Package net.sf.jasperreports.components.subreport
The Table Component
The majority of reports created by a reporting tool have a tabular structure because, most of the time, the tool has to iterate through a set of records, extracting values from the same fields in each record, then display the values one beside the other, resulting in the table-structured content. You could always design the tables' presentation in JasperReports. However, it did not produce a fully developed table. Text fields and other elements were simply aligned across the different report bands. When they were filled with data at runtime, the output looked like a table even though there is no tabular structure at design time.In order to obtain truly dynamic table structures, the reporting engine was extended by introducing the Table component inside report templates. The Table component advances JasperReport's capabilities a few steps when compared to the List component.
Just like the List component, the Table component iterates through the records of a dataset. But for each of these records, it renders a different cell for each of its declared columns (not just one cell per record, as the List component does). From this perspective, the List component is like a table with only one column. Furthermore, the Table component allows defining cells for column headers and row headers and also has the concept of grouping, just like a normal report template has. Viewed in this way, the Table component is as powerful as a subreport; its content is structured in columns and cells, and its definition is embedded in the containing report template instead of being a separate file altogether.
The Table component gets its data from a subdataset defined in the report. The
component includes a <datasetRun> JRXML element (equivalent to a
JRDatasetRun at the API level),
which contains the information required to instantiate the subdataset. A data source
object can be sent to the subdataset, or, when the subdataset embeds a query, connection
parameters and query parameters can be sent. The subdataset is instantiated when the
Table component is evaluated and it iterates through the records it produces.
From a high-level perspective, a Table component is a list of columns. These columns can be grouped and can form a hierarchy, with adjacent columns sharing a common header and/or footer. When the table is generated at runtime, columns can be skipped/hidden based on a Boolean condition that can be associated with each column.
Within a column, the Table component declares sections for grouping the content, such as a table header and footer, column and row header and footer, and an unlimited number of nested group headers and footers. For each section, the column can specify a cell. Overall, the output of the table is made up of a series of cells that correspond to the content of the table, including, for instance, cells for column and row headers and footers, and headings and summaries for the different levels of groups in the table. The table cells behave much like frame elements, because they can contain several nested elements in a free-form layout.
Each table cell is evaluated in the context of the subdataset, therefore expressions used by the elements can only refer to parameters, fields and variables that are defined in the table's associated subdataset. However, unlike the List component, delayed evaluation times do work for elements in the table cells, with respect to the context of the table dataset.