springcloud zuul

zuul是springcloud的API网关。

入口也是springmvc的DispatcherServlet。

实际的handler是ZuulController，通过handleRequest方法调用了ZuulServlet的service方法来处理请求。

ZuulServlet就是一个普通的servlet，其service方法如下：

@Override
public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException {
    try {
        init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse);

        // 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();   //pre ZuulFilter在这里调用

        } catch (ZuulException e) {
            error(e);
            postRoute();
            return;
        }
        try {
            route();  //这里做路由
        } catch (ZuulException e) {
            error(e);
            postRoute(); //post ZuulFilter在这里调用

            return;
        }
        try {
            postRoute(); //post ZuulFilter在这里调用

        } catch (ZuulException e) {
            error(e);
            return;
        }

    } catch (Throwable e) {
        error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName()));
    } finally {
        RequestContext.getCurrentContext().unset();
    }
}