Decorator Pattern Filter in the Spring Framework

In the Spring framework, the decorator pattern is widely used in the implementation of Filter. Filter is a component in the Servlet specification used for pre processing and post processing requests and responses. In the Spring framework, Filter adopts the decorator mode to enhance its functionality. Specifically, the Filter in the Spring framework consists of the abstract class OncePerRequestFilter and the implementation class ConcreteFilter, with OncePerRequestFilter serving as the abstract decorator and ConcreteFilter serving as the concrete decorator. OncePerRequestFilter provides an abstract method, doFilterInternal, in which specific filtering logic is defined. This method accepts ServletRequest and ServletResponse objects as parameters and can perform any operation on them. The concrete decorator ConcreteFilter inherits from OncePerRequestFilter and implements the doFilterInternal method. In the implementation, ConcreteFilter can perform some preprocessing operations, then call the doFilterInternal method of the parent class, and finally perform some post-processing operations. The following is the complete source code of the Filter decorator mode in the Spring framework: public abstract class OncePerRequestFilter implements Filter { @Override public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException { HttpServletRequest httpRequest = (HttpServletRequest) request; HttpServletResponse httpResponse = (HttpServletResponse) response; //Perform some preprocessing operations doFilterInternal(httpRequest, httpResponse, filterChain); //Perform some post-processing operations } protected abstract void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException; //Other methods } public class ConcreteFilter extends OncePerRequestFilter { @Override protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException { //Specific filtering logic //Calling methods of parent classes for filtering super.doFilterInternal(request, response, filterChain); //Other post-processing operations } } //Other specific filter classes that implement the Filter interface Summary: The decorator pattern has been widely applied in the implementation of Filter in the Spring framework. By using the decorator mode, Filter can enhance its functionality in a flexible way. Specifically, the abstract class OncePerRequestFilter serves as an abstract decorator, defining a universal filtering process, while the concrete decorator ConcreteFilter inherits from the abstract decorator, implementing specific filtering logic and enhancement functions. This design allows for flexible extension of Filter's functionality while maintaining high cohesion and low coupling of the code.