Springcloud的版本是Greenwich.SR2，Springboot版本是2.1.6.release.

最近使用到Springcloud的zuul，分析了下源码，记录下。

如下List-1，我们自己定义的ZuulFilter继承zuul的zuulFilter，之后定义为Bean，交给Spring容器:

List-1

//将过滤器交给Spring管理
@Bean
public AuthFilter authFilter(){return new AuthFilter();
}//xss过滤
@Bean
public XssFilter xssFilter(){return new XssFilter();
}@Bean
public HelloZuulFilter firewallFilter(){return new HelloZuulFilter();
}@Bean
public HelloInfoFilter helloInfoFilter(){return new HelloInfoFilter();
}

之后看下ZuulServerAutoConfiguration，如下List-2，@Autowired private Map<String, ZuulFilter> filters会从Spring容器中获取所有的ZuulFilter，之后实例化ZuulFilterInitializer时，将这个filters传入。

List-2

...
@Configuration
protected static class ZuulFilterConfiguration {@Autowiredprivate Map<String, ZuulFilter> filters;@Beanpublic ZuulFilterInitializer zuulFilterInitializer(CounterFactory counterFactory,TracerFactory tracerFactory) {FilterLoader filterLoader = FilterLoader.getInstance();FilterRegistry filterRegistry = FilterRegistry.instance();return new ZuulFilterInitializer(this.filters, counterFactory, tracerFactory,filterLoader, filterRegistry);}
}
...

如下List-3，

1. FilterRegistry是属性类型，contextInitialized方法上加了@PostConstruct，所以Spring创建这个Bean之后就会调用这个方法，遍历filters之后，放入filterRegistry中，filterRegistry中有个ConcurrentHashMap类型的属性，这些filter就是放入这个ConcurrentHashMap中。
2. 方法contextDestroyed上加了@PreDestroy注解，之后遍历filters，将其从filterRegistry中移除。

List-3

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;}@PostConstructpublic void contextInitialized() {log.info("Starting filter initializer");TracerFactory.initialize(tracerFactory);CounterFactory.initialize(counterFactory);for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) {filterRegistry.put(entry.getKey(), entry.getValue());}}@PreDestroypublic 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);}
...

默认会将ZuulServlet或者ZuulServletFilter注入到Spring容器中，如下如果设置zuul.use-filter为true，那么使用的是ZuulServletFilter，默认没有设置zuul.use-filter，所以使用的是ZuulServlet，如下List-4，ZuulServlet继承了HttpServlet，是个Servlet，之后交给ServletRegistrationBean，将这个ZuulServlet放入到web容器中。

List-4

...
@Bean
@ConditionalOnMissingBean(name = "zuulServlet")
@ConditionalOnProperty(name = "zuul.use-filter", havingValue = "false", matchIfMissing = true)
public ServletRegistrationBean zuulServlet() {ServletRegistrationBean<ZuulServlet> 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;
}@Bean
@ConditionalOnMissingBean(name = "zuulServletFilter")
@ConditionalOnProperty(name = "zuul.use-filter", havingValue = "true", matchIfMissing = false)
public FilterRegistrationBean zuulServletFilter() {final FilterRegistrationBean<ZuulServletFilter> filterRegistration = new FilterRegistrationBean<>();filterRegistration.setUrlPatterns(Collections.singleton(this.zuulProperties.getServletPattern()));filterRegistration.setFilter(new ZuulServletFilter());filterRegistration.setOrder(Ordered.LOWEST_PRECEDENCE);// The whole point of exposing this servlet is to provide a route that doesn't// buffer requests.filterRegistration.addInitParameter("buffer-requests", "false");return filterRegistration;
}
...

ZuulServlet的service方法如下，首先会调用preRoute()方法，之后调用route()，最后是postRoute()，preRoute方法调用了zuulRunner.preRoute()，ZuulRunner的preRoute()方法里面调用了FilterProcessor.getInstance().preRoute()，再深入FilterProcessor的preRoute方法，

List-5

public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {try {this.init((HttpServletRequest)servletRequest, (HttpServletResponse)servletResponse);RequestContext context = RequestContext.getCurrentContext();context.setZuulEngineRan();try {this.preRoute();} catch (ZuulException var13) {this.error(var13);this.postRoute();return;}try {this.route();} catch (ZuulException var12) {this.error(var12);this.postRoute();return;}try {this.postRoute();} catch (ZuulException var11) {this.error(var11);}} catch (Throwable var14) {this.error(new ZuulException(var14, 500, "UNHANDLED_EXCEPTION_" + var14.getClass().getName()));} finally {RequestContext.getCurrentContext().unset();}
}void postRoute() throws ZuulException {this.zuulRunner.postRoute();
}void route() throws ZuulException {this.zuulRunner.route();
}void preRoute() throws ZuulException {this.zuulRunner.preRoute();
}

