ZuulServlet源碼分析及ZuulFilter加載

參考
https://yq.aliyun.com/wenji/2...
https://blog.csdn.net/lds2227...

1.聲明ZuulServlet

@Configuration @EnableConfigurationProperties({ZuulProperties.class}) @ConditionalOnClass(ZuulServlet.class)  --->[ConditionalOnClass詳解](https://412887952-qq-com.iteye.com/blog/2395065)
@Import(ServerPropertiesAutoConfiguration.class) public class ZuulConfigurationCustom { @Autowired protected ZuulProperties zuulProperties; @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; } }

以上通過 ServletRegistrationBean servlet = new ServletRegistrationBean(new ZuulServlet(),this.zuulProperties.getServletPattern()); 使用配置的URL mapping實例化一個Servlet,其中URL mapping在 application.properties 文件中配置，例如:

#攔截路徑 zuul.servletPath=/openapi/

以上實現了 /openapi/ 被 ZuulServlet 處理的邏輯。

2.ZuulServlet處理邏輯

當請求path為 /openapi/ 的請求進入網關后，就會被 ZuulServlet 處理,以下為 ZuulServlet 處理流程:

public class ZuulServlet extends HttpServlet { private static final long serialVersionUID = -3374242278843351500L; private ZuulRunner zuulRunner; //ZuulServlet邏輯真正的實現類
 @Override public void init(ServletConfig config) throws ServletException { super.init(config); String bufferReqsStr = config.getInitParameter("buffer-requests"); boolean bufferReqs = bufferReqsStr != null && bufferReqsStr.equals("true") ? true : false; zuulRunner = new ZuulRunner(bufferReqs); } @Override public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException { try { init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse);//將servletRequest和servletResponse存入RequestContext(RequestContext.getCurrentContext()) // Marks this request as having passed through the "Zuul engine", as opposed to servlets // explicitly bound in web.xml, for which requests will not have the same data attached
            RequestContext context = RequestContext.getCurrentContext(); context.setZuulEngineRan(); try { preRoute(); } catch (ZuulException e) { error(e); postRoute(); return; } try { route(); } catch (ZuulException e) { error(e); postRoute(); return; } try { postRoute(); } catch (ZuulException e) { error(e); return; } } catch (Throwable e) { error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName())); } finally { RequestContext.getCurrentContext().unset(); } } /** * executes "post" ZuulFilters * * @throws ZuulException */
    void postRoute() throws ZuulException { zuulRunner.postRoute(); } /** * executes "route" filters * * @throws ZuulException */
    void route() throws ZuulException { zuulRunner.route(); } /** * executes "pre" filters * * @throws ZuulException */
    void preRoute() throws ZuulException { zuulRunner.preRoute(); } /** * initializes request * * @param servletRequest * @param servletResponse */
    void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { zuulRunner.init(servletRequest, servletResponse); } /** * sets error context info and executes "error" filters * * @param e */
    void error(ZuulException e) { RequestContext.getCurrentContext().setThrowable(e); zuulRunner.error(); } }

以上 service() 方法中 init() 會在ZuulRunner中將 servletRequest 和 servletResponse 存入 RequestContext(RequestContext.getCurrentContext()) ，如下：

public void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { RequestContext ctx = RequestContext.getCurrentContext(); if (bufferRequests) { ctx.setRequest(new HttpServletRequestWrapper(servletRequest)); } else { ctx.setRequest(servletRequest); } ctx.setResponse(new HttpServletResponseWrapper(servletResponse)); }

 ZuulServlet 的 preRoute() 方法通過 zuulRunner 的 preRoute() 實現; zuulRunner 的 preRoute() 通過調用 FilterProcessor.getInstance().preRoute() 實現; FilterProcessor 的 preRoute() 執行自身 runFilters("pre") 方法執行 prefilter ; runFilters("pre") 方法會從 FilterLoader.getInstance().getFiltersByType(sType) 中過濾出pre filter循環執行 processZuulFilter(zuulFilter) ，以下為服務調用層次關系。

ZuulServlet.preRoute(); |_____ zuulRunner.preRoute(); |_____ FilterProcessor.getInstance().preRoute(); |_____ runFilters("pre"); |_____ List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType); |       |_____ Collection<ZuulFilter> filters = filterRegistry.getAllFilters(); |_____ processZuulFilter(zuulFilter); |_____ ZuulFilterResult result = filter.runFilter();//執行filter，其中包括filter是否需要執行(shouldFilter()) //filterRegistry為單例模式，通過FilterRegistry.instance()獲取實例，getAllFilters()方法獲取類型為ConcurrentHashMap<String, ZuulFilter>的filters。

3.ZuulFilter 加載

針對上述代碼中的 FilterRegistry 中的filters需要在項目啟動時，顯示聲明進行初始化：

 @Configuration protected static class ZuulFilterConfiguration { //按類型將所有ZuulFilter注入到map中
 @Autowired private Map<String, ZuulFilter> filters; @Bean public ZuulFilterInitializer zuulFilterInitializer() { return new ZuulFilterInitializer(this.filters); //將項目中的ZuulFilter存入FilterRegistry.instance()的filters中
 } }

其中 ZuulFilterInitializer 為實現了 ServletContextListener 類，會根據項目聲明在項目啟動時進行對 FilterRegistry.instance() 的 filters 進行初始化。

@CommonsLog public class ZuulFilterInitializer implements ServletContextListener { private Map<String, ZuulFilter> filters; public ZuulFilterInitializer(Map<String, ZuulFilter> filters) { this.filters = filters; } @Override public void contextInitialized(ServletContextEvent sce) { log.info("Starting filter initializer context listener"); // FIXME: mocks monitoring infrastructure as we don't need it for this simple app
 MonitoringHelper.initMocks(); FilterRegistry registry = FilterRegistry.instance(); for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) { registry.put(entry.getKey(), entry.getValue()); } } ..........后繼代碼省略 }

4.其他

 ZuulServlet 的 route() 、 postRoute() 、 error(e) 方法執行邏輯與 preRoute() 相同。