Zuul 处理流程

一、spring-cloud-starter-zuul starter

1.我们先查看spring-cloud-starter-zuul starter包下有什么，这里的重点就是pom.xml文件，ZuulDeprecationWarningAutoConfiguration.java

2.打开org.springframework.cloud/spring-cloud-starter-zuul/pom.xml ，可以看到是依赖了spring-cloud-starter-netflix-zuul

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-netflix</artifactId>
  <version>2.2.5.RELEASE</version>
  <relativePath>..</relativePath> <!-- lookup parent from repository -->
 </parent>
 <artifactId>spring-cloud-starter-zuul</artifactId>
 <name>spring-cloud-starter-zuul</name>
 <description>Spring Cloud Starter Zuul (deprecated, please use spring-cloud-starter-netflix-zuul)</description>
 <url>https://projects.spring.io/spring-cloud</url>
 <organization>
  <name>Pivotal Software, Inc.</name>
  <url>https://www.spring.io</url>
 </organization>
 <properties>
  <main.basedir>${basedir}/../..</main.basedir>
 </properties>
 <dependencies>
  <dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
  </dependency>
 </dependencies>
</project>

1.我们查看spring-cloud-starter-netflix-zuul包

2.打开pom.xml可以看到依赖了com.netflix.zuul，所以说Spring Cloud Zuul是基于netflix公司的zuul实现的，除此之外还添加了hystrix及ribbon依赖，所以zuul是自带这两个功能的，spring-boot-starter-web依赖可以使应用成为web应用，spring-boot-starter-actuator是监控依赖

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix</artifactId>
        <version>2.2.5.RELEASE</version>
    </parent>
    <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
    <name>Spring Cloud Starter Netflix Zuul</name>
    <description>Spring Cloud Starter Netflix Zuul</description>
    <url>https://projects.spring.io/spring-cloud</url>
    <organization>
        <name>Pivotal Software, Inc.</name>
        <url>https://www.spring.io</url>
    </organization>
    <properties>
        <main.basedir>${basedir}/../../..</main.basedir>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-archaius</artifactId>
        </dependency>
        <dependency>
            <groupId>com.netflix.zuul</groupId>
            <artifactId>zuul-core</artifactId>
        </dependency>
    </dependencies>
</project>

1./META-INF/spring.provides 依赖spring-platform-netflix-core模块及zuul-core模块
1 provides: spring-platform-netflix-core, zuul-core

2.现在我们进入spring-platform-netflix-core，看看Spring是怎样集成Netflix的一系列框架了，下面是代码框架图

3.可以看到这个JAR包也包含了spring.factories文件，所以SpringBoot项目启动的时候会检索此配置文件，此文件是zuul实现自动注册配置的关键，下面可以看到熟悉的zuul,hystrix,feign,ribbon的自动配置类

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.archaius.ArchaiusAutoConfiguration,\
org.springframework.cloud.netflix.feign.ribbon.FeignRibbonClientAutoConfiguration,\
org.springframework.cloud.netflix.feign.FeignAutoConfiguration,\
org.springframework.cloud.netflix.feign.encoding.FeignAcceptGzipEncodingAutoConfiguration,\
org.springframework.cloud.netflix.feign.encoding.FeignContentGzipEncodingAutoConfiguration,\
org.springframework.cloud.netflix.hystrix.HystrixAutoConfiguration,\
org.springframework.cloud.netflix.hystrix.security.HystrixSecurityAutoConfiguration,\
org.springframework.cloud.netflix.ribbon.RibbonAutoConfiguration,\
org.springframework.cloud.netflix.rx.RxJavaAutoConfiguration,\
org.springframework.cloud.netflix.metrics.servo.ServoMetricsAutoConfiguration,\
org.springframework.cloud.netflix.zuul.ZuulServerAutoConfiguration,\
org.springframework.cloud.netflix.zuul.ZuulProxyAutoConfiguration

org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.cloud.netflix.metrics.ServoEnvironmentPostProcessor

1.我们现在关心Zuul的自动配置类，从上面spring.factories文件可以看到和Zuul相关的是自动配置了两个类，下图可以看到这两个有继承关系，ZuulProxyAutoConfiguration功能最为完全

2.ZuulServerAutoConfiguration 与 ZuulProxyAutoConfiguration

3.ZuulServerAutoConfiguration自动配置类，启动类上如果有

@EnableZuulServer则此类生效
1.下面代码可以看到大量使用了@Conditional作为条件判断，注意这个ZuulController这个Bean，它是Zuul的请求入口，这个类实现了Controller了，说明这里也使用了Spring MVC DispatcherServlet，
2.同时此类注册了大量的ZuulFilter
代码:

