INTERACTIVE WEB SERVICES WITH JAVA

Filters

- inserting hooks before and after requests are processed
- wrappers modify the request and the response

A Filter can modify

the incoming request, e.g.
- redirect
- check security requirements
- perform logging
the outgoing response, e.g.
- data compression or encryption
- XSLT transformation
- perform logging

FilterChain: multiple filters are processed in deployment order in a stack discipline with the Servlet in the bottom.

Supplementary, HttpServletRequestWrapper and HttpServletResponseWrapper provide wrappers to modify the request/response.

Example filter and deployment declaration:
public class TraceFilter implements Filter { private ServletContext context; public void init(FilterConfig config) throws ServletException { context = config.getServletContext(); } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { context.log("["+request.getRemoteHost()+"] request: "+ ((HttpServletRequest) request).getRequestURL()); chain.doFilter(request, response); context.log("["+request.getRemoteHost()+"] done"); } }

<filter> <filter-name>myfilter</filter-name> <filter-class>TraceFilter</filter-class> </filter> <filter-mapping> <filter-name>myfilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>