Spring-Cloud-Gateway源码分析系列| Spring-Cloud-Gateway初始化

转自：https://blog.csdn.net/qq_43253123/article/details/83311393

Spring-Cloud项目使用EnableAutoConfiguration注解自动
初始化配置信息，Spring-Cloud-Gateway同样，Spring-Cloud-Gateway下的spring.factories（在包spring-cloud-gateway-core）。

如下:

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
//依赖包的校验配置
org.springframework.cloud.gateway.config.GatewayClassPathWarningAutoConfiguration,\
//网关的核心配置
org.springframework.cloud.gateway.config.GatewayAutoConfiguration,\
//负载均衡相关依赖配置信息
org.springframework.cloud.gateway.config.GatewayLoadBalancerClientAutoConfiguration,\
//流控的依赖配置信息
org.springframework.cloud.gateway.config.GatewayRedisAutoConfiguration,\
//注册中心相关的依赖配置
org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration

配置功能：
分析配置功能前先了解下springboot常用的注解的含义：

执行顺序
@AutoConfigureAfter：在指定的配置类初始化后再加载
@AutoConfigureBefore：在指定的配置类初始化前加载
@AutoConfigureOrder：数越小越先初始化

条件配置
@ConditionalOnClass ： classpath中存在该类时起效
@ConditionalOnMissingClass ： classpath中不存在该类时起效
@ConditionalOnBean ： DI容器中存在该类型Bean时起效
@ConditionalOnMissingBean ： DI容器中不存在该类型Bean时起效
@ConditionalOnSingleCandidate ： DI容器中该类型Bean只有一个或@Primary的只有一个时起效
@ConditionalOnExpression ： SpEL表达式结果为true时
@ConditionalOnProperty ： 参数设置或者值一致时起效
@ConditionalOnResource ： 指定的文件存在时起效
@ConditionalOnJndi ： 指定的JNDI存在时起效
@ConditionalOnJava ： 指定的Java版本存在时起效
@ConditionalOnWebApplication ： Web应用环境下起效
@ConditionalOnNotWebApplication ： 非Web应用环境下起效

1.GatewayClassPathWarningAutoConfiguration配置
GatewayClassPathWarningAutoConfiguration配置用于检查项目是否正确导入 spring-boot-starter-webflux 依赖，而不是错误导入 spring-boot-starter-web 依赖，同时 GatewayClassPathWarningAutoConfiguration配置在EnableAutoConfiguration配置加载前加载。
接下来我看代码如何实现：

@Configuration
//执行顺序注解
//当前注解标识需要在GatewayAutoConfiguration前加载此配置
@AutoConfigureBefore(GatewayAutoConfiguration.class)
public class GatewayClassPathWarningAutoConfiguration {
    @Configuration
    //条件判断注解
    //classpath中存在org.springframework.web.servlet.DispatcherServlet时起效，标识项目导入了spring-boot-starter-web包
    @ConditionalOnClass(name = "org.springframework.web.servlet.DispatcherServlet")
    protected static class SpringMvcFoundOnClasspathConfiguration {

        public SpringMvcFoundOnClasspathConfiguration() {
           //当前项目导入了spring-boot-starter-web依赖时，打印警告日志
            log.warn(BORDER+"Spring MVC found on classpath, which is incompatible with Spring Cloud Gateway at this time. "+
                    "Please remove spring-boot-starter-web dependency."+BORDER);
        }

    }
    @Configuration
    //条件判断注解
    //classpath中不存在org.springframework.web.reactive.DispatcherHandler时起效，标识项目未导入了spring-boot-starter-webflux包
    @ConditionalOnMissingClass("org.springframework.web.reactive.DispatcherHandler")
    protected static class WebfluxMissingFromClasspathConfiguration {
        public WebfluxMissingFromClasspathConfiguration() {
      //当前项目未导入了boot-starter-webflux依赖时，打印警告日志
            log.warn(BORDER+"Spring Webflux is missing from the classpath, which is required for Spring Cloud Gateway at this time. "+
                    "Please add spring-boot-starter-webflux dependency."+BORDER);
        }

    }
}

2.GatewayLoadBalancerClientAutoConfiguration

GatewayLoadBalancerClientAutoConfiguration配置作用是初始化 LoadBalancerClientFilter 路由的负载均衡拦截器。