FilterProcessor的preRoute()里面的代码如下List-6，调用runFilters方法，从FilterRegistry取出所有filterType是pre的所有ZuulFilter，之后进行排序，之后逐个调用ZuulFilter的runFilter方法——在方法processZuulFilter里面。ZuulFilter是个抽象类，runFilter方法里面调用了run方法，run方法是抽象方法，由我们自定义实现，如下List-7所示，

List-6

...
public void preRoute() throws ZuulException {try {this.runFilters("pre");} catch (ZuulException var2) {throw var2;} catch (Throwable var3) {throw new ZuulException(var3, 500, "UNCAUGHT_EXCEPTION_IN_PRE_FILTER_" + var3.getClass().getName());}
}public Object runFilters(String sType) throws Throwable {if (RequestContext.getCurrentContext().debugRouting()) {Debug.addRoutingDebug("Invoking {" + sType + "} type filters");}boolean bResult = false;List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);if (list != null) {for(int i = 0; i < list.size(); ++i) {ZuulFilter zuulFilter = (ZuulFilter)list.get(i);Object result = this.processZuulFilter(zuulFilter);if (result != null && result instanceof Boolean) {bResult |= (Boolean)result;}}}return bResult;
}public Object processZuulFilter(ZuulFilter filter) throws ZuulException {RequestContext ctx = RequestContext.getCurrentContext();boolean bDebug = ctx.debugRouting();String metricPrefix = "zuul.filter-";long execTime = 0L;String filterName = "";try {long ltime = System.currentTimeMillis();filterName = filter.getClass().getSimpleName();RequestContext copy = null;Object o = null;Throwable t = null;if (bDebug) {Debug.addRoutingDebug("Filter " + filter.filterType() + " " + filter.filterOrder() + " " + filterName);copy = ctx.copy();}ZuulFilterResult result = filter.runFilter();ExecutionStatus s = result.getStatus();execTime = System.currentTimeMillis() - ltime;switch(s) {case FAILED:t = result.getException();ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);break;case SUCCESS:o = result.getResult();ctx.addFilterExecutionSummary(filterName, ExecutionStatus.SUCCESS.name(), execTime);if (bDebug) {Debug.addRoutingDebug("Filter {" + filterName + " TYPE:" + filter.filterType() + " ORDER:" + filter.filterOrder() + "} Execution time = " + execTime + "ms");Debug.compareContextState(filterName, copy);}}if (t != null) {throw t;} else {this.usageNotifier.notify(filter, s);return o;}} catch (Throwable var15) {if (bDebug) {Debug.addRoutingDebug("Running Filter failed " + filterName + " type:" + filter.filterType() + " order:" + filter.filterOrder() + " " + var15.getMessage());}this.usageNotifier.notify(filter, ExecutionStatus.FAILED);if (var15 instanceof ZuulException) {throw (ZuulException)var15;} else {ZuulException ex = new ZuulException(var15, "Filter threw Exception", 500, filter.filterType() + ":" + filterName);ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);throw ex;}}
}
...

如下List-7所示，用try catch方式来调用run方法，如果run方法抛出异常，则视为失败，将ZuulFilterResult的ExecutionStatus设置为FAILED，所以我们实现的run方法返回什么值并不重要，重要的是不抛出异常，如果抛出异常则视为处理失败。

List-7

public ZuulFilterResult runFilter() {ZuulFilterResult zr = new ZuulFilterResult();if (!this.isFilterDisabled()) {if (this.shouldFilter()) {Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());try {Object res = this.run();zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS);} catch (Throwable var7) {t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed");zr = new ZuulFilterResult(ExecutionStatus.FAILED);zr.setException(var7);} finally {t.stopAndLog();}} else {zr = new ZuulFilterResult(ExecutionStatus.SKIPPED);}}return zr;
}

要注意的是，上面中涉及到的FilterRegistry引用的都是同一个静态变量，所以各个调用关系见不显示的传递，依然能确保线程安全。

private static final FilterRegistry INSTANCE = new FilterRegistry();

需要注意的是，ZuulServlet和ZuulServletFilter处理的是url为/zuul/*的请求，可以看List-4的this.zuulProperties.getServletPattern()，它的值就是/zuul，之后用ServletRegistration.Dynamic的addMapping方法加上处理的url为/zuul/*的。

Reference

1. 源码