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Subreports are an important feature of a report-generating tool. They enable you to create more complex reports and simplify the design work. Subreports are very useful when creating master-detail reports or when the structure of a single report is not sufficient to describe the complexity of the desired output document.

A dataset is a concept that lies somewhere between a data source and a subreport. Datasets allow the engine to iterate through some virtual records, just as data sources do, but they also enable calculations and data grouping during this iteration using variables and groups. Because dataset declarations contain parameters, fields, variables, and groups, they closely resemble subreports, but they completely lack any visual content (i.e., they have no sections or layout information at the dataset level).

JasperReports now has built-in support for charts using the new chart component, which greatly simplifies the way charts are included inside reports. Previously, users had to completely rely on scriptlets to gather the chart data and render the chart using an image element in the report template.

A crosstab is a special type of report element that summarizes data into a two-dimensional grid. Crosstabs usually display the joint distribution of two or more variables in the form of a table in which both rows and columns are dynamic, and in which the table cells use these variables to display aggregate data such as sums, counts, minimums, and maximums.

All the data displayed in a report comes from the report parameters and report fields. This data can be processed using the report variables and their expressions. Some variables are initialized according to their reset type when the report starts, or when a page or column break is encountered, or when a group changes. Furthermore, variables are evaluated every time new data is fetched from the data source (for every row).

JasperReports lets you associate a java.util.ResourceBundle with the report template, either at design time (by using the new resourceBundle attribute) or at runtime (by providing a value for the built-in REPORT_RESOURCE_BUNDLE parameter).

The proprietary document format used by JasperReports to generate and store final documents is represented by a net.sf.jasperreports.engine.JasperPrint object, which can be serialized for transfer over the network or permanent storage. However, when these documents must be sent to third-party consumers who do not have the proper tools to view and print them in the JasperReports proprietary format, the best solution is to export those documents to more popular formats like PDF, HTML, RTF, XLS, ODT, or CVS, for which there are specialized viewers available on almost all platforms.

The configuration properties of the JasperReports library can be specified using a properties file. The file can be read from the file system, accessed as a resource from the classpath, or loaded from an URL. The default name of the properties file is jasperreports.properties. The net.sf.jasperreports.properties system property can be used to specify a different file name or location. The default or custom name is successively interpreted as a file name, a resource name, and an URL; the properties are read from the first succeeding source.

Previous chapters have presented the core functionality that most people will use when working with the JasperReports library. However, some complex requirements of your specific applications might force you to dig deeper into the JasperReports functionality. The following sections provide a closer look at those aspects that can help you make fuller use of the JasperReports library.