务下单逻辑调用商品服务进行扣减库存。继续修改product-server工程package com.hicoview.product.service;import java.util.List;public interface ProductService { // 扣减库存 void decreaseStock();}package com.hicoview.product.service.impl;import com.hicoview.product.service.ProductService;import lombok.extern.slf4j.Slf4j;import org.springframework.stereotype.Service;@Service@Slf4jpublic class ProductServiceImpl implements ProductService { @Override public void decreaseStock() { log.info("——扣减库存—–"); }}spring cloud的RPC服务是使用HTTP方式调用的，所以还要创建ProductController：package com.hicoview.product.controller;import com.hicoview.product.service.ProductService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@RestController@RequestMapping("/product")public class ProductController { @Autowired private ProductService productService; @PostMapping("/decreaseStock") public void decreaseStock() { productService.decreaseStock(); }}接下来修改product-client工程pom.xml增加Feign依赖：<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-openfeign</artifactId></dependency>创建ProductClient：package com.hicoview.product.client;import org.springframework.cloud.openfeign.FeignClient;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.RequestBody;@FeignClient(name=“product”)public interface ProductClient { // 通过Feign来代理对PRODUCT服务的HTTP请求 @PostMapping("/product/decreaseStock") void decreaseStock();}再次启动product-server，没问题的话，把product上传到本地maven仓库：mvn -Dmaven.test.skip=true -U clean install然后初始化订单微服务工程后继续。修改order-server工程order-server的服务可能会被User等其他服务调用，也是个Eureka client，添加依赖：<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-web</artifactId></dependency>启动类加注解@EnableDiscoveryClientpackage com.hicoview.product;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;@SpringBootApplication@EnableDiscoveryClientpublic class ProductApplication { public static void main(String[] args) { SpringApplication.run(ProductApplication.class, args); }}配置application.yml：eureka: client: service-url: defaultZone: http://localhost:8761/eureka/spring: application: name: orderserver: port: 8081启动order-server，访问注册中心http://localhost:8761/：ORDER服务注册成功后，继续调整order-server工程由于订单服务要调用商品服务，需添加对product-client依。修改pom.xml：<dependency> <groupId>com.hicoview</groupId> <artifactId>product-client</artifactId></dependency>对版本的管理统一交给上层，修改上层order的pom.xml，增加以下配置：<properties> … <product-client.version>0.0.1-SNAPSHOT</product-client.version></properties><dependencyManagement> <dependencies> … <dependency> <groupId>com.hicoview</groupId> <artifactId>product-client</artifactId> <version>${product-client.version}</version> </dependency> </dependencies></dependencyManagement>回到order-server，修改启动类，添加Feign扫描路径：package com.hicoview.order;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.cloud.openfeign.EnableFeignClients;@SpringBootApplication@EnableDiscoveryClient@EnableFeignClients(basePackages = “com.hicoview.product.client”)public class OrderApplication { public static void main(String[] args) { SpringApplication.run(OrderApplication.class, args); }}然后按顺序创建Controller、Service：package com.hicoview.order.controller;import com.hicoview.order.service.OrderService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@RestController@RequestMapping("/order")public class OrderController { @Autowired private OrderService orderService; // 创建订单 @PostMapping("/create") public void create() { orderService.createOrder(); }}public interface OrderService { void createOrder();}@Service@Slf4jpublic class OrderServiceImpl implements OrderService { @Autowired private ProductClient productClient; @Override public void createOrder() { log.info("——创建订单—–"); // 调用商品扣减服务 productClient.decreaseStock(); }}启动order-server，发起下单请求：curl -X POST http://localhost:8081/order/create服务调用成功，order-server和product-server输出：2019-02-26 11:09:58.408 INFO 3021 — [nio-8081-exec-3] c.h.order.service.impl.OrderServiceImpl : ——创建订单—–2019-02-26 11:09:58.430 INFO 3015 — [nio-8080-exec-3] c.h.p.service.impl.ProductServiceImpl : ——扣减库存—–为了示例的极简，上面服务调用没有涉及到入参和返回值。如果需要定义参数或返回值，考虑到内外部都会用到，需将参数bean定义在product-common中作为公共bean。Feign和RestTemplateRest服务的调用，可以使用Feign或RestTemplate来完成，上面示例我们使用了Feign。Feign（推荐）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。Feign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。RestTemplateRestTemplate提供了多种便捷访问远程Http服务的方法，可以了解下。第一种方式，直接使用RestTemplate，URL写死：// 1. RestTemplate restTemplate = new RestTemplate();restTemplate.getForObject(“http://localhost:8080/product/decreaseStock”, String.class);这种方式直接使用目标的IP，而线上部署的IP地址可能会切换，同一个服务还会启多个进程，所以有弊端。第二种方式，利用LoadBalancerClient，通过应用名获取URL，然后再使用RestTemplate：@Autowiredprivate LoadBalancerClient loadBalancerClient;// 1. 第二种方式，通过应用名字拿到其中任意一个host和portServiceInstance serviceInstance = loadBalancerClient.choose(“PRODUCT”);String url = String.format(“http://%s:%s”, serviceInstance.getHost(), serviceInstance.getPort() + “/product/decreaseStock”);RestTemplate restTemplate = new RestTemplate();restTemplate.getForObject(url, String.class);第三种方式，写一个config把RestTemplate作为一个bean配置上去：@Componentpublic class RestTemplateConfig { @Bean @LoadBalanced public RestTemplate restTemplate() { return new RestTemplate(); }}@Autowiredprivate RestTemplate restTemplate;// 使用时url里直接用应用名PRODUCT即可restTemplate.getForObject(“http://PRODUCT/product/decreaseStock”, String.class);Ribbon客户端负载均衡器Spring Cloud Ribbon是一个基于HTTP和TCP的客户端负载均衡工具，它基于Netflix Ribbon实现。通过Spring Cloud的封装，可以让我们轻松地将面向服务的REST模版请求自动转换成客户端负载均衡的服务调用。Spring Cloud Ribbon虽然只是一个工具类框架，它不像服务注册中心、配置中心、API网关那样需要独立部署，但是它几乎存在于每一个Spring Cloud构建的微服务和基础设施中。在Spring Cloud中，Ribbon可自动从Eureka Server获取服务提供者地址列表，并基于负载均衡算法，请求其中一个服务提供者实例。还有微服务之间的调用，通过Feign或RestTemplate找到一个目标服务。以及API网关Zuul的请求转发等内容，实际上都是通过Ribbon来实现的。