How to get all grid items selected when header is selected(GWT)?

I am working on GWT project, and I have grid with some columns and I set that columns have checkbox option(with columnConfigs.add(selectionModel.getColumn()), but I don't know how to set that when header is selected then all columns in grid also become selected. This is my part of code where I set that columns have checkbox option:

 @Override
    protected List<ColumnConfig> getColumns() {
        List<ColumnConfig> columnConfigs = new ArrayList<ColumnConfig>();

        columnConfigs.add(selectionModel.getColumn());

        ColumnConfig column = new ColumnConfig("clientId", DVC_MSGS.deviceTableClientID(), 175);
        column.setSortable(true);
        selectionModel.getColumn();
        columnConfigs.add(column);

        column = new ColumnConfig("displayName", DVC_MSGS.deviceTableDisplayName(), 150);
        column.setSortable(true);
        columnConfigs.add(column);

        return columnConfigs;
}

And this is a screenshot of that part of app:

Could someone helps me how to all columns become selected when header checkbox is selected?