Forces the request encoding to UTF-8 or another configurable character encoding.

Problem: in servlet 2.3, when {@link ServletResponse#setLocale(java.util.Locale)} is called, the character encoding is changed implicit in an unspecified way. To prevent this, this wrapper does not forward the setLocale call. All JSTL fmt:xxx actions call setLocale on the response, which causes the problem.

This package uses a response wrapper that does not allow the character encoding to be changed. Also the filter sets the Request encoding to UTF-8 (or another configurable charset) because most browsers dont follow the http spec and do not send a content-type header when submitting a form. They use the character encoding of the page that contained the form.

The encoding is configurable as filter init parameter `encoding`, via the property `tbeller.charset`. If the filter is installed, it defaults to UTF-8, otherwise it defaults to ISO-8859-1.

The filter automatically changes (or adds) the response encoding of one configurable content-type. If the filter init-param `contentType` is set to `text/html`, then a response content type will of "text/html; charset=iso-8859-1" will be changed into "text/html; charset=utf-8".

The ContentTypeTag sets the content-type and character encoding of the response to the given type.

Filter example:

      <filter>
        <filter-name>CharsetFilter</filter-name>
        <filter-class>com.tonbeller.wcf.charset.CharsetFilter</filter-class>
        <init-param>
          <param-name>encoding</param-name>
          <param-value>ISO-8859-2</param-value>
          <description>character encoding that this filter will enforce</description>
        </init-param>
        <init-param>
          <param-name>contentType</param-name>
          <param-value>text/html</param-value>
          <description>this content type will be set to the above encoding automatically, e.g. "text/html; charset=iso-8859-1" will become "text/html; charset=utf-8"</description>
        </init-param>
      </filter>

see JSTL spec, section 8.4 and fmt:requestEncoding @see ServletResponse#setLocale(java.util.Locale) @see com.tonbeller.tbutils.res