File subDir=new File("c:\\mp3");
if(subDir.isDirectory()){// 是目录
}File mp3=new File("c:\\mp3\\avemaria.mp3");if(mp3.isFile()){// 是文件
}

File dir = new File(fromDir);
String[] children = dir.list();for (int i=0; i<children.length; i++) {String filename = children[i];...
}

public static void copyFile(File sourceFile, File targetFile) throws IOException {BufferedInputStream inBuff = null;BufferedOutputStream outBuff = null;try {// 新建文件输入流并对它进行缓冲inBuff = new BufferedInputStream(new FileInputStream(sourceFile));// 新建文件输出流并对它进行缓冲outBuff = new BufferedOutputStream(new FileOutputStream(targetFile));// 缓冲数组byte[] b = new byte[1024 * 5];int len;while ((len = inBuff.read(b)) != -1) {outBuff.write(b, 0, len);}// 刷新此缓冲的输出流
            outBuff.flush();} finally {// 关闭流if (inBuff != null)inBuff.close();if (outBuff != null)outBuff.close();}}

/*** 将文件上传到服务器，返回在服务器的路径文件名* @param in* @param filename* @return* @throws Exception*/public String upload2Server(InputStream in, String filename) throws Exception {BufferedInputStream inBuff = null;BufferedOutputStream outBuff = null;try {// 新建文件输入流并对它进行缓冲inBuff = new BufferedInputStream(in);// 新建文件输出流并对它进行缓冲String filePathname=uploadPath+getTimePrefix()+filename;outBuff = new BufferedOutputStream(new FileOutputStream(new File(filePathname)));// 缓冲数组byte[] b = new byte[1024 * 5];int len;while ((len = inBuff.read(b)) != -1) {outBuff.write(b, 0, len);}// 刷新此缓冲的输出流
            outBuff.flush();return filePathname;} catch(Exception ex){logger.error(ex);throw ex;}finally {// 关闭流if (inBuff != null)inBuff.close();if (outBuff != null)outBuff.close();}}

String folder=System.getProperty("java.io.tmpdir");