如何将多个Excel文件合并为具有多个工作表的单个Excel工作簿？

I need to develop a service (either WCF or Java) that can take multiple single-sheet Excel files and combine them into a single Excel workbook with multiple sheets. The Excel files are actually exported from crystal reports as individual files. Following are some of the requirements of the service:I need to develop a service (either WCF or Java