The Interceptor Pattern

1. The Interceptor Pattern Filters in the Servlet 2.3 Specification Craig E. Ward CMSI 688 Object Technology Fall 2002 Instructor Munir Samplewala

2. Agenda • Description of the Interceptor Pattern • Uses of the Pattern • Code Samples • Software Requirements • Summary and Conclusions • Sources and Resources • Demonstration (if practical) • Questions CMSI 688 Object Technologies

3. UML Class Diagram CMSI 688 Object Technologies

4. UML Sequence Diagram CMSI 688 Object Technologies

5. Flow Diagram CMSI 688 Object Technologies

6. Similar Patterns • Chain of Responsibility • Decorator • Front Controller • Different because… • All Interceptors may act on the request • The other patterns are “built-in” • Interceptor Filters are pluggable CMSI 688 Object Technologies

7. Interceptor Pattern Uses • Authentication • Access Validation • System Logging • System Debugging • Data Encoding • Browser Trapping • Response Filtering CMSI 688 Object Technologies

8. javax.servlet.Filter void init(FilterConfig filterConfig) void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) void destroy() CMSI 688 Object Technologies

9. javax.servlet.FilterChain void doFilter(ServletRequest request, ServletResponse response) CMSI 688 Object Technologies

10. javax.servlet.http Wrappers • javax.servlet.http.HttpServletRequestWrapper • javax.servlet.http.HttpServletResponseWrapper These classes provide a complete set of methods implementing the HttpServletRequest and HttpServletResponse classes. CMSI 688 Object Technologies

11. An Example of doFilter() public void doFilter(ServletRequest srequest, ServletResponse sresponse, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest)srequest; request.setCharacterEncoding(targetEncoding); // move on to the next chain.doFilter(srequest,sresponse); } CMSI 688 Object Technologies

12. Deployment Descriptor • New tags filter and filter-mapping <filter> <filter-name>EncodeFilter</filter-name> <display-name>EncodeFilter</display-name> <description></description> <filter-class>corepatterns.filters.encodefilter.EncodeFilter</filter-class> </filter> <filter-mapping> <filter-name>EncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> CMSI 688 Object Technologies

13. Software Requirements • Servlet container implementing 2.3 • Tomcat 4 • J2EE 1.3 CMSI 688 Object Technologies

14. Summary and Conclusions • Filters are a powerful addition to the Servlet specification • Pluggable wrappers for existing code • Add security • Add debugging • Add Logging • Greater separation of content from technology CMSI 688 Object Technologies

15. Sources and Resources • Sun Microsystems J2EE Blueprints • http://java.sun.com/blueprints/ • http://java.sun.com/blueprints/patterns/InterceptingFilter.html • http://developer.java.sun.com/developer/JDCTechTips/2001/tt0626.html • Li, Sing. Filtering tricks for your Tomcat. • http://www-106.ibm.com/developerworks/library/j-tomcat/index.html • Hunter, Jason, William Crawford. Java Servlet Programming, O’Reilly, 2001. CMSI 688 Object Technologies

16. Demonstration If time is available and the equipment can be setup, the example from “Filtering tricks for your Tomcat” will be demonstrated. CMSI 688 Object Technologies

17. Questions? That’s All Folks! CMSI 688 Object Technologies