How is it possible that Filter is applied when its dispatcher is FORWARD as well as when dispatcher is REQUEST?

问题

I have a simple Filter:

public class TestFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("before");
        chain.doFilter(request, response);
        System.out.println("after");
    }

    public void destroy() {
    }

}

It's the first filter in web.xml and it has one of these two mappings:

<filter-mapping>
    <filter-name>cookie-test-filter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>

<filter-mapping>
    <filter-name>cookie-test-filter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

In both cases I see the output:

before
before
after
after

(I've also tried INCLUDE as dispatcher just to be sure that everything works - there's no output with INCLUDE).

There're 3rd-party filters and servlets after this filter and I wonder: what should they do to make my filter applied in both described cases?

回答1:

Try using a single <filter-mapping> entry with both REQUEST and FORWARD dispatcher

Example

<filter-mapping>
    <filter-name>cookie-test-filter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

Hope this clears up the issue you were having.

来源：https://stackoverflow.com/questions/5325405/how-is-it-possible-that-filter-is-applied-when-its-dispatcher-is-forward-as-well

标签

java

servlets

servlet-filters

dispatcher