ernst_2's post in Subreport - Close connection was marked as the answer
September 24, 2015
Found it! <parameter name="P_SUB_DATASOURCE" class="com.jaspersoft.jasperserver.api.metadata.jasperreports.domain.JdbcReportDataSource" isForPrompting="false"> <defaultValueExpression><![CDATA[com.jaspersoft.jasperserver.api.engine.jasperreports.util.RepositoryUtil.getThreadRepositoryContext().getRepository().getResource(null,"/<path to data source>/")]]></defaultValueExpression></parameter>[/code]<parameter name="P_SUB_CONNECTION" class="java.sql.Connection" isForPrompting="false"> <defaultValueExpression><![CDATA[java.sql.DriverManager.getConnection($P{P_SUB_DATASOURCE}.getConnectionUrl(),$P{P_SUB_DATASOURCE}.getUsername(),$P{P_SUB_DATASOURCE}.getPassword())]]></defaultValueExpression></parameter> [/code]<subreport> <reportElement mode="Opaque" x="555" y="0" width="5" height="20"/> <subreportParameter name="P_B"> <subreportParameterExpression><![CDATA[$F{user}]]></subreportParameterExpression> </subreportParameter> <connectionExpression><![CDATA[$P{P_SUB_CONNECTION}]]></connectionExpression> <returnValue subreportVariable="V_M" toVariable="V_M"/> <subreportExpression><![CDATA["repo:0001_Subreport.jrxml"]]></subreportExpression></subreport>[/code]<textField> <reportElement x="555" y="10" width="5" height="20"/> <textElement verticalAlignment="Middle"/> <textFieldExpression><![CDATA[""; $P{P_SUB_CONNECTION}.close()]]></textFieldExpression></textField>[/code]