异步校验用户名是否重复

JS中：

function checkYhm(obj){
	 var cs = "yhm="+obj.value;
  	 cs = encodeURI(cs);
  	 cs = encodeURI(cs);
         var request = new $WebRequest("../zjxxgl/CheckZjxxYhmServlet",cs,function(result){
	 	if(result != "true"){
			document.getElementById("div_yhm").innerHTML ="此用户名已被注册";
			document.getElementById("div_yhm").style.color = "red";
		 }else{
			document.getElementById("div_yhm").innerHTML ="此用户名可用";
			document.getElementById("div_yhm").style.color = "green";
		 }								
	 });
	 request.Start();
}

页面中：

<td>
  <input type="text" size="30"  class="input1" 
        name="yhm" id="yhm" value="<%=toEmpty(entity.getYhm()) %>"     
        onchange="checkYhm(this);">
  <div id="div_yhm" class="div"></div>
</td>

Servlet中：

String yhm = ParamUtil.getParameter(request,"yhm");
String zjbh = request.getSession().getAttribute("pbzjbh").toString();
IZjxxDAO dao = DAOFactory.getInstance().getZjxxDAO();
if(dao.getAllZjByCondition(" and yhm = '"+yhm+"' and bh not like '"+zjbh+"'").size()>0){
//查询除过它自己，该用户名是否存在
	out.print("false");
}else{
	out.print("true");
}

public List<Zjxx> getAllZjByCondition(String condition) throws Exception {
		String sql = "select * from Zjxx where 1=1 " +condition + ""; 
		   Zjxx zj = null; 
		   List<Zjxx> list = new ArrayList<Zjxx>();
		   Mysql mysql = new Mysql();
		   try {
		        mysql.prepareStatement(sql);
		        ResultSet resultSet = mysql.executeQuery();
		        while(resultSet.next()){
		           zj = new Zjxx(); 
		           zj.setBh(resultSet.getLong("bh"));
		           zj.setYhm(resultSet.getString("Yhm"));
		           list.add(zj);
		         }
		   }catch (SQLException e) {
		      e.printStackTrace();
		   } finally {
		        mysql.freeResource();
		   }
		     return list;
}