For JasperReports 7.0.1+ it's now ((net.sf.jasperreports.json.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource() not ((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource()
((net.sf.jasperreports.json.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource()
((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource()