Flex文件上传功能。实现基于Flex/Flash的文件上传功能，从本地选择文件，上传至指定的URL。该程序不足之处在于：一是无法同时上传多个文件，二是无法支持会话（会话支持受Flex本身的限制）。-Flex file upload function. Flex/Flash-based file upload function, select a file from the local, upload to the specified URL. The inadequacies of the program is: One can not upload multiple files at the same time, and can not support session (session support by Flex restrictions).