/**
 * @author
 */
@Configuration // 声明是配置类
@EnableConfigurationProperties({ ZuulProperties.class }) // 激活 zuul配置
@ConditionalOnClass(ZuulServlet.class) // 条件1 存在ZuulServlet.class
@ConditionalOnBean(ZuulServerMarkerConfiguration.Marker.class) // 条件2 存在ZuulServerMarkerConfiguration.Marker.class bean, 即应用使用@EnableZuulServer注解
// Make sure to get the ServerProperties from the same place as a normal web app would
@Import(ServerPropertiesAutoConfiguration.class) // 配置ServerProperties实例
public class ZuulServerAutoConfiguration {

    @Autowired
    protected ZuulProperties zuulProperties;

    @Autowired
    protected ServerProperties server;

    @Autowired(required = false)
    private ErrorController errorController;

    @Bean
    public HasFeatures zuulFeature() {
        return HasFeatures.namedFeature("Zuul (Simple)", ZuulServerAutoConfiguration.class);
    }

    @Bean
    @Primary
    public CompositeRouteLocator primaryRouteLocator(
            Collection<RouteLocator> routeLocators) {
        return new CompositeRouteLocator(routeLocators);
    }

    @Bean
    @ConditionalOnMissingBean(SimpleRouteLocator.class)
    public SimpleRouteLocator simpleRouteLocator() {
        return new SimpleRouteLocator(this.server.getServletPrefix(),
                this.zuulProperties);
    }

    /**
 * zuulController, 包装了一个ZuulServlet类型的servlet, 实现对ZuulServlet类型的servlet的初始化.
 *
 * @return
 */
    @Bean
    public ZuulController zuulController() {
        return new ZuulController();
    }

    @Bean
    public ZuulHandlerMapping zuulHandlerMapping(RouteLocator routes) {
        ZuulHandlerMapping mapping = new ZuulHandlerMapping(routes, zuulController());
        mapping.setErrorController(this.errorController);
        return mapping;
    }

    @Bean
    public ApplicationListener<ApplicationEvent> zuulRefreshRoutesListener() {
        return new ZuulRefreshListener();
    }

    @Bean
    @ConditionalOnMissingBean(name = "zuulServlet")
    public ServletRegistrationBean zuulServlet() {
        ServletRegistrationBean servlet = new ServletRegistrationBean(new ZuulServlet(),
                this.zuulProperties.getServletPattern());
        // The whole point of exposing this servlet is to provide a route that doesn't
        // buffer requests.
        servlet.addInitParameter("buffer-requests", "false");
        return servlet;
    }

    // pre filters

    @Bean
    public ServletDetectionFilter servletDetectionFilter() {
        return new ServletDetectionFilter();
    }

    @Bean
    public FormBodyWrapperFilter formBodyWrapperFilter() {
        return new FormBodyWrapperFilter();
    }

    @Bean
    public DebugFilter debugFilter() {
        return new DebugFilter();
    }

    @Bean
    public Servlet30WrapperFilter servlet30WrapperFilter() {
        return new Servlet30WrapperFilter();
    }

    // post filters

    @Bean
    public SendResponseFilter sendResponseFilter() {
        return new SendResponseFilter();
    }

    @Bean
    public SendErrorFilter sendErrorFilter() {
        return new SendErrorFilter();
    }

    @Bean
    public SendForwardFilter sendForwardFilter() {
        return new SendForwardFilter();
    }

    @Bean
    @ConditionalOnProperty(value = "zuul.ribbon.eager-load.enabled", matchIfMissing = false)
    public ZuulRouteApplicationContextInitializer zuulRoutesApplicationContextInitiazer(
            SpringClientFactory springClientFactory) {
        return new ZuulRouteApplicationContextInitializer(springClientFactory,
                zuulProperties);
    }

    @Configuration
    protected static class ZuulFilterConfiguration {

        @Autowired
        private Map<String, ZuulFilter> filters;

        @Bean
        public ZuulFilterInitializer zuulFilterInitializer(
                CounterFactory counterFactory, TracerFactory tracerFactory) {
            FilterLoader filterLoader = FilterLoader.getInstance();
            FilterRegistry filterRegistry = FilterRegistry.instance();
            return new ZuulFilterInitializer(this.filters, counterFactory, tracerFactory, filterLoader, filterRegistry);
        }

    }

    @Configuration
    @ConditionalOnClass(CounterService.class)
    protected static class ZuulCounterFactoryConfiguration {

        @Bean
        @ConditionalOnBean(CounterService.class)
        public CounterFactory counterFactory(CounterService counterService) {
            return new DefaultCounterFactory(counterService);
        }
    }

    @Configuration
    protected static class ZuulMetricsConfiguration {

        @Bean
        @ConditionalOnMissingBean(CounterFactory.class)
        public CounterFactory counterFactory() {
            return new EmptyCounterFactory();
        }

