一、序言

我们都知道Spring Cloud Gateway是一个基于Spring Boot、Spring WebFlux、Project Reactor构建的高性能网关，旨在提供简单、高效的API路由。

Spring Cloud Gateway基于Netty运行，因此在传统Servlet容器中或者打成war包是不能正常运行的。

二、代码示例

这里我们注册中心选型的是Nacos，如果还没有安装Nacos，请参考：Nacos快速安装部署。

1、父工程spring-cloud-gateway-learning

	<modules>
	        <module>spring-cloud-api-gateway</module>
	        <module>spring-cloud-user-service</module>
	        <module>spring-cloud-message-service</module>
	</modules>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring.boot.version>2.3.7.RELEASE</spring.boot.version>
        <spring.cloud.version>Hoxton.SR12</spring.cloud.version>
        <spring.cloud.alibaba.version>2.2.6.RELEASE</spring.cloud.alibaba.version>
        <commons.lang3.version>3.12.0</commons.lang3.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>${commons.lang3.version}</version>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-parent</artifactId>
                <version>${spring.boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring.cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring.cloud.alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

备注：具体Spring Cloud各版本说明请参考Spring Cloud Alibaba版本说明。

2、子工程spring-cloud-api-gateway

(1) pom.xml

<parent>
        <groupId>com.universe</groupId>
        <artifactId>spring-cloud-gateway-learning</artifactId>
        <version>1.0-SNAPSHOT</version>
</parent>

<dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-gateway</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
</dependencies>

(2) 配置文件和代码示例

1. bootstrap.yml

spring:
  application:
    name: api-gateway
server:
  port: 9000

2. application.yml

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service
          predicates:
            - Path=/user/**
        - id: message-service
          uri: lb://message-service
          predicates:
            - Path=/message/**
    nacos:
      discovery:
        server-addr: localhost:8848

如果URI以lb开头，比如如上配置中的lb://user-service，Spring Cloud Gateway会用ReactiveLoadBalancerClientFilter 解析服务名为user-service的实例对应的实际host和端口，并做集群负载均衡。

这项功能通过全局过滤器ReactiveLoadBalancerClientFilter 实现，官网描述如下：

3. RouteRecordGlobalFilter

@Slf4j
@Component
public class RouteRecordGlobalFilter implements GlobalFilter, Ordered {

	@Override
	public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
		// RouteToRequestUrlFilter会把实际路由的URL通过该属性保存
		URI proxyRequestUri = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR);
		long start = System.currentTimeMillis();

		return chain.filter(exchange).then(Mono.fromRunnable(() -> {
			long end = System.currentTimeMillis();
			log.info("实际调用地址为：{}，调用耗时为：{}ms", proxyRequestUri, (end - start));
		}));
	}

	@Override
	public int getOrder() {
		// 优先级设为最低，先让RouteToRequestUrlFilter先调用
		return Ordered.LOWEST_PRECEDENCE;
	}
}

RouteRecordGlobalFilter 这个全局过滤器我们主要用来记录路由后的实际代理地址，以及调用耗时。

我们看下RouteToRequestUrlFilter的描述会发现实际路由地址会通过ServerWebExchange中名为ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR的属性保存。

关于RouteToRequestUrlFilter的部分源码如下：

@Override
	public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
		Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);
		if (route == null) {
			return chain.filter(exchange);
		}
		log.trace("RouteToRequestUrlFilter start");
		URI uri = exchange.getRequest().getURI();
		boolean encoded = containsEncodedParts(uri);
		URI routeUri = route.getUri();

		if (hasAnotherScheme(routeUri)) {
			// this is a special url, save scheme to special attribute
			// replace routeUri with schemeSpecificPart
			exchange.getAttributes().put(GATEWAY_SCHEME_PREFIX_ATTR,
					routeUri.getScheme());
			routeUri = URI.create(routeUri.getSchemeSpecificPart());
		}

		if ("lb".equalsIgnoreCase(routeUri.getScheme()) && routeUri.getHost() == null) {
			// Load balanced URIs should always have a host. If the host is null it is
			// most
			// likely because the host name was invalid (for example included an
			// underscore)
			throw new IllegalStateException("Invalid host: " + routeUri.toString());
		}

		URI mergedUrl = UriComponentsBuilder.fromUri(uri)
				// .uri(routeUri)
				.scheme(routeUri.getScheme()).host(routeUri.getHost())
				.port(routeUri.getPort()).build(encoded).toUri();
		exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, mergedUrl);
		return chain.filter(exchange);
	}

备注：更多关于全局过滤器的介绍请参考 Spring Cloud Gateway全局过滤器。

3、子工程spring-cloud-user-service

(1) pom.xml

<parent>
        <groupId>com.universe</groupId>
        <artifactId>spring-cloud-gateway-learning</artifactId>
        <version>1.0-SNAPSHOT</version>
</parent>

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
</dependencies>

(2) 配置文件

1. bootstrap.yml

spring:
  application:
    name: user-service
server:
  servlet:
    context-path: /user

---
spring:
  profiles: user-service-master
server:
  port: 9091

---
spring:
  profiles: user-service-slave
server:
  port: 9092

2. application.yml

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848

3. UserController

@RestController
public class UserController {

	@GetMapping("/info")
	public Map<String, Object> getUserInfo() {
	Random random = new Random();
		int waitTime = random.nextInt(1000);
		LockSupport.parkNanos(1000 * 1000 * waitTime);
		
		Map<String, Object> result = new HashMap<>();
		result.put("name", "Nick");
		result.put("age", 25);
		return result;
	}
}

4、子工程spring-cloud-message-service

(1) pom.xml

<parent>
        <groupId>com.universe</groupId>
        <artifactId>spring-cloud-gateway-learning</artifactId>
        <version>1.0-SNAPSHOT</version>
</parent>

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
</dependencies>

(2) 配置文件和代码示例

1. bootstrap.yml

spring:
  application:
    name: message-service
server:
  servlet:
    context-path: /message

---
spring:
  profiles: message-service-master
server:
  port: 9093

---
spring:
  profiles: message-service-slave
server:
  port: 9094

2. application.yml

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848

3. MessageController

@RestController
public class MessageController {

	@GetMapping("/info")
	public Map<String, Object> getMessageInfo() {
	Random random = new Random();
		int waitTime = random.nextInt(1000);
		LockSupport.parkNanos(1000 * 1000 * waitTime);
	
		Map<String, Object> result = new HashMap<>();
		result.put("id", 1);
		result.put("title", "我爱中国");
		return result;
	}
}

三、测试结果

分别启动api-gateway、指定概要文件启动两个user-service服务实例、和两个message-service服务实例，查看Nacos控制台。

可以看到，api-gateway启动了一个服务实例，user-service和message-service都启动了两个服务实例。

备注：IDEA运行时指定Active Profiles即可。

1、集群负载均衡测试

连续访问http://localhost:9000/user/info，可以看到user-service集群服务实例被轮询调用。

2、服务路由测试

分别访问 http://localhost:9000/user/info、http://localhost:9000/message/info，我们可以看到基于路径匹配的服务路由分发是成功的。