不能访问AJAX输入参数在Action类

$.ajax({

url: "ApplyCouponCode",

type: "POST",

data: {couponCode: $('#PaymentMethod_couponCode').val()},

dataType: "json",

error: function(){

alert('Error');

},

success: function(data){

alert('SUCCESS');

$('#spanValidatedCoupon').text('Is coupon valid? ' data.couponIsValid ' couponAmount = ' data.couponAmount);

}

});

动作类别：

public String applyCouponCode() throws Exception {

if(logger.isDebugEnabled()){

logger.debug("data: couponCode '" couponCode "'");

}

return SUCCESS;

}

Action类方法[applyCouponCode]被调用。couponCode是空的..请指教。 couponCode有公共getter/setter方法..我还需要做什么？