        @ConditionalOnMissingBean(TracerFactory.class)
        @Bean
        public TracerFactory tracerFactory() {
            return new EmptyTracerFactory();
        }

    }

    private static class ZuulRefreshListener
            implements ApplicationListener<ApplicationEvent> {

        @Autowired
        private ZuulHandlerMapping zuulHandlerMapping;

        private HeartbeatMonitor heartbeatMonitor = new HeartbeatMonitor();

        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            if (event instanceof ContextRefreshedEvent
                    || event instanceof RefreshScopeRefreshedEvent
                    || event instanceof RoutesRefreshedEvent) {
                this.zuulHandlerMapping.setDirty(true);
            }
            else if (event instanceof HeartbeatEvent) {
                if (this.heartbeatMonitor.update(((HeartbeatEvent) event).getValue())) {
                    this.zuulHandlerMapping.setDirty(true);
                }
            }
        }

    }

}

1.ZuulProxyAutoConfiguration自动配置类，启动类上如果有对应@EnableZuulProxy则此类生效

2.由上面此类的继承图可以发现这个类继承了ZuulServerAutoConfiguration，所以此类拥有ZuulServerAutoConfiguration的所有功能，并在此基础上添加了使用了服务发现作为路由寻址功能

代码：

/**
 * @author
 */
@Configuration // 声明是配置类
@Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class, // 引入RibbonCommandFactory配置
        RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,
        RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class,
        HttpClientConfiguration.class })
@ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class) // 条件2 存在ZuulProxyMarkerConfiguration.Marker.class bean, 即应用使用@EnableZuulProxy注解
public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration {

    @SuppressWarnings("rawtypes")
    @Autowired(required = false)
    private List<RibbonRequestCustomizer> requestCustomizers = Collections.emptyList();

    /**
 * 网关服务注册实例信息
 */
    @Autowired(required = false)
    private Registration registration;

    /**
 * 服务发现客户端
 */
    @Autowired
    private DiscoveryClient discovery;

    /**
 * serviceId和路由的映射逻辑
 */
    @Autowired
    private ServiceRouteMapper serviceRouteMapper;

    @Override
    public HasFeatures zuulFeature() {
        return HasFeatures.namedFeature("Zuul (Discovery)",
                ZuulProxyAutoConfiguration.class);
    }

    /**
 * 静态和动态路由寻址: 静态从配置文件获取, 动态通过服务发现客户端完成. 后者优先级更高
 * @return
 */
    @Bean
    @ConditionalOnMissingBean(DiscoveryClientRouteLocator.class)
    public DiscoveryClientRouteLocator discoveryRouteLocator() {
        return new DiscoveryClientRouteLocator(this.server.getServletPrefix(),
                this.discovery, this.zuulProperties, this.serviceRouteMapper, this.registration);
    }

    // pre filters
    @Bean
    public PreDecorationFilter preDecorationFilter(RouteLocator routeLocator,
            ProxyRequestHelper proxyRequestHelper) {
        return new PreDecorationFilter(routeLocator, this.server.getServletPrefix(),
                this.zuulProperties, proxyRequestHelper);
    }

    // route filters
    @Bean
    public RibbonRoutingFilter ribbonRoutingFilter(ProxyRequestHelper helper,
            RibbonCommandFactory<?> ribbonCommandFactory) {
        RibbonRoutingFilter filter = new RibbonRoutingFilter(helper, ribbonCommandFactory,
                this.requestCustomizers);
        return filter;
    }

    @Bean
    @ConditionalOnMissingBean({SimpleHostRoutingFilter.class, CloseableHttpClient.class})
    public SimpleHostRoutingFilter simpleHostRoutingFilter(ProxyRequestHelper helper,
            ZuulProperties zuulProperties,
            ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
            ApacheHttpClientFactory httpClientFactory) {
        return new SimpleHostRoutingFilter(helper, zuulProperties,
                connectionManagerFactory, httpClientFactory);
    }

    @Bean
    @ConditionalOnMissingBean({SimpleHostRoutingFilter.class})
    public SimpleHostRoutingFilter simpleHostRoutingFilter2(ProxyRequestHelper helper,
                                                           ZuulProperties zuulProperties,
                                                           CloseableHttpClient httpClient) {
        return new SimpleHostRoutingFilter(helper, zuulProperties,
                httpClient);
    }

    @Bean
    public ApplicationListener<ApplicationEvent> zuulDiscoveryRefreshRoutesListener() {
        return new ZuulDiscoveryRefreshListener();
    }

    @Bean
    @ConditionalOnMissingBean(ServiceRouteMapper.class)
    public ServiceRouteMapper serviceRouteMapper() {
        return new SimpleServiceRouteMapper();
    }

    @Configuration
    @ConditionalOnMissingClass("org.springframework.boot.actuate.endpoint.Endpoint")
    protected static class NoActuatorConfiguration {

