import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.ServletContext;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import javax.servlet.http.HttpServletRequestWrapper;

public class FailSafeResponseFilter implements Filter  {
    FilterConfig filterConfig;
    ServletContext servletContext;
    String contextPath;

    @Override
    public void init(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
        this.servletContext = filterConfig.getServletContext();
        contextPath = servletContext.getContextPath();
    }

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter ( ServletRequest request, ServletResponse response,
                        FilterChain chain ) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;

        chain.doFilter( new FailSafeRequestWrapper(httpRequest), 
                new FailSafeResponseWrapper(httpResponse) );
    }

}

class FailSafeRequestWrapper extends HttpServletRequestWrapper  {
    HttpServletRequest request;
    String contextPath;
    String serverName;

    public FailSafeRequestWrapper(HttpServletRequest request) {
        super(request);
        this.request = request;
        this.contextPath = request.getContextPath();
        this.serverName = request.getServerName();
System.out.println(this + " wrapping " + request);
    }
    
    @Override
    public String getContextPath() {
        String result = contextPath;
        try {
            result = request.getContextPath();
        } catch (Exception e)  {
System.out.println(e);
        }
System.out.println("FailSafe getContextPath " + result);
        return result;
    }

    @Override
    public String getServerName() {
        String result = serverName;
        try {
            result = request.getServerName();
        } catch (Exception e)  {
System.out.println(e);
        }
System.out.println("FailSafe getServerName " + result);
        return result;
    }
}

class FailSafeResponseWrapper extends HttpServletResponseWrapper  {
    HttpServletResponse response;

    public FailSafeResponseWrapper(HttpServletResponse response) {
        super(response);
        this.response = response;
System.out.println(this + " wrapping " + response);
    }

    @Override
    public String encodeRedirectUrl(String url) {
        String result = url;
        try {
            result = response.encodeRedirectURL(url);
        } catch (Exception e)  {
System.out.println(e);
        }
        return result;
    }

    @Override
    public String encodeUrl(String url) {
        String result = url;
        try {
            result = response.encodeURL(url);
        } catch (Exception e)  {
System.out.println(e);
        }
        return result;
    }

    @Override
    public String encodeRedirectURL(String url) {
System.out.println("FailSafe encodeRedirectURL " + url);
        String result = url;
        try {
            result = response.encodeRedirectURL(url);
        } catch (Exception e)  {
System.out.println(e);
        }
        return result;
    }

    @Override
    public String encodeURL(String url) {
System.out.println("FailSafe encodeURL " + url);
        String result = url;
        try {
            result = response.encodeURL(url);
        } catch (Exception e)  {
System.out.println(e);
        }
        return result;
    }

}