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webapps/servlets-examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java
webapps/jsp-examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java

6.x, 7.x::

webapps/examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java

5.5.36+, 6.0.36+, 7.0.20+, 8.x::
Since 7.0.20 the filter became first-class citizen and was moved from the examples into core Tomcat and is available to any web application without the need to compile and bundle it separately. See documentation for the list of filters provided by Tomcat. The class name is:

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It was also ported to older Tomcat versions and is available there starting with versions 5.5.36 and 6.0.36. (not yet released at the time of this writing)

Note: The request encoding setting is effective only if it is done earlier than parameters are parsed. Once parsing happens, there is no way back. Parameters parsing is triggered by the first method that asks for parameter name or value. Make sure that the filter is positioned before any other filters that ask for request parameters. The positioning depends on the order of filter-mapping declarations in the WEB-INF/web.xml file, though since Servlet 3.0 specification there are additional options to control the order. To check the actual order you can throw an Exception from your page and check its stack trace for filter names.

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