XSS prevention in JSP/Servlet web application

Question

How can I prevent XSS attacks in a JSP/Servlet web application?

Answer 1

If you want to automatically escape all JSP variables without having to explicitly wrap each variable, you can use an EL resolver as detailed here with full source and an example (JSP 2.0 or newer), and discussed in more detail here:

For example, by using the above mentioned EL resolver, your JSP code will remain like so, but each variable will be automatically escaped by the resolver

...

  
${item.name}
  
${item.price}
  
${item.description}

...

If you want to force escaping by default in Spring, you could consider this as well, but it doesn't escape EL expressions, just tag output, I think:

http://forum.springsource.org/showthread.php?61418-Spring-cross-site-scripting&p=205646#post205646

Note: Another approach to EL escaping that uses XSL transformations to preprocess JSP files can be found here:

http://therning.org/niklas/2007/09/preprocessing-jsp-files-to-automatically-escape-el-expressions/