JAVA I/O判断读入的文件的文件编码

package encoding;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;

public class Encoding {
	public static void main(String[] args) {
		String charset = getCharset(new File("C://login.txt"));
		System.out.println(charset);
	}

	public static String getCharset(File file) {
		String charset = "GBK";
		byte[] first3Bytes = new byte[3];
		try {
			boolean checked = false;
			BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
			bis.mark(0);
			int read = bis.read(first3Bytes, 0, 3);
			if (read == -1)
				return charset;
			if (first3Bytes[0] == (byte) 0xFF && first3Bytes[1] == (byte) 0xFE) {
				charset = "UTF-16LE";
				checked = true;
			} else if (first3Bytes[0] == (byte) 0xFE&& first3Bytes[1] == (byte) 0xFF) {
				charset = "UTF-16BE";
				checked = true;
			} else if (first3Bytes[0] == (byte) 0xEF && first3Bytes[1] == (byte) 0xBB && first3Bytes[2] == (byte) 0xBF) {
				charset = "UTF-8";
				checked = true;
			}
			bis.reset();
			if (!checked) {
				int loc = 0;
				while ((read = bis.read()) != -1) {
					loc++;
					if (read >= 0xF0)
						break;
					if (0x80 <= read && read <= 0xBF)
						break;
					if (0xC0 <= read && read <= 0xDF) {
						read = bis.read();
						if (0x80 <= read && read <= 0xBF)
							continue;
						else
							break;
					} else if (0xE0 <= read && read <= 0xEF) {
						read = bis.read();
						if (0x80 <= read && read <= 0xBF) {
							read = bis.read();
							if (0x80 <= read && read <= 0xBF) {
								charset = "UTF-8";
								break;
							} else
								break;
						} else
							break;
					}
				}
				System.out.println(loc + " " + Integer.toHexString(read));
			}

			bis.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return charset;
	}
}