jasperreport生成pdf_jasperreport 导出excel_jasperreport json(25)

summary section always starts a new page if it does not fit on the remaining space of the last page or if

the report has more than one column and on the last page it has already started a second column.

If the main report sections that we have seen here are not sufficient for what you need, maybe you

should consider introducing supplementary sections like group headers and group footers.

We are now going to see how to group data on the report.

6.2 Data Grouping

Groups represent a flexible way to organize data on a report. A report group is represented by sequence

of consecutive records in the data source that have something in common, like the value of a certain

report field for example.

A report group has 3 components:

_ group expression;

_ group header section;

_ group footer section.

The value of the associated group expression is what makes group records stick tighter. This value is

the thing that they have in common. When the value of the group expression changes during the

iteration through the data source at report filling time, a group rupture occurs and the corresponding

group sections <groupFooter> and <groupHeader> are inserted in the resulting document.

We can have as many groups as we want on a report. The order of groups declared in a report design is

important because groups contain each other. One group contains the following group and so on. And

when a larger group encounters a rupture, all subsequent groups are reinitialized.

Data grouping works as expected only when the records in the data source are already

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