先走filter,然後走servlet,然後回到filter，一個filter可以用chain.doFilter()分成前後兩部分。
filterA:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    System.out.println(1);
    chain.doFilter(request, response);
    System.out.println(2);
}
 

filterB:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    System.out.println(3);
    chain.doFilter(request, response);
    System.out.println(4);
  }

servletA:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out
 
.println("來到servlet了");
    response.getWriter().append("Served at: ").append(request.getContextPath());
  }

輸出結果是：
1
3
來到servlet了
4
2