jasper report table show previous page total - jasper-reports

Question

I am using Jaspersoft® Studio 6.8.0.
I want to have a table which can show previous page total, take following table for example, assume this
table has 3 pages:
grade
10
20
sub total 30
page 1
grade
previous page total 30
40
50
sub total 90
page 2
grade
previous page total 90
60
70
sub total 130
page 3
that is show previous page total from 2nd page to last page.
How to achieve that? thanks!

Answer 1

One way to do it is to create a variable that holds a mutable value set as a side effect by an expression of the text that displays the total on the previous page.
E.g. something like this:
<variable name="TotalVariable" class="java.lang.Integer" calculation="Sum" resetType="Page">
<variableExpression>$F{Column}</variableExpression>
</variable>
<variable name="PreviousTotalHolder" class="java.util.concurrent.atomic.AtomicInteger" calculation="System">
<initialValueExpression>new java.util.concurrent.atomic.AtomicInteger()</initialValueExpression>
</variable>
...display the previous total in the new page
<textField>
<reportElement .../>
<textFieldExpression>"Previous total " + $V{PreviousTotalHolder}.get()</textFieldExpression>
</textField>
...use a dummy property in the page footer to set the total into the holder object
<textField>
<reportElement x="0" y="0" width="90" height="15" uuid="a1ab288e-ae4b-4f12-83a5-e30486bb30d5">
<propertyExpression name="foo">Integer.toString($V{PreviousTotalHolder}.getAndSet($V{TotalVariable}))</propertyExpression>
</reportElement>
<textFieldExpression>"Total " + $V{TotalVariable}</textFieldExpression>
</textField>
There might be other ways to do it depending on the exact design of you report (for instance depending on whether you have a table component or a tabular band report).