Yes. As you know, content written from the JSP page goes straight to the JspWriter, and hence back to the client.
A simple way to modify the content, is to use a special type of custom tag (called a "body tag") to wrap up the content that you want to filter. For example:
Essentially, the <filter> tag can capture the content generated between inside its body, which can then be manipulated before being properly outputted to the actual JspWriter instance.
The technical details around how all this works aren't that tricky, but there is a fair amount of explanation around it. Rather than summarise it here, for full details with examples including a tag that filters HTML characters on page 163, take a look at
Chapter 6, "Body Tags" (from Professional JSP Tag Libraries) which is free to download in PDF format.
Hope that helps.
Simon
[ July 22, 2002: Message edited by: Simon Brown ]