How to change JRBaseSubreport expression with JasperReports API

Question

I'm using JasperReports API through PHP/Java Bridge. This means that the PHP side is on another machine than the Java side and the two side doesn't share the same filesystem.

To load a report, I must read the .jasper file in PHP and convert it to a java.io.InputStream instance and load it with net.sf.jasperreports.engine.util.JRLoader::loadObject static method.

So everything works fine until my report have subreports referencing a file that the Java side doesn't have access. So my solution was to visit all subreports (using net.sf.jasperreports.engine.util.JRElementsVisitor class), evaluate subreport expression, load the report using the same method as the main report, but it in parameters of the main report.

And then, here is my problem, I don't know how to change the JRBaseSubreport expression to point to the newly added parameter.

So my question is, how to change JRBaseSubreport expression?

Answer 1

I am not sure if this is what you mean or not, but you can actually change the definition in your JRXML for the subreports from using a String to using net.sf.jasperreports.engine.JasperReport

For instance it will usually add the following parameter to your report when you add a subreport:

<parameter name="SUBREPORT_DIR" class="java.lang.String" isForPrompting="false">
    <defaultValueExpression><![CDATA["C:\\reports\\"]]
    </defaultValueExpression>
</parameter>

And for the subreport element itself it will add something like:

<subreport>
  <reportElement uuid="64d21a88-9389-49f5-ba63-1f33aac5a39f" x="821" y="0" width="200" height="100"/>
  <connectionExpression><![CDATA[$P{REPORT_CONNECTION}]]></connectionExpression>
  <subreportExpression><![CDATA[$P{SUBREPORT_DIR} + "report4_subreport1.jasper"]]></subreportExpression>
</subreport>

Instead you of passing int the SUBREPORT_DIR pass in the compiled JasperReport Object. So change your parameter to:

<parameter name="SUBREPORT" class="net.sf.jasperreports.engine.JasperReport" isForPrompting="false"/>

and then the subreport element too:

<subreport>
  <reportElement uuid="64d21a88-9389-49f5-ba63-1f33aac5a39f" x="821" y="0" width="200" height="100"/>
  <connectionExpression><![CDATA[$P{REPORT_CONNECTION}]]></connectionExpression>
  <subreportExpression><![CDATA[$P{SUBREPORT}]]></subreportExpression>
</subreport>

Then it is just a matter of knowing what subreports you need for particular report.

NOTE: This does have the unfortunate side effect of it not running in iReport, but I usually just swap the parameter from a JasperReport to String instance when testing in iReport to get around it.