SubTableTemplate.java

import org.primefaces.component.column.Column;
import org.primefaces.component.columngroup.ColumnGroup;

    public List<Column> columns;

    public List<Column> getColumns() {        
        if(columns == null) {
            columns = new ArrayList<Column>();

            for(UIComponent child : this.getChildren()) {
                if(child.isRendered() && child instanceof Column) {
                    columns.add((Column) child);
                }
            }
        }

        return columns;
    }

    public ColumnGroup getColumnGroup(String target) {
        for(UIComponent child : this.getChildren()) {
            if(child instanceof ColumnGroup) {
                ColumnGroup colGroup = (ColumnGroup) child;
                String type = colGroup.getType();

                if(type != null && type.equals(target)) {
                    return colGroup;
                }

            }
        }

        return null;
    }