@Configuration
//条件判断注解
//classpath中存在LoadBalancerClient和RibbonAutoConfiguration和DispatcherHandler时此配置起效
@ConditionalOnClass({LoadBalancerClient.class, RibbonAutoConfiguration.class, DispatcherHandler.class})
//执行顺序注解
@AutoConfigureAfter(RibbonAutoConfiguration.class)
public class GatewayLoadBalancerClientAutoConfiguration {
    // GlobalFilter beans
    @Bean
    //条件判断注解
    //DI容器中存在LoadBalancerClient类型Bean时起效
    @ConditionalOnBean(LoadBalancerClient.class)
    public LoadBalancerClientFilter loadBalancerClientFilter(LoadBalancerClient client) {
        return new LoadBalancerClientFilter(client);
    }
}

3.GatewayRedisAutoConfiguration
GatewayRedisAutoConfiguration 配置作用是初始化初始化 RedisRateLimiter 限流功能的。RequestRateLimiterGatewayFilterFactory 基于 RedisRateLimiter 实现网关的限流功能，代码略。

4.GatewayAutoConfiguration
GatewayAutoConfiguration配置是Spring Cloud Gateway 核心配置类，初始化如下：

• NettyConfiguration 底层通信netty配置
• GlobalFilter （AdaptCachedBodyGlobalFilter，RouteToRequestUrlFilter，ForwardRoutingFilter，ForwardPathFilter，
• WebsocketRoutingFilter，WeightCalculatorWebFilter等）
• FilteringWebHandler
• GatewayProperties
• PrefixPathGatewayFilterFactory
• RoutePredicateFactory
• RouteDefinitionLocator
• RouteLocator
• RoutePredicateHandlerMapping 查找匹配到 Route并进行处理
• GatewayWebfluxEndpoint 管理网关的 HTTP API

@Configuration
//条件注解
//通过 spring.cloud.gateway.enabled配置网关的开启与关闭
//matchIfMissing = true => 网关默认开启。
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@EnableConfigurationProperties
@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)
@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})
@ConditionalOnClass(DispatcherHandler.class)
public class GatewayAutoConfiguration {
    @Configuration
    //当classpath中存在HttpClient起效
    @ConditionalOnClass(HttpClient.class)
    protected static class NettyConfiguration {
        .....略
    }
    
    //加载配置beans
    // ConfigurationProperty beans
    @Bean
    public GatewayProperties gatewayProperties() {
        return new GatewayProperties();
    }
    @Bean
    public SecureHeadersProperties secureHeadersProperties() {
        return new SecureHeadersProperties();
    }
    
    // GlobalFilter beans
    //加载全局的拦截器
    @Bean
    public AdaptCachedBodyGlobalFilter adaptCachedBodyGlobalFilter() {
        return new AdaptCachedBodyGlobalFilter();
    }

    @Bean
    public RouteToRequestUrlFilter routeToRequestUrlFilter() {
        return new RouteToRequestUrlFilter();
    }

    @Bean
    @ConditionalOnBean(DispatcherHandler.class)
    public ForwardRoutingFilter forwardRoutingFilter(DispatcherHandler dispatcherHandler) {
        return new ForwardRoutingFilter(dispatcherHandler);
    }

    @Bean
    public ForwardPathFilter forwardPathFilter() {
        return new ForwardPathFilter();
    }

    @Bean
    public WebSocketService webSocketService() {
        return new HandshakeWebSocketService();
    }
    @Bean
    public WebsocketRoutingFilter websocketRoutingFilter(WebSocketClient webSocketClient,
        return new WebsocketRoutingFilter(webSocketClient, webSocketService, headersFilters);
    }
    @Bean
    public WeightCalculatorWebFilter weightCalculatorWebFilter(Validator validator) {
        return new WeightCalculatorWebFilter(validator);
    }
}

5.GatewayDiscoveryClientAutoConfiguration

GatewayDiscoveryClientAutoConfiguration配置的作用是初始化配置路由中的注册发现服务信息。

@Configuration
//同4
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@AutoConfigureBefore(GatewayAutoConfiguration.class)
@ConditionalOnClass({DispatcherHandler.class, DiscoveryClient.class})
@EnableConfigurationProperties
public class GatewayDiscoveryClientAutoConfiguration {

    @Bean
    //当classpath中存在DiscoveryClient起效
    @ConditionalOnBean(DiscoveryClient.class)
    //通过spring.cloud.gateway.discovery.locator.enabled配置注册中心查找的开启与关闭
    @ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
    public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
            DiscoveryClient discoveryClient, DiscoveryLocatorProperties properties) {
        return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
    }
}

通过自动加载初始化上述五个配置实例Spring-Cloud-Gateway就完成自身的信息加载和初始化工作。