can't draw the grouped value above stacked bar plot in ggplot2 - r

Question

I have a ggplot2 question, I run the code below show the stacked barplot without add value above each bar correctly:
p=ggplot(data=essnn)
p+geom_bar(binwidth=0.5,stat="identity")+ #
aes(x=reorder(classname,-amount,sum), y=amount, label=amount, fill = sort(year))+
theme()
I want add the sum amount grouped by year in each class, and here is my code:
+geom_text(aes(x=classes,y=total,label=total), data=essnnta, fill=NULL, size=3)
But an error message appear:
Error in fill = year, can not find object "year"
That's my problem: why the object "year" can be found when I draw stack bar plot without add the sum amount grouped by year in each class, but when I add the sum amount grouped by year, the error appear?
> str(essnn)
'data.frame': 48619 obs. of 15 variables:
$ id : int 2006051337 2006051337 2006051337 2006051337 2006051337 2006051337 2004070648 2006031360 2006031360 2004070062 ...
$ gender : Factor w/ 3 levels "","F","M": 3 3 3 3 3 3 3 3 3 3 ...
$ age : num 30 30 30 30 30 30 38 43 43 37 ...
$ class : Factor w/ 92 levels "100ab","100aa",..: 18 18 18 18 18 18 18 18 18 18 ...
$ classname: Factor w/ 1136 levels "cad"," Office2010",..: 111 111 111 111 111 111 116 107 107 107 ...
$ grade : num 7 5 6 8 3 4 1 4 3 2 ...
$ year : Factor w/ 6 levels "98","99","100",..: 3 3 3 3 2 2 4 5 5 3 ...
$ ses : num 212 210 211 213 207 208 217 221 220 210 ...
$ date : int 1010421 1001115 1010214 1010701 1000411 1000627 1020424 1030304 1021121 1001108 ...
$ money : num 5800 5800 5800 5800 5200 5200 3000 0 5500 5500 ...
$ discount : num 1160 1160 1160 1160 1040 1040 600 0 275 550 ...
$ amount : num 4640 4640 4640 4640 4160 ...
$ idc : Factor w/ 7 levels "在校生","校友",..: 2 2 2 2 2 2 2 7 7 7 ...
$ mdy : Date, format: "2012-04-21" "2011-11-15" "2012-02-14" "2012-07-01" ...
$ day : num 1123 1281 1190 1052 1499 ...
> str(essnnta)
'data.frame': 10 obs. of 2 variables:
$ classes: Factor w/ 10 levels "JD","JF",..: 1 7 8 4 6 10 3 5 2 9
$ total : num 55603526 43708950 43555010 35649129 33214372 ...

Answer 1

Your problem might be that your x-axes are not the same in the two data frames. So ggplot does not know which value corresponds with which stack. I am not sure about this as I don't understand the way you define your x axis in the original barplot. I also find it a bit strange to define the aes outside of the ggplot function or the geom_bar. But that might just be me be used to a different kind of syntax.
All in all I find it difficult to help you as you do not provide any reproducible example.

Answer 2

Here is a small bit of data, and a plot that sort of works. If you supplement your question with your data (or a subset of it), see if this works. You may also want to position the label at the top of each bar.
essnn <- data.frame(year = c(98,99,100,101,102),
classname = c("a", "b", "c", "d", "e"),
amount = c(1e6, 2e6,3e6,4e6,5e6))
essnnta <- data.frame(total = c(10, 20, 30, 40, 50))
ggplot(data=essnn, aes(x=reorder(classname,-amount, sum), y=amount, fill = year)) +
geom_bar(binwidth=0.5, stat="identity", position = "stack") +
geom_text(aes(x=essnn$classname, y=essnnta$total, label=essnnta$total), size=3) # not "classes"