在javaweb中，java类定义的JSON，用response发送到前台页面，如何使用ajax来接收，求解

$.post("./XXXX.do",{"userID":$("#usname").val(),"certCode":$("#certCode").val(),"mobileNo":$("#mobileNo").val(),"validCode":$("#check_code").val(),"findType":findType},function(json){
eval("var obj=" + json);
if (obj.status == "fail"){
if(obj.msg=="timeOut"){
window.location = "./sysErrorMobileAndPc.do?appId=&subAppId=01¶type=&isln=";
}else{
showError(obj.msg,"error_msg","showError","");
}
restoreProc();
checkFormReturn($("#usname").val(),$("#check_code").val());
} e

$.ajax({
type : "POST",
url : url,
data : param,
dataType : "json",
success : function(data) {
if (data.code == 0) {
alert('成功');
} else {
alert('失败');
}
}
});