Solve Chinese garbled characters in ajax.net 1.0!

When using ajax.netWhen the requestencoding code is gb2312 during updatepanel, garbled characters appear. IfThe simplest way to solve this problem is to use UTF-8. But what should I do if I can't change it to UTF-8 now when I used gb2312?
I originally wanted to do this:

Byte [] buffer = system. Text. encoding. Default. getbytes (tbxremark. Text );
String remark = system. Text. encoding. utf8.getstring (buffer );
Tbxremark. Text = remark;
Order. remark = remark;

But the last word in the result is always garbled, so there is no way to do this:

String S = system. Text. encoding. utf8.getstring (request. binaryread (request. contentlength ));
Namevaluecollection form = httputility. parsequerystring (s );

Tbxremark. Text = form [tbxremark. uniqueid];
Order. remark = tbxremark. text;

I want to write it here!