Springcloud中zuul的Zuul Filter是什么，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
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 { @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); } } ...如下List-3，
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。
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; } @PostConstruct public 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()); } } @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); } ...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。
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