org.sitemesh.webapp.contentfilter
Class ContentBufferingFilter

java.lang.Object
  org.sitemesh.webapp.contentfilter.ContentBufferingFilter

All Implemented Interfaces:

javax.servlet.Filter

Direct Known Subclasses:

SiteMeshFilter

public abstract class ContentBufferingFilter
extends Object
implements javax.servlet.Filter

Abstract Filter implementation that writes the main content of a response to a temporary buffer where it can then be post-processed before being served.

Subclasses should:

• Pass in a Selector to the constructor: Which provides rules for selecting which requests this filter should be applied to. For a basic implementation, use BasicSelector.
• Implement postProcess(String, CharBuffer, HttpServletRequest, HttpServletResponse, ResponseMetaData): Perform the actual post processing of the content that was buffered.

Example

This primitive example creates a Filter that will intercept responses with a MIME type of text/plain, and replace all occurrences of the word 'sheep' with 'cheese'. Yes, it's pointless, but should illustrate usage.

 public class SheepToCheeseFilter extends ContentBufferingFilter {
   public SheepToCheeseFilter() {
     super(new BasicSelector("text/plain"));
   }
   public boolean postProcess(String contentType, CharBuffer buffer,
                              HttpServletRequest request, HttpServletResponse response) {
     String text = buffer.toString();
     if (!text.contains("sheep")) {
       // If no modification is required, returning false will signal
       // ContentBufferingFilter to write the original buffer back out.
       return false;
     }
     text = text.replaceAll("sheep", "cheese");
     response.getWriter().print(text);
     return true;
   }
 }
 

Author:

Joe Walnes, Scott Farquhar

Constructor Summary

protected

ContentBufferingFilter(Selector selector)

Method Summary

protected void	bufferAndPostProcess(javax.servlet.FilterChain filterChain, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, Selector selector) Apply next filter/servlet to the buffer, post process the response and send to the real response.
void	destroy()
void	doFilter(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse, javax.servlet.FilterChain filterChain)
protected ContainerTweaks	getContainerTweaks()
protected javax.servlet.FilterConfig	getFilterConfig()
void	init(javax.servlet.FilterConfig filterConfig)
protected ContainerTweaks	initContainerTweaks()
protected abstract boolean	postProcess(String contentType, CharBuffer buffer, javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response, ResponseMetaData responseMetaData)
protected javax.servlet.http.HttpServletRequest	wrapRequest(javax.servlet.http.HttpServletRequest request) Override to wrap the HttpServletRequest sent to the end point to be buffered.
protected void	writeOriginal(javax.servlet.http.HttpServletResponse response, CharBuffer buffer, HttpServletResponseBuffer responseBuffer) Write out the original unmodified buffer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ContentBufferingFilter

protected ContentBufferingFilter(Selector selector)

Method Detail

postProcess

protected abstract boolean postProcess(String contentType,
                                       CharBuffer buffer,
                                       javax.servlet.http.HttpServletRequest request,
                                       javax.servlet.http.HttpServletResponse response,
                                       ResponseMetaData responseMetaData)
                                throws IOException,
                                       javax.servlet.ServletException

Returns:

Whether the content was processed. If false, the original content shall be written back out.

Throws:

IOException

javax.servlet.ServletException

init

public void init(javax.servlet.FilterConfig filterConfig)
          throws javax.servlet.ServletException

Specified by:

init in interface javax.servlet.Filter

Throws:

javax.servlet.ServletException

destroy

public void destroy()

Specified by:

destroy in interface javax.servlet.Filter

initContainerTweaks

protected ContainerTweaks initContainerTweaks()

getFilterConfig

protected javax.servlet.FilterConfig getFilterConfig()

getContainerTweaks

protected ContainerTweaks getContainerTweaks()

doFilter

public void doFilter(javax.servlet.ServletRequest servletRequest,
                     javax.servlet.ServletResponse servletResponse,
                     javax.servlet.FilterChain filterChain)
              throws IOException,
                     javax.servlet.ServletException

Specified by:

doFilter in interface javax.servlet.Filter

Throws:

IOException

javax.servlet.ServletException

bufferAndPostProcess

protected void bufferAndPostProcess(javax.servlet.FilterChain filterChain,
                                    javax.servlet.http.HttpServletRequest request,
                                    javax.servlet.http.HttpServletResponse response,
                                    Selector selector)
                             throws IOException,
                                    javax.servlet.ServletException

Apply next filter/servlet to the buffer, post process the response and send to the real response.

Throws:

IOException

javax.servlet.ServletException

writeOriginal

protected void writeOriginal(javax.servlet.http.HttpServletResponse response,
                             CharBuffer buffer,
                             HttpServletResponseBuffer responseBuffer)
                      throws IOException

Write out the original unmodified buffer.

Throws:

IOException

wrapRequest

protected javax.servlet.http.HttpServletRequest wrapRequest(javax.servlet.http.HttpServletRequest request)

Override to wrap the HttpServletRequest sent to the end point to be buffered.