Book Image

JasperReports for Java Developers

Book Image

JasperReports for Java Developers

Overview of this book

JasperReports is the world's most popular embeddable Java open source reporting library, providing Java developers with the power to easily create rich print and web reports. This book shows you exactly how to get started, and develop the skills to get the most from JasperReports. The book steers you through each point of report setup, to creating, designing, formatting, and exporting reports with data from a wide range of datasources, and integrating JasperReports with other Java frameworks. Starting with the basics of adding reporting capabilities to your application, and creating report templates you will first see how to produce your reports through the use of JRXML files, custom ANT targets, and then see preview them in both the browser and the native browser of JasperReports. Getting data into your reports is the next step, and you will see how to get data from a range of datasources, not only databases, but XML files, and Java Objects, among others. You will create better looking reports with formatting and grouping, as well as adding graphical elements to the report. You will export your reports to a range of different formats, including PDF and XML. Creating reports will be made even easier with a walkthrough of the iReport Designer visual designing tool. To round things off, you will see how to integrate your reports with other Java frameworks, using Spring or Hibernate to get data for the report, and Java Server Faces or Struts for presenting the report.
Table of Contents (13 chapters)
12
Index

Handling Very Large Reports

Sometimes, when filling a report, the report datasource may have a lot of data. In some cases, the generated report can become very large, larger than the memory allocated for the JVM, causing an OutOfMemoryException.

It is possible to set up JasperReports so that it stores segments of a report on disk in order to free up some memory. This can be accomplished by using the REPORT_VIRTUALIZER built-in report parameter. The value for this parameter must be an instance of a class implementing net.sf.jasperreports.engine.JRVirtualizer. JasperReports comes with an implementation of this interface, namely net.sf.jasperreports.engine.fill.JRFileVirtualizer. This implementation is sufficient to handle the vast majority of large reports. If for some reason this implementation is not sufficient for our needs, we can always create our own implementation of net.sf.jasperreports.engine.JRVirtualizer. The following example illustrates typical usage of JRVirtualizer.

package...