浅谈Spring Cloud zuul http请求转发原理

spring cloud 网关，依赖于netflix 下的zuul 组件

zuul 的流程是，自定义 了ZuulServletFilter和zuulServlet两种方式，让开发者可以去实现，并调用

先来看下ZuulServletFilter的实现片段

 @Override
  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    try {
      init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse);
      try {
        preRouting();
      } catch (ZuulException e) {
        error(e);
        postRouting();
        return;
      }

      // Only forward onto to the chain if a zuul response is not being sent
      if (!RequestContext.getCurrentContext().sendZuulResponse()) {
        filterChain.doFilter(servletRequest, servletResponse);
        return;
      }

      try {
        routing();
      } catch (ZuulException e) {
        error(e);
        postRouting();
        return;
      }
      try {
        postRouting();
      } catch (ZuulException e) {
        error(e);
        return;
      }
    } catch (Throwable e) {
      error(new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_FROM_FILTER_" + e.getClass().getName()));
    } finally {
      RequestContext.getCurrentContext().unset();
    }
  }

从上面的代码可以看到，比较关心的是preRouting、routing,postRouting三个方法 ，这三个方法会调用 注册为ZuulFilter的子类，首先来看下这三个方法

preRouting: 是路由前会做一些内容

routing():开始路由事项

postRouting：路由结束，不管是否有错误都会经过该方法

那这三个方法是怎么和ZuulFilter联系在一起的呢？

先来分析下 preRouting:

 void postRouting() throws ZuulException {
    zuulRunner.postRoute();
  }

同时 ZuulRunner再来调用

  public void postRoute() throws ZuulException {
    FilterProcessor.getInstance().postRoute();
  }

最终调用 FilterProcessor 的 runFilters

  public void preRoute() throws ZuulException {
    try {
      runFilters("pre");
    } catch (ZuulException e) {
      throw e;
    } catch (Throwable e) {
      throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_PRE_FILTER_" + e.getClass().getName());
    }
  }

看到了runFilters 是通过 filterType(pre ,route ,post )来过滤出已经注册的 ZuulFilter:

 public Object runFilters(String sType) throws Throwable {
    if (RequestContext.getCurrentContext().debugRouting()) {
      Debug.addRoutingDebug("Invoking {" + sType + "} type filters");
    }
    boolean bResult = false;
    //通过sType获取 zuulFilter的列表
    List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
    if (list != null) {
      for (int i = 0; i < list.size(); i++) {
        ZuulFilter zuulFilter = list.get(i);
        Object result = processZuulFilter(zuulFilter);
        if (result != null && result instanceof Boolean) {
          bResult |= ((Boolean) result);
        }
      }
    }
    return bResult;
  }

再来看下 ZuulFilter的定义

public abstract class ZuulFilter implements IZuulFilter, Comparable<ZuulFilter> {

  private final DynamicBooleanProperty filterDisabled =
      DynamicPropertyFactory.getInstance().getBooleanProperty(disablePropertyName(), false);

  /**
   * to classify a filter by type. Standard types in Zuul are "pre" for pre-routing filtering,
   * "route" for routing to an origin, "post" for post-routing filters, "error" for error handling.
   * We also support a "static" type for static responses see StaticResponseFilter.
   * Any filterType made be created or added and run by calling FilterProcessor.runFilters(type)
   *
   * @return A String representing that type
   */
  abstract public String filterType();

  /**
   * filterOrder() must also be defined for a filter. Filters may have the same filterOrder if precedence is not
   * important for a filter. filterOrders do not need to be sequential.
   *
   * @return the int order of a filter
   */
  abstract public int filterOrder();

  /**
   * By default ZuulFilters are static; they don't carry state. This may be overridden by overriding the isStaticFilter() property to false
   *
   * @return true by default
   */
  public boolean isStaticFilter() {
    return true;
  }

只列出了一部分字段，但可以看到filterType和filterOrder两个字段，这两个分别是指定filter是什么类型，排序

这两个决定了实现的ZuulFilter会在什么阶段被执行，按什么顺序执行

当选择好已经注册的ZuulFilter后，会调用ZuulFilter的runFilter

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

其中run 是一个ZuulFilter的一个抽象方法

public interface IZuulFilter {
  /**
   * a "true" return from this method means that the run() method should be invoked
   *
   * @return true if the run() method should be invoked. false will not invoke the run() method
   */
  boolean shouldFilter();

  /**
   * if shouldFilter() is true, this method will be invoked. this method is the core method of a ZuulFilter
   *
   * @return Some arbitrary artifact may be returned. Current implementation ignores it.
   */
  Object run();
}

所以，实现ZuulFilter的子类要重写 run方法，我们来看下 其中一个阶段的实现 PreDecorationFilter 这个类是Spring Cloud封装的在使用Zuul 作为转发的代码服务器时进行封装的对象，目的是为了决定当前的要转发的请求是按ServiceId，Http请求，还是forward来作转发

