zuul和spring集成分析。

zuul和spring集成

Zuul is implemented as a Servlet. For the general cases, Zuul is embedded into the Spring Dispatch mechanism. This lets Spring MVC be in control of the routing. In this case, Zuul buffers requests. If there is a need to go through Zuul without buffering requests (for example, for large file uploads), the Servlet is also installed outside of the Spring Dispatcher. By default, the servlet has an address of /zuul. This path can be changed with the zuul.servlet-path property.

zuul以servlet形式设计，集成到spring的DispatchServlet。

通过handler mapping形式，DispatchServlet把请求分发到zuul处理，依赖handler mapping。

protected void initStrategies(ApplicationContext context) {
	initMultipartResolver(context);
	initLocaleResolver(context);
	initThemeResolver(context);
    // handler映射
	initHandlerMappings(context);
	initHandlerAdapters(context);
	initHandlerExceptionResolvers(context);
	initRequestToViewNameTranslator(context);
	initViewResolvers(context);
	initFlashMapManager(context);
}

对于大文件上传这种服务，如果经过DispatcherServlet，会影响性能。因为DispatcherServlet为了方便后续处理流程使用，会将multipart/form请求根据RFC1867规则进行统一分析处理，并且返回MultipartHttpServletRequest实例，通过它可以获取file和其他参数。

网关通常来说不需要获取MultipartHttpServletRequest，特别是大文件，这样会比较影响性能，可以直接用ZuulServlet处理，参见ZuulServerAutoConfiguration：

@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<>();
    // zuul.servletPath
	filterRegistration.setUrlPatterns(
			Collections.singleton(this.zuulProperties.getServletPattern()));
	filterRegistration.setFilter(new ZuulServletFilter());
    // 优先级最低哦
	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;
}

zuul.use-filter是控制和spring整合的方式：

true： 默认配置，使用zuulServletFilter，先创建为FilterRegistrationBean，再注册到spring容器
false：使用zuulServlet，先创建为ServletRegistrationBean，再注册到servlet容器

值得留意的是buffer-requests。不管是ZuulServletFilter还是ZuulServlet，都由ZuulRunner对请求初始化。 bufferRequests决定是否包装request对象。

/**
 *
 * @param bufferRequests - whether to wrap the ServletRequest in HttpServletRequestWrapper and buffer the body.
 */
public ZuulRunner(boolean bufferRequests) {
    this.bufferRequests = bufferRequests;
}

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));
}

前面讲到大文件请求不应该包装。FormBodyWrapperFilter不对form和multipart包装：

application/x-www-form-urlencoded
multipart/form-data

public boolean shouldFilter() {
	RequestContext ctx = RequestContext.getCurrentContext();
	HttpServletRequest request = ctx.getRequest();
	String contentType = request.getContentType();
	// Don't use this filter on GET method
	if (contentType == null) {
		return false;
	}
	// Only use this filter for form data and only for multipart data in a
	// DispatcherServlet handler
	try {
		MediaType mediaType = MediaType.valueOf(contentType);
		return MediaType.APPLICATION_FORM_URLENCODED.includes(mediaType)
				|| (isDispatcherServletRequest(request)
						&& MediaType.MULTIPART_FORM_DATA.includes(mediaType));
	}
	catch (InvalidMediaTypeException ex) {
		return false;
	}
}

画了一张图，整理上面核心类的关系和流程：

zuul本地路由

把流量转发到本地zuul自定义的controller处理。使用forward路由：

zuul:
  sensitive-headers:
  routes:
    # 本地路由
    login-service:
      path: /rest_login/**
      url: forward:/rest_login