Working with Servlets and Servlet Filters

Spring Cloud Gateway Server MVC is built for Servlet-stack web applications built on the Servlet API and deployed to Servlet containers. If your applications uses Servlets or Servlet Filters you may need to take care in their ordering.

Because of the way Servlet Containers handle request parameters, when a Spring WebMVC application receives a content type of application/x-www-form-urlencoded, Servlet containers combine those with query parameters into "request" parameters. A special FormFilter bean is included in Spring Cloud Gateway Server MVC to rebuild the form body for downstream applications. Any Servlet Filter that reads request parameters before the filter chain is run will need to be ordered before FormFilter. See the example below.

MyFilter.java

import jakarta.servlet.Filter;
import org.springframework.cloud.gateway.server.mvc.filter.FormFilter;
import org.springframework.core.Ordered;

class MyFilter implements Filter, Ordered {

    @Override
    public int getOrder() {
        return FormFilter.FORM_FILTER_ORDER - 1;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {
        // ...
        filterChain.doFilter(request, response);
        // ...
    }
}