Spring Cloud Netflix Zuul

1. FilterConstants

在org.springframework.cloud.netflix.zuul.filters.support.FilterConstants中，可以看到Zuul定义了Filter的类型（Type）。

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public final class FilterConstants {
  
  //省略...
  
  // Zuul Filter TYPE constants -----------------------------------

	/**
	 * {@link ZuulFilter#filterType()} error type.
	 */
	public static final String ERROR_TYPE = "error";

	/**
	 * {@link ZuulFilter#filterType()} post type.
	 */
	public static final String POST_TYPE = "post";

	/**
	 * {@link ZuulFilter#filterType()} pre type.
	 */
	public static final String PRE_TYPE = "pre";

	/**
	 * {@link ZuulFilter#filterType()} route type.
	 */
	public static final String ROUTE_TYPE = "route";
  
  //省略...
  
}

2. ZuulServlet

在com.netflix.zuul.http.ZuulServlet中，可以看到不同类型的Filter的执行顺序。

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public class ZuulServlet extends HttpServlet {
  
    //省略...

    @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();
            } 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();
        }
    }
  
    //省略...
  
}