Servlet Filter

Understand the idea

doFilter can set encoding, check a condition, and call chain.doFilter to reach the next filter or resource. Returning without that call prevents downstream handling. Filters can centralize cross-cutting request work.

A concrete example

request.setCharacterEncoding("UTF-8");
chain.doFilter(request, response);

In the application

RequestFilter sets UTF-8 before parameter decoding and rejects invalid todo form tokens.

Order matters. Setting request encoding after reading form parameters is too late for that decoding.

See it in a working stage

• Stage 29: observe requests with a Servlet filter

Related concepts

• Servlet
• CSRF · Cross-Site Request Forgery
• Request parameters