使用“Openxml writer”在Excel中合并单元格

I want to merge cells is excel. By using DOM approach I can do it easily. But as my excel file is too large, when I tries to get worksheet it throws Out of memory exception. So I have to use SAX approach to read excel file. But I dont know how to merge cells in this approach. Searched a lot but every one gives the solution of DOM approach.I want to merge cells is excel. By using DOM ap