ZuulServlet源码分析及ZuulFilter加载

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

1.声明ZuulServlet

@Configuration
@EnableConfigurationProperties({ZuulProperties.class})
@ConditionalOnClass(ZuulServlet.class)  --->[ConditionalOnClass详解](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;
    }
}

以上通过 ServletRegistrationBean servlet = new ServletRegistrationBean(new ZuulServlet(),this.zuulProperties.getServletPattern()); 使用配置的URL mapping实例化一个Servlet,其中URL mapping在 application.properties 文件中配置，例如:

#拦截路径
zuul.servletPath=/openapi/

以上实现了 /openapi/ 被 ZuulServlet 处理的逻辑。

2.ZuulServlet处理逻辑

当请求path为 /openapi/ 的请求进入网关后，就会被 ZuulServlet 处理,以下为 ZuulServlet 处理流程:

public class ZuulServlet extends HttpServlet {

    private static final long serialVersionUID = -3374242278843351500L;
    private ZuulRunner zuulRunner; //ZuulServlet逻辑真正的实现类

    @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);//将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() 会在ZuulRunner中将 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() 方法通过 zuulRunner 的 preRoute() 实现; zuulRunner 的 preRoute() 通过调用 FilterProcessor.getInstance().preRoute() 实现; FilterProcessor 的 preRoute() 执行自身 runFilters("pre") 方法执行 prefilter ; runFilters("pre") 方法会从 FilterLoader.getInstance().getFiltersByType(sType) 中过滤出pre filter循环执行 processZuulFilter(zuulFilter) ，以下为服务调用层次关系。

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();//执行filter，其中包括filter是否需要执行(shouldFilter())
//filterRegistry为单例模式，通过FilterRegistry.instance()获取实例，getAllFilters()方法获取类型为ConcurrentHashMap<String, ZuulFilter>的filters。

3.ZuulFilter 加载

针对上述代码中的 FilterRegistry 中的filters需要在项目启动时，显示声明进行初始化：

 @Configuration
    protected static class ZuulFilterConfiguration {

        //按类型将所有ZuulFilter注入到map中
        @Autowired
        private Map<String, ZuulFilter> filters;

        @Bean
        public ZuulFilterInitializer zuulFilterInitializer() {
            return new ZuulFilterInitializer(this.filters); //将项目中的ZuulFilter存入FilterRegistry.instance()的filters中
        }

    }

其中 ZuulFilterInitializer 为实现了 ServletContextListener 类，会根据项目声明在项目启动时进行对 FilterRegistry.instance() 的 filters 进行初始化。

@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());
        }
    }
    ..........后继代码省略
 }

4.其他

ZuulServlet 的 route() 、 postRoute() 、 error(e) 方法执行逻辑与 preRoute() 相同。