IO 流读取文件时候出现乱码 文件编码格式问题 怎么转换解决方法

在使用下面这个写法时候UTF-8文件编码 在读取时候出现乱码问题。
File myFile=new File("文件路径");

 BufferedReader in = new BufferedReader(new FileReader(myFile));

应该修改为：

 BufferedReader in = new BufferedReader(new InputStreamReader(
					new FileInputStream(myFile), "UTF-8"));

如果使用INSA编码时候 请使用下面文件读取方式：

InputStreamReader reader = new InputStreamReader(
						new FileInputStream(new File("文件路径")), "gb2312");

下面是我对文件编码的判断方法：

/**
	 * 上传文件编码判断
	 * */
	public static String get_charset(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 len = 0;
				int loc = 0;

				while ((read = bis.read()) != -1) {
					loc++;
					if (read >= 0xF0)
						break;
					if (0x80 <= read && read <= 0xBF) // 单独出现BF以下的，也算是GBK
						break;
					if (0xC0 <= read && read <= 0xDF) {
						read = bis.read();
						if (0x80 <= read && read <= 0xBF) // 双字节 (0xC0 - 0xDF)
							// (0x80
							// - 0xBF),也可能在GB编码内
							continue;
						else
							break;
					} else if (0xE0 <= read && read <= 0xEF) {// 也有可能出错，但是几率较小
						read = bis.read();
						if (0x80 <= read && read <= 0xBF) {
							read = bis.read();
							if (0x80 <= read && read <= 0xBF) {
								charset = "UTF-8";
								break;
							} else
								break;
						} else
							break;
					}
				}

			}

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

		return charset;
	}

调用时候判断编码方式UTF-8 或是 INSA编码：

BufferedReader br = null;
			if (charset == "GBK") {
				InputStreamReader reader = new InputStreamReader(
						new FileInputStream(new File(filepath)), "gb2312");
				br = new BufferedReader(reader);
			}
			if (charset == "UTF-8") {
				br = new BufferedReader(new InputStreamReader(
						new FileInputStream(filepath), "UTF-8"));
			}