Spring Cloud微服务网关Zuul过滤链的解析

╰半夏微凉° 2024-03-23 13:16 36阅读 0赞

## 一、Zuul过滤器的加载过程 ##

Zuul网关的Filter需要经过初始化加载到Spring容器后，才能在请求中发挥作用：

![format_png][]

在上篇文章：[《Spring Cloud微服务网关Zuul的注解@EnableZuulProxy或@EnableZuulServer做了什么事情》][Spring Cloud_Zuul_EnableZuulProxy_EnableZuulServer] 中说到的`ZuulServerAutoConfiguration`中有一个内部配置类`ZuulFilterConfiguration`就是Zuul中Filter初始化的入口：

@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);
       }
    }
    复制代码

**ZuulFilterInitializer**：

public class ZuulFilterInitializer {
    
       private static final Log log = LogFactory.getLog(ZuulFilterInitializer.class);
    
       private final Map<String, ZuulFilter> filters;
       private final CounterFactory counterFactory;
       private final TracerFactory tracerFactory;
       private final FilterLoader filterLoader;
       private final FilterRegistry filterRegistry;
    
       public ZuulFilterInitializer(Map<String, ZuulFilter> filters,
                             CounterFactory counterFactory,
                             TracerFactory tracerFactory,
                             FilterLoader filterLoader,
                             FilterRegistry filterRegistry) {
          this.filters = filters;
          this.counterFactory = counterFactory;
          this.tracerFactory = tracerFactory;
          this.filterLoader = filterLoader;
          this.filterRegistry = filterRegistry;
       }
    
       @PostConstruct
       public void contextInitialized() {
          log.info("Starting filter initializer");
    
          TracerFactory.initialize(tracerFactory);
          CounterFactory.initialize(counterFactory);
          // 将ZuulFilter放到FilterRegistry中
          for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) {
             filterRegistry.put(entry.getKey(), entry.getValue());
          }
       }
    
       @PreDestroy
       public void contextDestroyed() {
          log.info("Stopping filter initializer");
          for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) {
             filterRegistry.remove(entry.getKey());
          }
          clearLoaderCache();
    
          TracerFactory.initialize(null);
          CounterFactory.initialize(null);
       }
    
       private void clearLoaderCache() {
          Field field = ReflectionUtils.findField(FilterLoader.class, "hashFiltersByType");
          ReflectionUtils.makeAccessible(field);
          @SuppressWarnings("rawtypes")
          Map cache = (Map) ReflectionUtils.getField(field, filterLoader);
          cache.clear();
       }
    
    }
    复制代码

源码上可以看出，`FilterLoader`和`FilterRegistry`都是单例对象，然后把Spring容器中的所有`ZuulFilter`都交给`FilterRegistry`来管理，像Spring的单例池那样。`FilterRegistry`内部使用`ConcurrentHashMap`保存这些单例`ZuulFilter`。

在请求走到`ZuulServlet`的时候，会检查`ZuulRunner`是否初始化。如果没初始化，就去执行init方法初始化`ZuulRunner`；如果已经初始化，就进入service方法执行过滤链的逻辑。

`ZuulRunner`主要是对`RequestContext`的初始化，将请求上下文放入声明周期，以及获取`FilterProcessor`的单例对象，可以说是Zuul过滤链的执行器。最后在`FilterProcessor`中通过`FilterLoader`获取相应的Filter并初始化。

## 二、过滤链实现 ##

Zuul Filter主要分为前置过滤器(pre)、路由过滤器(route)和后置过滤器(post)。

[format_png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/7f3c58ede66540d5bed858f36fbef336.png
[Spring Cloud_Zuul_EnableZuulProxy_EnableZuulServer]: https://juejin.cn/post/7221576464408428599