this method is really stupid. it shouldn't be there, and you shouldn't use it.
for a body in a POST request, the encoding should have been explicitly defined by the client in the Content-Type header. if not, it's a bad request. 
for a GET request URI, the client cannot specify encoding, and the server must have an implicit encoding, and the programmer needs to set the encoding, yet that method does not exist in Servlet API!
however, you servlet container could have a proprietary way of doing that.
the best way is probably set the default encoding of your JVM to UTF-8.
The "charset" parameter is used with some media types to define the character set (section 3.4) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or its subsets MUST be labeled with an appropriate charset value.