java写的文件多线程下载程序，很简单，没有界面，突出重点，n年前写的，结合了两个网上的程序写的，希望起到抛砖引玉的作用。-java file multi-threaded download process is very simple, there is no interface, focused, n years to write, combines two online writing program, and I hope to play a valuable role.