Thanks a lot for the example, Gregor. The filter I am working on needs to
change the content of response, so I think I need to write customized
ServletResponseWrapper and ServletOutputStream. And this is where I
encountered the problem, the customized filter I wrote does not behavior as
it says on those websites where I found examples. I am not sure whether or
not Tomcat has its own way to implement Servlet Spec.
-Ben
On Mon, Mar 9, 2009 at 1:56 PM, Gregor Schneider <rc4...@googlemail.com>wrote:
> To give you a start, a small real-world-example:
>
> package com.cr.manuals.filter;
>
> import java.text.SimpleDateFormat;
> import java.util.Calendar;
> import java.util.Date;
> import java.util.Locale;
>
> import javax.servlet.FilterChain;
> import javax.servlet.FilterConfig;
> import javax.servlet.ServletException;
> import javax.servlet.ServletRequest;
> import javax.servlet.ServletResponse;
> import javax.servlet.http.Cookie;
> import javax.servlet.http.HttpServletRequest;
> import javax.servlet.http.HttpServletResponse;
>
> /**
> * Servlet implementation class for Servlet: HeaderFilter
> *
> */
> public class HeaderFilter implements javax.servlet.Filter {
>
> private static String PARAM_ADD_TO_CURRENT_MONTH =
> "ADD_TO_CURRENT_MONTH";
> private FilterConfig filterConfig = null;
> private int months2Add = 0;
> /* (non-Java-doc)
> * @see javax.servlet.http.HttpServlet#HttpServlet()
> */
> public HeaderFilter() {
> super();
> }
>
> /**
> * init() : init() method called when the filter is instantiated.
> * This filter is instantiated the first time j_security_check is
> * invoked for the application (When a protected servlet in the
> * application is accessed).
> */
> public void init(FilterConfig aFilterConfig) throws ServletException
> {
> filterConfig = aFilterConfig;
> months2Add =
> Integer.parseInt(filterConfig.getInitParameter(PARAM_ADD_TO_CURRENT_MONTH));
> }
>
> /**
> * destroy() : destroy() method called when the filter is taken
> * out of service.
> */
> public void destroy() {
> filterConfig = null;
> }
>
> /**
> * doFilter() : doFilter() method called before the servlet to
> * which this filteris mapped is invoked. Since this filter is
> * mapped to j_security_check,this method is called before
> * j_security_check action is posted.
> */
> public void doFilter(ServletRequest aRequest, ServletResponse
> aResponse,
> FilterChain chain) throws
> java.io.IOException, ServletException {
>
> //System.out.println ("******** filter *******");
>
> HttpServletRequest request = (HttpServletRequest)aRequest;
> HttpServletResponse response = (HttpServletResponse)aResponse;
> // call next filter in the chain : let j_security_check
> authenticate
> // user
> response.setHeader("Expires",
> createExpiresHeader(months2Add));
> chain.doFilter(request, response);
>
> }
> /**
> * Create a String in the format EEE, d MMM yyyy HH:mm:ss z"
> * Example: Fri, 4 Aug 2006 09:07:44 CEST
> * The value of the init-parama ADD_TO_CURRENT_MONTH is added to the
> * month-field of the current date
> * @return
> */
> private String createExpiresHeader(int someMonths2Add) {
> SimpleDateFormat sdf = new SimpleDateFormat("EEE, d MMM yyyy
> HH:mm:ss z", Locale.US);
> Calendar cal = Calendar.getInstance();
> cal.add(Calendar.MONTH, someMonths2Add);
> long millis = cal.getTimeInMillis();
> Date d = new Date(millis);
> return sdf.format(d);
> }
> }
>
> In your web.xml:
>
> <filter id="Filter_1">
> <filter-name>HeaderFilter</filter-name>
>
> <filter-class>com.cr.manuals.filter.HeaderFilter</filter-class>
> <init-param>
> <param-name>ADD_TO_CURRENT_MONTH</param-name>
> <param-value>1</param-value>
> </init-param>
> </filter>
> <filter-mapping>
> <filter-name>HeaderFilter</filter-name>
> <url-pattern>/*</url-pattern>
> </filter-mapping>
>
> HTH
>
> Gregor
> --
> just because your paranoid, doesn't mean they're not after you...
> gpgp-fp: 79A84FA526807026795E4209D3B3FE028B3170B2
> gpgp-key available @ http://pgpkeys.pca.dfn.de:11371
>
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