Jasper subreport not showing - jasper-reports

Question

I am using Eclipse JasperReports Studio and have run into a problem I can't resolve. I have a pretty basic report with detail fields which return about 30 rows. I have a subreport I want to incorporated into the main report but when I add it nothing displays. I have tried adding it to the Column Footer, in the Page Footer with my Page x of x fields, and in the detail field. Which didn't work so well since it added a blank spot between every row retrieved. I have other reports with sub-reports in various bands and they all work fine. Here is the subreport code for the col footer:
<columnFooter>
<band height="110">
<subreport>
<reportElement isPrintRepeatedValues="false" x="0" y="10" width="555" height="100" uuid="34205e71-ec6b-422c-aa27-057678430999"/>
<connectionExpression><![CDATA[$P{REPORT_CONNECTION}]]></connectionExpression>
<subreportExpression><![CDATA["The_Report.jasper"]]></subreportExpression>
</subreport>
</band>
</columnFooter>
Any obvious reasons why this won't show up? I don't get any errors and the main report runs fine. The subreport works fine on it's own and it is in the same directory as the main report. I compiled it there and the .jasper file is there as well.

Answer 1

I came across the same problem when using subreports.
In the editor: deleting the content form connectionExpression
And putting $P{REPORT_PARAMETERS_MAP} in the Parameters Map Expression did the trick for me.
Source code: <parametersMapExpression><![CDATA[$P{REPORT_PARAMETERS_MAP}]]></parametersMapExpression>

Answer 2

Verify that the Subreport Expression is pointing to the correct/expected subreport. There are times (often due to copying and/or hand-editing existing JRXML files) where the Subreport Expression is still pointing to the subreport Jasper file of the original, Main report. I just ran into this case, myself.
Make sure that
<subreportExpression><![CDATA["The_Report.jasper"]]></subreportExpression>
isn't supposed to be something like
<subreportExpression><![CDATA["The_New_SubReport.jasper"]]></subreportExpression>
or contain the Subreport directory like
<subreportExpression><![CDATA[$P{SUBREPORT_DIR} + "The_New_SubReport.jasper"]]></subreportExpression>
You should also verify that your subreport doesn't require data in order to display. If it does and your query doesn't return any data, you can do the following:
SELECT FIELD_NAME
FROM TABLE
WHERE KEY = $P{KEY}
UNION ALL
SELECT NULL AS FIELD_NAME
FROM DUAL WHERE (
SELECT COUNT(*)
FROM TABLE
WHERE KEY = $P{KEY}
) = 0

Answer 3

A quick reminder, after double checking that you have the correct values for all the <subreportExpression> elements. Make sure you Build All the project files.
The main report will call the compiled version of the subreport. So once you have tested and saved your subreport, click the Build All button or click on the Menu option under the 'Project' menu at the top of the window.