        @Bean
        public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {
            ProxyRequestHelper helper = new ProxyRequestHelper();
            helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());
            helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());
            return helper;
        }

    }

    /**
 * 添加 Endpoint
 */
    @Configuration
    @ConditionalOnClass(Endpoint.class)
    protected static class EndpointConfiguration {

        @Autowired(required = false)
        private TraceRepository traces;

        @ConditionalOnEnabledEndpoint("routes")
        @Bean
        public RoutesEndpoint routesEndpoint(RouteLocator routeLocator) {
            return new RoutesEndpoint(routeLocator);
        }

        @ConditionalOnEnabledEndpoint("routes")
        @Bean
        public RoutesMvcEndpoint routesMvcEndpoint(RouteLocator routeLocator,
                RoutesEndpoint endpoint) {
            return new RoutesMvcEndpoint(endpoint, routeLocator);
        }

        @ConditionalOnEnabledEndpoint("filters")
        @Bean
        public FiltersEndpoint filtersEndpoint() {
            FilterRegistry filterRegistry = FilterRegistry.instance();
            return new FiltersEndpoint(filterRegistry);
        }

        @Bean
        public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {
            TraceProxyRequestHelper helper = new TraceProxyRequestHelper();
            if (this.traces != null) {
                helper.setTraces(this.traces);
            }
            helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());
            helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());
            return helper;
        }
    }

    private static class ZuulDiscoveryRefreshListener
            implements ApplicationListener<ApplicationEvent> {

        private HeartbeatMonitor monitor = new HeartbeatMonitor();

        @Autowired
        private ZuulHandlerMapping zuulHandlerMapping;

        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            if (event instanceof InstanceRegisteredEvent) {
                reset();
            }
            else if (event instanceof ParentHeartbeatEvent) {
                ParentHeartbeatEvent e = (ParentHeartbeatEvent) event;
                resetIfNeeded(e.getValue());
            }
            else if (event instanceof HeartbeatEvent) {
                HeartbeatEvent e = (HeartbeatEvent) event;
                resetIfNeeded(e.getValue());
            }

        }

        private void resetIfNeeded(Object value) {
            if (this.monitor.update(value)) {
                reset();
            }
        }

        private void reset() {
            this.zuulHandlerMapping.setDirty(true);
        }

    }

}

1.ZuulServerAutoConfiguration 与 ZuulProxyAutoConfiguration具体使用哪种模式，是分别通过@EnableZuulServer 和@EnableZuulProxy注解来区别的

2.前者使用了ZuulProperties进行配置路由寻址;

3.后者在原来的基础上添加了使用了服务发现作为路由寻址功能, 并使用Ribbon做客户端的负载均衡，这个最为常用;

二、@EnableZuulProxy

@EnableZuulProxy注解

/**
 * Sets up a Zuul server endpoint and installs some reverse proxy filters in it, so it can
 * forward requests to backend servers. The backends can be registered manually through
 * configuration or via DiscoveryClient.
 *
 * @see EnableZuulServer for how to get a Zuul server without any proxying
 *
 * @author
 */
@EnableCircuitBreaker
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(ZuulProxyMarkerConfiguration.class)
public @interface EnableZuulProxy {
}

@EnableZuulProxy分析

@EnableCircuitBreaker注解用于开启短路器功能

/**
 * Annotation to enable a CircuitBreaker implementation.
 * http://martinfowler.com/bliki/CircuitBreaker.html
 * @author
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {

}

@Import(ZuulProxyMarkerConfiguration.class)

ZuulProxyMarkerConfiguration.Marker.class

@Configuration
public class ZuulProxyMarkerConfiguration {
    @Bean
    public Marker zuulProxyMarkerBean() {
        return new Marker();
    }

    class Marker {
    }
}

三、使用Consul作为注册中心

@EnableZuulProxy模式下的zuul需要注册中心的支持，因为eureka已经被抛弃了，我这里选用的是Consul

1.添加Maven依赖

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-consul-discovery</artifactId>
</dependency>

2.启动类上加上@EnableDiscoveryClient注解

@EnableZuulProxy
@EnableDiscoveryClient
@SpringBootApplication
public class ZuulApplication {

    public static void main(String[] args) {
        SpringApplication.run(ZuulApplication.class, args);
    }

}

3.通过以上所有步骤后，整个服务网关Zuul应用就可以发挥作用了

四、总结

1.Spring Cloud对Netflix Zuul做了封装集成, 使得在Spring Cloud环境中使用Zuul更方便，只需添加spring-cloud-starter-zuul maven依赖及启动类上添加@EnableZuulProxy就可创建一个zuul应用。
2.Spring Cloud Zuul 实际上就是在Servlet的基础上添加了一些ZuulFilter去完成一些额外事情，封装了就成框架了。