walters 
Walters is a fast HTML (and href, uri, xml, javascript) escaping library for JRuby.
It is optimised for the non-escaping case - i.e. where the input string contains no characters requiring escaping.
Example usage
jruby-1.7.4.dev :001 > require 'walters'
=> true
jruby-1.7.4.dev :002 > Walters.escape_html('<html>')
=> "<html>"
The same extension can also be used from the legacy CRuby VM for compatibility.
2.0.0p0 :001 > require 'walters'
=> true
2.0.0p0 :002 > Walters.escape_html('<html>')
=> "<html>"
Benchmarks
Escaping 1000 bytes of text requiring escaping 1000000 times under jruby-1.7.4:
user system total real
Rack::Utils.escape_html 89.980000 0.230000 90.210000 ( 90.272000)
Haml::Helpers.html_escape 50.420000 0.170000 50.590000 ( 51.147000)
ERB::Util.html_escape 44.650000 0.130000 44.780000 ( 45.518000)
CGI.escapeHTML 36.230000 0.090000 36.320000 ( 36.358000)
String#gsub 35.490000 0.090000 35.580000 ( 35.587000)
Walters.escape_html 10.090000 0.030000 10.120000 ( 10.126000)
Escaping 1000 bytes of html-free text 1000000 times under jruby-1.7.4:
user system total real
Rack::Utils.escape_html 3.530000 0.010000 3.540000 ( 3.601000)
Haml::Helpers.html_escape 4.140000 0.010000 4.150000 ( 4.196000)
ERB::Util.html_escape 11.710000 0.030000 11.740000 ( 11.876000)
CGI.escapeHTML 3.440000 0.010000 3.450000 ( 3.548000)
String#gsub 3.470000 0.000000 3.470000 ( 3.531000)
Walters.escape_html 0.660000 0.010000 0.670000 ( 0.663000)
Punching ducks
There are monkey-patching shims supplied that replace common html escaping functions with calls to the Walters escape_html function.
e.g. to patch Rack::Utils.escape_html to use Walters.escape_html:
require 'walters/html/rack'
Credits
The escaping routines are based on C code from the Houdini project, and the specs, benchmarks and monkey patches come from the escape_utils project