Holger Brade

Congrat

Congrats

Hello Vaibhav,

there is a link for this question: links

I read the Head First Book and I like the style of this series. For training the questions I also use the SCWCD Book from David Bridgewater (publisher Mac Graw Hill), this book is very good too.

Greetings

Holger

Thank you very much Ankit.

In the book they always separate response and request filter. At the end the solution was quite simple.

Hallo Avi,

I checked chapter 12 but I could not find the quiz. On which page are you?

Holger

ok I understand it. Code concerning the request has to be before chain.doFilter() and code for the response after the method.
The response must be wrapped in this case. The example would be the following:
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException { HttpServletRequest httpRequest = (HttpServletRequest) request; // process request ServletContext ctx = fc.getServletContext(); ctx.log(httpRequest.getMethod() + ' ' + httpRequest.getContextPath() + ' ' + httpRequest.getProtocol()); Enumeration<String> reqHeaders = httpRequest.getHeaderNames(); while (reqHeaders.hasMoreElements()) { String hKey = reqHeaders.nextElement(); String hValue = httpRequest.getHeader(hKey); ctx.log(hKey + ": " + hValue); } // Wrap response HttpServletResponseWrapper wrapperResponse = new HttpServletResponseWrapper((HttpServletResponse) response); // call the servlet chain.doFilter(request, wrapperResponse); // process response ctx.log(""+wrapperResponse.getStatus()); Iterator<String> respHeaders = wrapperResponse.getHeaderNames().iterator(); while (respHeaders.hasNext()) { String hKey = respHeaders.next(); String hValue = wrapperResponse.getHeader(hKey); ctx.log(hKey + ": " + hValue); } }

Thanks

Thanks Ankit.

so far I understand it does not matter where I put the method.
But can you give me an example where a filter can be used as request and response filter?

For me the question in the book suggest that I can write a filter and it can be used as request and
response filter.

I made as an example a filter which outputs the http request and the response header (I know it is not
such a good example, because you have to differ between Request and Response Object, but I can only
imagine examples where I get always two different filter classes) . To output
both headers, I need two classes one for the request and one for the response header.

The request filter:
package com.example; import java.io.IOException; import java.util.Enumeration; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; public class RequestFilter implements Filter { private FilterConfig fc; public void init(FilterConfig config) { fc = config; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException { HttpServletRequest httpRequest = (HttpServletRequest) request; ServletContext ctx = fc.getServletContext(); ctx.log(httpRequest.getMethod() + ' ' + httpRequest.getContextPath() + ' ' + httpRequest.getProtocol()); Enumeration<String> headers = httpRequest.getHeaderNames(); while (headers.hasMoreElements()) { String hKey = headers.nextElement(); String hValue = httpRequest.getHeader(hKey); ctx.log(hKey + ": " + hValue); } chain.doFilter(request, response); } public void destroy() { } }
and the response filter:
package com.example; import java.io.IOException; import java.util.Iterator; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpServletResponseWrapper; public class ResponseFilter implements Filter { private FilterConfig fc; public void init(FilterConfig config) { fc = config; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException { HttpServletResponseWrapper wrapperResponse = new HttpServletResponseWrapper((HttpServletResponse) response); chain.doFilter(request, wrapperResponse); ServletContext ctx = fc.getServletContext(); ctx.log(""+wrapperResponse.getStatus()); Iterator<String> headers = wrapperResponse.getHeaderNames().iterator(); while (headers.hasNext()) { String hKey = headers.next(); String hValue = wrapperResponse.getHeader(hKey); ctx.log(hKey + ": " + hValue); } ctx.log("Context-Type: " + wrapperResponse.getContentType()); } public void destroy() { } }
Is it possible for this example (or a similar example) to have only one filter? If not I would answer for the question "A filter can act on only the request or response object, not both." yes and this would be wrong .

Thanks in advance

Holger

Hello Friends,

I am confused with one question in the Head First Book (Servlets and JSP) about Filters (chapter 13 page 728).
"A filter can act on only the request or response object, not both." This question is not true.

Technically the answer is correct, it will compile and "work", but I can not imagine any case where the request and the
response filter will be the same class or can you give me an example?

The main different between request and response filter are the method call chain.doFilter(request, response).
The request filter calls the chain at the beginning and the response at the end within the doFilter method. Furthermore
the response filter uses a wrapped response object, otherwise we will not get the response back. So it depends
on the kind of filter how I will implement the filter class.

Thanks in advance

Holger