$("#activity_project").change(function(){
        var pro=$("#activity_project").val();
     $.ajax({
         type: "POST",
         url: "${pageContext.request.contextPath}/getMyPlan",
         data: { //发送给数据库的数据
             idKey:pro
             },
         dataType: 'json',
         success: function(data) {
                 alert(data);
              $.each(data, function(index,value){
                  alert(data[index].id);

$("#activity_project").append('<option value="data[index].id">data[index].specification</option>');              });
             }
  })
     })