package moreservlets.filters; 

import java.io.*; 
import javax.servlet.*; 
import javax.servlet.http.*; 
import java.util.*; 

/** Filter that replaces all occurrences of a given 
 *  string with a replacement. This is an abstract class: 
 *  you <I>must</I> override the getTargetString and 
 *  getReplacementString methods in a subclass. The 
 *  first of these methods specifies the string in 
 *  the response that should be replaced. The second 
 *  of these specifies the string that should replace 
 *  each occurrence of the target string. 
 */ 

public abstract class ReplaceFilter implements Filter {
  private FilterConfig config; 

  public void doFilter(ServletRequest request, 
                       ServletResponse response, 
                       FilterChain chain) 
      throws ServletException, IOException {
    CharArrayWrapper responseWrapper =
							new CharArrayWrapper((HttpServletResponse)response); 
    // Invoke resource, accumulating output in the wrapper. 
    chain.doFilter(request,responseWrapper); 
    // Turn entire output into one big String. 
    String responseString = responseWrapper.toString(); 
    // In output, replace all occurrences of target string 
    // with replacement string. 
    responseString =
							FilterUtils.replace(responseString,
							getTargetString(),
							getReplacementString()); 
    // Update the Content-Length header. 
    updateHeaders(response, responseString); 
    PrintWriter out = response.getWriter();
							out.write(responseString); 
  } 

  /** Store the FilterConfig object in case subclasses 
   *  want it. 
   */ 

  public void init(FilterConfig config) 
      throws ServletException {
    this.config = config; 
  } 

  protected FilterConfig getFilterConfig() {
    return(config); 
  } 

  public void destroy() {} 

  /** The string that needs replacement. 
   *  Override this method in your subclass. 
   */ 

  public abstract String getTargetString(); 

  /** The string that replaces the target. 
   *  Override this method in your subclass. 
   */ 

  public abstract String getReplacementString(); 
  /** Updates the response headers. This simple version just sets 
   *  the Content-Length header, assuming that we are using a 
   *  character set that uses 1 byte per character. For other 
   *  character sets, override this method to use different logic 
   *  or to give up on persistent HTTP connections. In this latter 
   *  case, have this method set the Connection header to "close". 
   */ 

  public void updateHeaders(ServletResponse response, 
                            String responseString) {
    response.setContentLength(responseString.length()); 
  } 
} 

package moreservlets.filters; 

/** Small utility to assist with response wrappers that 
 *  return strings. 
 */ 

public class FilterUtils {

  /** Change all occurrences of orig in mainString to 
   *  replacement. 
   */ 

  public static String replace(String mainString, 
                               String orig, 
                               String replacement) {
    String result = ""; 
    int oldIndex = 0; 
    int index = 0; 
    int origLength = orig.length(); 
    while((index = mainString.indexOf(orig, oldIndex)) 
          != -1) {
      result = result + 
               mainString.substring(oldIndex, index) + 
               replacement; 
      oldIndex = index + origLength; 
    } 
    result = result + mainString.substring(oldIndex); 
    return(result); 
  } 
} 

package moreservlets.filters; 

public class ReplaceSiteNameFilter extends ReplaceFilter {
  public String getTargetString() {
    return("filtersRus.com"); 
  } 

  public String getReplacementString() {
    return("weBefilters.com"); 
  } 
} 

<?xml version="1.0" encoding="ISO-8859-1"?> 
<!DOCTYPE web-app PUBLIC 
    "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" 
    "http://java.sun.com/dtd/web-app_2_3.dtd"> 
<web-app> 
  <!-- ... --> 

  <!-- Register the name "ReplaceSiteNameFilter" for 
       moreservlets.filters.ReplaceSiteNameFilter. 
  --> 
  <filter> 
    <filter-name>ReplaceSiteNameFilter</filter-name> 
    <filter-class> 
      moreservlets.filters.ReplaceSiteNameFilter 
    </filter-class> 
  </filter> 
  <!-- ... --> 


  <!-- Apply ReplaceSiteNameFilter to page2.jsp page 
       in the plugSite directory 
  --> 
  <filter-mapping> 
    <filter-name>ReplaceSiteNameFilter</filter-name> 
    <url-pattern>/plugSite/page2.jsp</url-pattern> 
  </filter-mapping> 

  <!-- ... --> 
</web-app> 

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> 
<HTML> 
<HEAD> 
<TITLE>filtersRus.com</TITLE> 
<LINK REL=STYLESHEET 
      HREF="../filter-styles.css" 
      TYPE="text/css"> 
</HEAD> 
<BODY> 
<CENTER> 
<TABLE BORDER=5> 
  <TR><TH CLASS="TITLE">filtersRus.com</TABLE> 
<P> 
<TABLE> 
  <TR> 
    <TH><IMG SRC="../images/air-filter.jpg" 
             ALT="Air Filter"> 
    <TH><IMG SRC="../images/coffee-filter.gif" 
             ALT="Coffee Filter"> 
    <TH><IMG SRC="../images/pump-filter.jpg" 
             ALT="Pump Filter"> 
</TABLE> 

<H3>filtersRus.com specializes in the following:</H3> 
<UL> 
  <LI>Air filters 
  <LI>Coffee filters 
  <LI>Pump filters 
  <LI>Camera lens filters 
  <LI>Image filters for Adobe Photoshop 
  <LI>Web content filters 
  <LI>Kalman filters 
  <LI>Servlet and JSP filters 
</UL> 
Check out <A HREF="../TodaysSpecial">Today's Special</A>. 
</CENTER> 
</BODY> 
</HTML>