Using a Java-COM Bridge like J-Integra for COM, you can easily access/modify MS Excel from Java client. You can find more information about it at http://j-integra.intrinsyc.com
J-Integra for COM's pure Java runtime talks to COM components using Distributed COM (DCOM) layered over Remote Procedure Calls (RPC). The RPCs are themselves layered on TCP/IP. Therefore, at the lowest level, J-Integra for COM uses standard Java networking classes.
Here's an very simple example to show you how easy to access Excel from Java client:
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