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🔔 Subscribe to Ram N JavaWhat is FilterChain in Java Servlets?
In Java web applications, the FilterChain interface (provided by javax.servlet) represents the invocation sequence of multiple filters applied to a particular web resource, such as a servlet or JSP page.
When a browser makes an HTTP request that matches several configured filters, the servlet container does not execute them in isolation. Instead, it constructs a FilterChain object and passes it to each filter's doFilter() method. This mechanism allows multiple filters to intercept, inspect, and modify the request and response in an organized, stepwise sequence.
How the doFilter Method Works
The FilterChain interface defines a single, crucial method:
public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException;
When a filter calls chain.doFilter(request, response), one of two things happens:
- If another filter exists in the chain: The web container invokes the next filter in line.
- If it is the last filter in the chain: The web container invokes the destination servlet or web resource itself.
If a filter decides not to invoke chain.doFilter(), the execution halts immediately. This is commonly used in authentication or validation filters to block unauthorized access from reaching the target servlet.
Execution Order and Lifecycle Flow
- Order of Execution: The servlet container determines filter invocation order based strictly on the sequence of
<filter-mapping>entries inweb.xml. - Symmetrical Two-Way Processing: Code placed before
chain.doFilter()runs on the way in (request phase), while code placed afterchain.doFilter()runs on the way back (response phase). - Clean Decoupling: Individual tasks like logging, authorization, and character encoding remain cleanly separated into focused, reusable components.
Recommended Related Tutorials
Continue exploring servlet filters and web architecture with these tutorials from Ram N Java:
Click here to watch in Youtube : https://www.youtube.com/watch?v=ADI9IMivvKA
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