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;
}
作者：David_jim
链接：https://www.jianshu.com/p/295e51bc1518