HOW-TO Use Virtualizers

Report Virtualization is a mechanism JasperReport introduced in order to make possible huge report generation Through different strategies (GZip compression in memory, using a file swap, etc.) they save a lot of memory.

Virtualizers a used exclusively by JasperReports at report fill time, we'll just briefly show here how to use them.

Actually there are 3 implementations:

  • JRSwapFileVirtualizer: A virtualizer that uses a single swap file to serialize virtual data.
  • JRGzipVirtualizer: GZips the pages that it doesn't need, but keeps them in memory.
  • JRFileVirtualizer: Virtualizes data to the filesystem. When this object is finalized, it removes the swap files it makes. The virtualized objects have references to this object, so finalization does not occur until this object and the objects using it are only weakly referenced.

Using the virtualizer

// creating the virtualizer 
JRFileVirtualizer virtualizer = new JRFileVirtualizer(5, "tempFolderPath"); 

// Pass virtualizer object throw parameter map 
parameters.put(JRParameter.REPORT_VIRTUALIZER, virtualizer); 

//Use any call of DynamicJasperHelper where the parameters map is passed
JasperPrint jp = DynamicJasperHelper.generateJasperPrint(dynamicReport, new ClassicLayoutManager(), conn, parametersMap);