jquery.ajax

 var params = {};//定义一个数组
    var USERNAME= $("#USERNAME").val();
    params["USERNAME"]=USERNAME;
    $.ajax({
         type:"post",
         url:"<%=path%>/memberAction.do?method=checkName",
         data:params, //传递值到后台
         dataType : "text",
         async:true,
         success:function(data){//返回参数
     ///alert(data);
             $("#div1").text(data);
             }
        })

--后台MemberAction.java

//检验用户名是否已注册
private String name;
public ActionForward checkName(ActionMapping mapping, ActionForm form,
        HttpServletRequest request, HttpServletResponse response){
    MemberActionForm maf = (MemberActionForm) form;
    IMemberService memberService= new MemberServiceImpl();
     response.setCharacterEncoding("UTF-8");
        HttpSession session = request.getSession();
        String USERNAME = request.getParameter("USERNAME")+"";
     boolean bl=false;
     System.out.println("要查找的用户名为1： "+USERNAME);
   //  String name=request.getParameter("USERNAME");
     bl=memberService.do_checkname(USERNAME);
    CommUtil cu=new CommUtil();
    if(bl==false)  {
          //request.setAttribute("name", "have");
        cu.outXmlString("该用户名已注册",response);
    }
    else {
        cu.outXmlString("该用户名可用",response);
        //request.setAttribute("name", "ok");
    }
    return null;
}
}

 ---后台MemberServiceImpl.java

 public boolean do_checkname(String name){
     System.out.println("要查找的用户名为2： "+name);//打印获取到的参数
     boolean b1 = false;
     StringBuffer bufSql=new StringBuffer();
     bufSql.append("select USERNAME from IBMS_WEB_REGISTER where USERNAME='"+name+"'");
     ArrayList list = DBTools.doSelect(bufSql.toString());
     if (list.size()>0) {
         b1=false;
     }
     else {
         b1=true;
     }
     System.out.println(b1);
     return b1;
 }

 ---后台，字符流转换

     //字符输出流转换
     public void outXmlString(String str, HttpServletResponse response) {
         response.setContentType("text/html;charset=UTF-8");
         outString(str, response);
     }
     public void outString(String str, HttpServletResponse response) {
         try {
             PrintWriter out = response.getWriter();
             out.write(str);
         } catch (IOException e) {
             e.printStackTrace();
         }
     }