@Override
  public Object run() {
    RequestContext ctx = RequestContext.getCurrentContext();
    final String requestURI = this.urlPathHelper.getPathWithinApplication(ctx.getRequest());
    Route route = this.routeLocator.getMatchingRoute(requestURI);
    if (route != null) {
      String location = route.getLocation();
      if (location != null) {
        ctx.put("requestURI", route.getPath());
        ctx.put("proxy", route.getId());
        if (!route.isCustomSensitiveHeaders()) {
          this.proxyRequestHelper
              .addIgnoredHeaders(this.properties.getSensitiveHeaders().toArray(new String[0]));
        }
        else {
          this.proxyRequestHelper.addIgnoredHeaders(route.getSensitiveHeaders().toArray(new String[0]));
        }

        if (route.getRetryable() != null) {
          ctx.put("retryable", route.getRetryable());
        }
        // 如果配置的转发地址是http开头，会设置 RouteHost
        if (location.startsWith("http:") || location.startsWith("https:")) {
          ctx.setRouteHost(getUrl(location));
          ctx.addOriginResponseHeader("X-Zuul-Service", location);
        }
         // 如果配置的转发地址forward，则会设置forward.to
        else if (location.startsWith("forward:")) {
          ctx.set("forward.to",
              StringUtils.cleanPath(location.substring("forward:".length()) + route.getPath()));
          ctx.setRouteHost(null);
          return null;
        }
        else {
           // 否则以serviceId进行转发
          // set serviceId for use in filters.route.RibbonRequest
          ctx.set("serviceId", location);
          ctx.setRouteHost(null);
          ctx.addOriginResponseHeader("X-Zuul-ServiceId", location);
        }
        if (this.properties.isAddProxyHeaders()) {
          addProxyHeaders(ctx, route);
          String xforwardedfor = ctx.getRequest().getHeader("X-Forwarded-For");
          String remoteAddr = ctx.getRequest().getRemoteAddr();
          if (xforwardedfor == null) {
            xforwardedfor = remoteAddr;
          }
          else if (!xforwardedfor.contains(remoteAddr)) { // Prevent duplicates
            xforwardedfor += ", " + remoteAddr;
          }
          ctx.addZuulRequestHeader("X-Forwarded-For", xforwardedfor);
        }
        if (this.properties.isAddHostHeader()) {
          ctx.addZuulRequestHeader("Host", toHostHeader(ctx.getRequest()));
        }
      }
    }
    else {
      log.warn("No route found for uri: " + requestURI);

      String fallBackUri = requestURI;
      String fallbackPrefix = this.dispatcherServletPath; // default fallback
                                // servlet is
                                // DispatcherServlet

      if (RequestUtils.isZuulServletRequest()) {
        // remove the Zuul servletPath from the requestUri
        log.debug("zuulServletPath=" + this.properties.getServletPath());
        fallBackUri = fallBackUri.replaceFirst(this.properties.getServletPath(), "");
        log.debug("Replaced Zuul servlet path:" + fallBackUri);
      }
      else {
        // remove the DispatcherServlet servletPath from the requestUri
        log.debug("dispatcherServletPath=" + this.dispatcherServletPath);
        fallBackUri = fallBackUri.replaceFirst(this.dispatcherServletPath, "");
        log.debug("Replaced DispatcherServlet servlet path:" + fallBackUri);
      }
      if (!fallBackUri.startsWith("/")) {
        fallBackUri = "/" + fallBackUri;
      }
      String forwardURI = fallbackPrefix + fallBackUri;
      forwardURI = forwardURI.replaceAll("//", "/");
      ctx.set("forward.to", forwardURI);
    }
    return null;
  }

这个前置处理，是为了后面决定以哪种ZuulFilter来处理当前的请求 ，如 SimpleHostRoutingFilter，这个的filterType是post ,当 ``PreDecorationFilter设置了requestContext中的 RouteHost，如 SimpleHostRoutingFilter中的判断

  @Override
  public boolean shouldFilter() {
    return RequestContext.getCurrentContext().getRouteHost() != null
        && RequestContext.getCurrentContext().sendZuulResponse();
  }

在 SimpleHostRoutingFilter中的run中，真正实现地址转发的内容，其实质是调用 httpClient进行请求

@Override
  public Object run() {
    RequestContext context = RequestContext.getCurrentContext();
    HttpServletRequest request = context.getRequest();
    MultiValueMap<String, String> headers = this.helper
        .buildZuulRequestHeaders(request);
    MultiValueMap<String, String> params = this.helper
        .buildZuulRequestQueryParams(request);
    String verb = getVerb(request);
    InputStream requestEntity = getRequestBody(request);
    if (request.getContentLength() < 0) {
      context.setChunkedRequestBody();
    }

    String uri = this.helper.buildZuulRequestURI(request);
    this.helper.addIgnoredHeaders();

    try {
      HttpResponse response = forward(this.httpClient, verb, uri, request, headers,
          params, requestEntity);
      setResponse(response);
    }
    catch (Exception ex) {
      context.set(ERROR_STATUS_CODE, HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
      context.set("error.exception", ex);
    }
    return null;
  }

最后如果是成功能，会调用 注册 为post的ZuulFilter ,目前有两个 SendErrorFilter 和 SendResponseFilter 这两个了，一个是处理错误，一个是处理成功的结果

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。