Zuul源码分析

ZUUL

ZUUL功能如下：

• 认证

• 动态路由

• 安全

• 静态response处理

• 压力测试

• 流控

核心概念

• type: 用于定义routing过程的各个阶段。

• 执行优先级：同一类型的Filter下filter的执行顺序。

• critria: filter被执行满足的条件。

• action: criteria满足后待执行的action。

ZuulFilter和IZuulFilter的核心接口:

//filter执行的满足条件
shoudFilter()
//filter的执行逻辑
run()
//filter类别
filterType()
//同类别filter的执行优先级
filterOrder()</pre>

看request的生命过程，http request在进入原始前先执行pre类型额filter。routing filter路由请求到后台的服务并处理服务返回的结果。post类型的filter则是执行事后分析。整个过程如下图所示：

image

重要的类

• ZuulServlet
  实现了Servlet，将Zuul嵌入到Spring的Dispatch机制中。让spring mvc控制routing。
• SimpleRouteLocator
  加载路由配置
• RequestContext
  用于多个Filter之间共享信息，各个请求的数据存在ThreadLocal。
• ZuulProxyConfiguration
  注入各类Filter
• SimpleHostRoutingFilter
  路由请求到后台处理

源码分析

看demo代码，首先找到入口

@SpringBootApplication
@EnableEurekaClient
@EnableZuulProxy
public class SpringZuulApplication {
  public static void main(String[] args) {
    SpringApplication.run(SpringZuulApplication.class, args);
  }

}

• EnableZuulProxy类是关键，这个是走查源码的入口

@EnableCircuitBreaker
@EnableDiscoveryClient
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(ZuulProxyConfiguration.class)
public @interface EnableZuulProxy {
}

顺着该类看到了ZuulProxyAutoConfiguration，类中注入了DiscoveryClient,ServiceRouteMapper,Registration

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

    @Autowired(required = false)
    private Registration registration;

    @Autowired
    private DiscoveryClient discovery;

    @Autowired
    private ServiceRouteMapper serviceRouteMapper;

还注入了PreDecorationFilter,RibbonRoutingFilter,SimpleHostRoutingFilter等。也就是注入了一些内置额pre,route,post类型的filter。

从源码不难发现，ZuulProxyAutoConfiguration集成了ZuulServerAutoConfiguration类

public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration {

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

    @Autowired(required = false)
    private Registration registration;

    @Autowired
    private DiscoveryClient discovery;

    @Autowired
    private ServiceRouteMapper serviceRouteMapper;
}

我们看下ZuulServerAutoConfiguration类做了什么事情。
打开ZuulServerAutoConfiguration的实现，发现注入了一些bean，比如SimpleRouteLocator，ZuulController,ZuulHandlerMapping,ZuulRefreshListener，还有ServletDetectionFilter,SendResponseFilter,SendErrorFilter等通用过滤器。

    // 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;
        }

    }

最为重要的是

@Configuration
protected static class ZuulFilterConfiguration

在该配置类中，注入了ZuulFilterInitializer对象，该对象中完成Filter的注册（查看@PostConstruct）。
自此Zuul完成了配置的初始化。

流程

说了一堆，一个请求进来，是如何经过Zuul处理的咧。这就需要用到ZuulServlet这个类了，该类实现了HttpServlet。重写的service方法中，使用了模板设计模式，依次调用了

preRoute()
route()
postRoute()

ZuulServlet中持有一个ZuulRunner对象，该对象调用了FilterProcessor的preRoute(),route()以及postRoute()。为了代码的复用，以上的方法均调用runFilters(String sType)方法

 List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
for(int i=0; i<list.size; i++){
    processZuulFilter(zuulFilter);
}

FilterLoader类中持有FilterRegistry对象获取之前注册上的所有Filter。自此整个过程分析完毕。