req.setCharacterEncoding("GBK");
resp.setCharacterEncoding("GBK");

業務程式碼

##############################################

    //自定義返回方式，data業務返回報文，contenttype 決定了亂碼問題

String responseheader = req.getParameter("responseheader");
if(RESPONSE_JSON.equals(responseheader)){
    resp.setContentType("application/json"
 
);
}else{
    resp.setContentType("text/html; charset=gbk");
}

resp.setHeader("Cache-Control", "no-cache");
PrintWriter pw = resp.getWriter();
pw.write(data);
pw.flush();
pw.close();