How to make a URL filter to route actions with Servlets?

Question

I\'m currently developing a Java EE web framework and I would want to know how I could route my URL\'s... I want support HMVC feature! URL\'s will follow this rule:

/mod

Answer 1

i see 3 ways: filter, basic servlet(all requests via main servlet) or "servlet-mapping"

filter

This example rewrite url

http://example.org/<int value>

to

http://example.org/user?id=<int value>

i.e

http://example.org/1234 -> http://example.org/user?id=1234

1. determinate filter in web.xml

<filter>
    <filter-name>Router</filter-name>
    <filter-class>org.example.Router</filter-class>
    <init-param>
        <param-name>param1</param-name>
        <param-value>valueOfparam1</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>Router</filter-name>
    <url-pattern>/*</url-pattern> 
</filter-mapping>

in init-param section you can specify route rules

1. filter class

   public class Router implements javax.servlet.Filter {
   
   private static final Pattern REWRITE_PATTERN = Pattern.compile("(^[1-9]\\d*)$");
   
   @Override
   public void destroy() {
   }
   
   @Override
   public void doFilter(ServletRequest req, ServletResponse res, FilterChain fc) throws IOException, ServletException {
   //this method calling before controller(servlet), every request
   
       HttpServletRequest request = (HttpServletRequest) req;
       String url = request.getRequestURL().toString();
       String number = url.substring(url.lastIndexOf("/")).replace("/", "");
   
       Matcher m = REWRITE_PATTERN.matcher(number);
       if(m.find()) {
           RequestDispatcher dispatcher = request.getRequestDispatcher("user?id=" + m.group(1));
           dispatcher.forward(req, res);
       } else {
           fc.doFilter(req, res);
       }
   }
   
   @Override
   public void init(FilterConfig fc) throws ServletException {
       //here you may read params from web.xml
   }}
   

basic sevlet

public class BasicServlet extends HttpServlet {
   //route rules here, and rewrite
}

servlet-mapping

<servlet-mapping>
    <servlet-name>UserServlet</servlet-name>
    <uri-mapping>/user/*</uri-mapping>
</servlet-mapping>
<servlet-mapping>
    <servlet-name>PostServlet</servlet-name>
    <uri-mapping>/post/*</uri-mapping>
</servlet-mapping>

• filter - more flexible and not require serious modify working code
• basic servlet - flexible, require change you code
• servlet mapping - simply, not flexible(for specific route rules)