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:

/module_name/controller_name/action_name, where:

module_name: path separated by slashes... Ex.: Submodule "Y" of Module "X": /X/Y controller_name: name of controller with no special chars action_name: name of action with no special chars

I would like map /module_name/controller_name/ to a specific servlet controller! Action part is a public method on that class! :)

How I could do this? Using filters? I want an example, if possible!

score 14 · Accepted Answer · answered Jul 27 '12 at 06:05

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

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

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)

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

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