模拟PPP协议0比特填充

import java.io.UnsupportedEncodingException;

/**
 * 编码类 
 * 功能：模拟PPP协议字节填充的编码过程
*/

public class Code {

	// 把字符串的长度填充到8
	private String fillEight(String str) {
		if (str.length() < 8) {
			str = "0" + str;
			str = fillEight(str);
		}
		return str;
	}

	// 返回数据部分二进制形式的字符串
	private String getDataByte(byte[] b) {
		String str = "";
		for (int temp : b) {
			temp &= 0xff; // 将高24位变成全0
			str += fillEight(Integer.toBinaryString(temp));
		}
		return str;
	}

	// 对字符串进行字节填充
	private String fillByte(String str) {
		int count = 0; // 计算连续的1的个数
		for (int i = 0; i < str.length(); i++) {
			if (str.charAt(i) == '1') {
				count++;
			} else {
				count = 0;
			}
			if (count == 5) {
				str = str.substring(0,i + 1) + "0"
						+ fillByte(str.substring(i + 1));
				return str;
			}
		}
		return str;
	}

	// 对数据进行封装
	private String packaging(String str) {
		if (str.length() > 1500) {
			str = packaging(str.substring(0,1500))
					+ packaging(str.substring(1500));
			return str;
		} else {
			return "01111110" + str + "01111110";
		}
	}

	// 返回编码后的字符串
	public static String getCodedString(String str)
			throws UnsupportedEncodingException {
		return getCodedString(str.getBytes("UTF-8"));
	}

	// 返回编码后的字符串
	public static String getCodedString(byte[] b)
			throws UnsupportedEncodingException {
		Code code = new Code();
		return code.packaging(code.fillByte(code.getDataByte(b)));
	}

}

import java.io.UnsupportedEncodingException;

/**
 * 解码类 
* 功能：模拟PPP协议字节填充的解码过程
*/

public class Decode {

	// 返回数据部分二进制形式的字符串
	private String getData(String str) {
		System.out.println(str.length());
		String strBuffer = "";
		int start = str.indexOf("01111110") + 8;
		int end = str.indexOf("01111110",start);
		System.out.println(start + " " + end);
		if (start >= end) {
			return "";
		}
		strBuffer = str.substring(start,end);
		if (end + 8 < str.length()) {
			strBuffer += getData(str.substring(end + 8));
		}
		System.out.println(strBuffer.length());
		return strBuffer;
	}

	// 抽出字符串的填充字节
	private String removeByte(String str) {
		int count = 0; // 计算连续的1的个数
		for (int i = 0; i < str.length(); i++) {
			if (str.charAt(i) == '1') {
				count++;
			} else {
				count = 0;
			}
			if (count == 5) {
				str = str.substring(0,i + 1)
						+ removeByte(str.substring(i + 2));
				return str;
			}
		}
		return str;
	}

	// 返回数据的byte型数组
	private byte[] getBytes(String str) {
		int length = str.length() / 8,temp;
		byte b[] = new byte[length];
		for (int i = 0; i < length; i++) {
			temp = Integer.parseInt(str.substring(8 * i,8 * (i + 1)),2);
			b[i] = (byte) temp;
		}
		return b;
	}

	// 返回解码后的字符串
	public static String getString(String str)
			throws UnsupportedEncodingException {
		Decode decode = new Decode();
		return getString(decode
				.getBytes(decode.removeByte(decode.getData(str))));
	}

	// 返回解码后的字符串
	public static String getString(byte[] b)
			throws UnsupportedEncodingException {
		return new String(b,"UTF-8");
	}

}