Develop servlet filters for form login processing



You can control the look and feel of the login screen using the form-based login mechanism. In form-based login, you specify a login page that is used to retrieve the user ID and password information. You also can specify an error page that displays when authentication fails.

If additional authentication or additional processing is required before and after authentication, servlet filters are an option. Servlet filters can dynamically intercept requests and responses to transform or use the information contained in the requests or responses. One or more servlet filters can be attached to a servlet or a group of servlets. Servlet filters also can attach to JavaServer Pages (JSP) files and HTML pages. All the attached servlet filters are called before the servlet is invoked.

Both form-based login and servlet filters are supported by any servlet version 2.3 specification complaint Web container. The form login servlet performs the authentication and servlet filters perform additional authentication, auditing, or logging information.

To perform pre-login and post-login actions using servlet filters, configure these filters for either form login page support or for the /j_security_check URL. The j_security_check is posted by a form login page with the j_username parameter containing the user name and the j_password parameter containing the password. A servlet filter can use the user name parameter and password information to perform more authentication or other special needs.


Step for this task

A servlet filter implements the javax.servlet.Filter class. There are three methods in the filter class that need implementing:

If a servlet maps to many servlet filters, servlet filters are called in the order that is listed in the deployment descriptor of the application (web.xml).

An example of a servlet filter follows: This login filter can map to /j_security_check to perform pre-login and post-login actions.

import javax.servlet.*;

public class LoginFilter implements Filter {

protected FilterConfig filterConfig;

// Called once when this filter is instantiated.
// If mapped to j_security_check, called
// very first time j_security_check is invoked.
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;

public void destroy() {
this.filterConfig = null;

// Called for every request that is mapped to this filter.
// If mapped to j_security_check,
// called for every j_security_check action
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws, ServletException {

// perform pre-login action here

chain.doFilter(request, response);
// calls the next filter in chain.

// j_security_check if this filter is

// mapped to j_security_check.

// perform post-login action here.

} Place the servlet filter class file in the WEB-INF/classes directory of the application.


See also

Example: Servlet filters


See Also

Accessing the Samples (Samples Gallery)


Related Tasks

Developing form login pages
Securing Web applications using an assembly tool