Catálogo de publicaciones - libros

This chapter is for those who have never used JasperReports. If you have already installed JasperReports and used the samples, skip to Chapter 2.

Report templates are standard in reporting applications. They define the layout of the documents that the report-filling process produces.

The report-filling process is the most important piece of JasperReports library functionality, because it manipulates sets of data to produce high-quality documents. This is the main purpose of any reporting tool.

The output of the report-filling process is a pixel-perfect document made of multiple pages, each containing a series of absolutely positioned and sized visual elements. The document is an instance of the net.sf.jasperreports.engine.JasperPrint class, and it is the responsibility of the parent application to make use of it once generated by JasperReports.

When filling report templates with data, the engine takes a JasperReport object along with the supplied parameters and data source and generates an in-memory JasperPrint object. If very large datasets are used for report filling, the size of the resulting JasperPrint object could also be very large and might cause the JVM to run out of memory.

Usually you will work only with a few JasperReports library classes and won’t have to get to know the entire API.

Generally speaking, a report template contains all the information about the structure and the aspects of the documents that will be generated when the data is provided. This information determines the position and content of various text or graphic elements that will appear in the document, their appearance, the custom calculations, the data grouping and data manipulation that should be performed when the documents are generated, and so on.

In Chapter 3, we mentioned that there are three entities that must be supplied as input to the report-filling process: the report template, the parameter values, and the data source of the report.

JasperReports works with templates that are structured into multiple sections, like any traditional reporting tool. At report-filling time, the engine iterates through the virtual records of the supplied report data source and renders each report section when appropriate, depending on each section’s defined behavior.

The reports you generate will be empty if you do not put some report elements in the report template. Report elements are displayable objects like static texts, text fields, images, lines, and rectangles that you put in your report template sections. Report elements come in two flavors: Text elements : Static texts and text fields that display dynamic content Graphic elements : Lines, rectangles, ellipses, images, and charts