Can we use regular expressions in web.xml URL patterns?

No, you can't use a regex there. According to the Java Servlet Specification v2.4 (section srv.11.1), the url-path is interpreted as follows:

A string beginning with a ‘/’ character and ending with a ‘/*’ suffix is used for path mapping.

A string beginning with a ‘*.’ prefix is used as an extension mapping.

A string containing only the ’/’ character indicates the "default" servlet of the application. In this case the servlet path is the request URI minus the con- text path and the path info is null.

All other strings are used for exact matches only.

No regexes are allowed. Not even complicated wild-cards.

As noted by others, there is no way to filter with regular expression matching using only the basic servlet filter features. The servlet spec is likely written the way it is to allow for efficient matching of urls, and because servlets predate the availability of regular expressions in java (regular expressions arrived in java 1.4).

Regular expressions would likely be less performant (no I haven't benchmarked it), but if you are not strongly constrained by processing time and wish to trade performance for ease of configuration you can do it like this:

In your filter:

private String subPathFilter = ".*";
private Pattern pattern;

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    String subPathFilter = filterConfig.getInitParameter("subPathFilter");
    if (subPathFilter != null) {
      this.subPathFilter = subPathFilter;
    }
    pattern = Pattern.compile(this.subPathFilter);
  }

  public static String getFullURL(HttpServletRequest request) {
    // Implement this if you want to match query parameters, otherwise 
    // servletRequest.getRequestURI() or servletRequest.getRequestURL 
    // should be good enough. Also you may want to handle URL decoding here.
  }

  @Override
  public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    Matcher m = pattern.matcher(getFullURL((HttpServletRequest) servletRequest));
    if (m.matches()) {

      // filter stuff here.

    }
  }

Then in web.xml...

  <filter>
    <filter-name>MyFiltersName</filter-name>
    <filter-class>com.example.servlet.MyFilter</filter-class>
    <init-param>
      <param-name>subPathFilter</param-name>
      <param-value>/org/test/[^/]+/keys/.*</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>MyFiltersName</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

It's also sometimes convenient to make the pattern exclude the match by inverting the if statement in doFilter() (or add another init param for excludes patterns, which is left as an exercise for the reader.)

Can we use regular expressions in web.xml URL patterns?

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