changeanswerfilter.java

icsamples目录中有icsamples网络程序。 这个程序包括J2EE网络层的范例程序

package jwadbook.filter;

import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.RequestDispatcher;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.*;
import java.util.*;

/**
 *
 * @author Jian (James) Cai
 */


public class ChangeAnswerFilter implements Filter
{

    public void init(final FilterConfig filterConfig) 
    {

    }

    public void destroy()
    {

    }
    public ChangeAnswerFilter() {
    }

    public void doFilter(final ServletRequest request,
			 final ServletResponse response,
			 FilterChain chain) 
	throws java.io.IOException, javax.servlet.ServletException 
    {
	Vector emptyprameters = new Vector();
	HttpServletRequest httprequest = (HttpServletRequest)request;
	GenericRequestWrapper wrapper = new GenericRequestWrapper(httprequest);
	Enumeration paramNames = httprequest.getParameterNames();
	while (paramNames.hasMoreElements()) {
	    String paramName = (String)paramNames.nextElement();
	    String[] paramValues = httprequest.getParameterValues(paramName);
	    if(paramName.equals("Comment"))
		{
			    String paramValue = paramValues[0];
			    if ((paramValue.equals("Please Enter Other Information")))
				{
				    wrapper.setParameterValue(paramName, "No Comment Added (from ChangeAnswerFilter)");
				}
			    else
				{
				    wrapper.setParameterValue(paramName, paramValue);
				}
			   
		}
	    else
		{
		    if (paramValues.length== 1)
			{
			    String paramValue = paramValues[0];
			    wrapper.setParameterValue(paramName, paramValue);
			}
		}
       }

	chain.doFilter(wrapper, response);
    }

}