How may I add two or more rows to vaadin-table footer? And how may I merge two column name, for example I want create column name Person Info which have 3 columns: first name, last name, birthday.
I think the normal vaadin table does not support this out of the box. In later vaadin 7 versions and vaadin 8 there is the Grid component that allows to do exactly this - https://vaadin.com/docs/-/part/framework/components/components-grid.html
If you want to use the table component you could take a look at the https://vaadin.com/directory#!addon/filteringtable source code which seems to do something similar.
Other than that, you could disable the table headers and just add regular components above and below and style them like the table header, but that would probably only work if the column widths are fixed.