ajax乱码有关问题，100分相送

ajax乱码问题，100分相送。
一：servlet.java文件内容如下：

package   com.lz;

import   java.io.IOException;

import   javax.servlet.ServletException;
import   javax.servlet.http.HttpServlet;
import   javax.servlet.http.HttpServletRequest;
import   javax.servlet.http.HttpServletResponse;


public   class   SelectUser   extends   HttpServlet
{
private   static   final   long   serialVersionUID   =   1L;
public   void   doGet(HttpServletRequest   request,   HttpServletResponse   response)   throws   ServletException,   IOException
{
doPost(request,   response);
}
public   void   doPost(HttpServletRequest   request,   HttpServletResponse   response)   throws   ServletException,   IOException
{   //   生成一个随机数
//response.setHeader( "Content-Type ",   "text/html;charset=utf-8 ");  

                StringBuffer   sb   =   new   StringBuffer();
                sb.append( " <?xml   version= '1.0 '   encoding= 'utf-8 '?> ");
//   将生成的随机数通过response对象写到客户端去，客户端接收将值写页面的recieveValue中。在这里就可以查询数据库，将查询的结果返回
String   a   = "select   *   from   user   where   name= ' "+request.getParameter( "name ")+ " '   and   mobile= ' "+request.getParameter( "mobile ")+ " ' "   ;
System.out.println(a);


try   {
DB   db=new   DB();
java.sql.ResultSet   rs   =   db.executeQuery(a);
sb.append( " <message> ");
while(rs.next()){
sb.append( " <info> "+rs.getString( "address ")+ " </info> ");
sb.append( " <info> "+rs.getString( "postalcode ")+ " </info> ");
sb.append( " <info> "+rs.getString( "phone ")+ " </info> ");
sb.append( " <info> "+rs.getString( "phone1 ")+ " </info> ");
sb.append( " <info> "+rs.getString( "phone2 ")+ " </info> ");
sb.append( " <info> "+rs.getString( "email ")+ " </info> ");
}
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " <info> "+ "   "+ " </info> ");
sb.append( " </message> ");

db.close();
}   catch   (Exception   e)   {
//   TODO   Auto-generated   catch   block
e.printStackTrace();
}
//response.setContentType( "text/html;charset=gb2312 ");
//response.setCharacterEncoding( "utf-8 ");

response.setContentType( "text/html;   charset=utf-8 ");
response.setHeader( "Cache-Control ", "no-cache ");
response.getWriter().write(sb.toString());

response.getWriter().flush();