压缩算法核心代码Java

应工作需要，研究了下压缩算法思想，分享如下：

1. Compress radio = compressedSize/origSize

2. 重复现象是具有局部性的，这是压缩算法思想的基础

3. 基础操作：
   8bit转byte：
   Integer i = Integer.parseInt(8bitStr, 2);
   // byte 与 int 的相互转换
   public static byte intToByte(int x) {
   return (byte) x;
   }
   byte中取bit：
   public static String getBit(byte by, int n) {
   StringBuffer sb = new StringBuffer();
   for (int i = n - 1; i >= 0; i–) {
   sb.append((by >> i) & 0x1);
   }
   return sb.toString();
   }

4. io流

   dis = new DataInputStream(new FileInputStream(f)); // 实例化数据输入流对象
   while (-1 != (len = dis.read(orig, 0, fileSize))) {
   encode（orig）；
   ｝
   OR
   byte[] buffer = new byte[(int) fileSize];

    int offset = 0;
   
    int numRead = 0;
   
    while (offset < buffer.length
   
    		&& (numRead = fi.read(buffer, offset, buffer.length - offset)) >= 0) {
   
    	offset += numRead;
   
    }
   
    // 确保所有数据均被读取
   
    if (offset != buffer.length) {
    	fi.close();
    	throw new IOException("Could not completely read file " + file.getName());
    }
   

5. LZ77算法代码：

	public void encode(byte[] orig) {
		int step = 0;
		int origLength = orig.length;
		while (!isLookHeadEmpty(origLength)) {
			winMove();
			int[] info = findMaxMatch(orig);
			setMoveSteps(info[1]);
			if (info[1] == 0) {
				byte next = orig[windSpiltIndex];
				nextEncode = "1" + getBit(next);
			} else {
				nextEncode = "01" + getBit(intToByte(info[0]), 6) + getBit(intToByte(info[1]), 3);
			}
			step++;
			commit();
		}
		writeFile();
	}
	private boolean isLookHeadEmpty(int length) {
		if (windSpiltIndex + move > length - 1) {
			return true;
		}
		return false;
	}
	private void winMove() {
		windSpiltIndex += move;
	}
	public int[] findMaxMatch(byte[] orig) {
		int[] maxInfo = { 0, 0 };
		int maxLen = 0;
		int markStart = 0;
		int tmp = -1;
		System.out.println(windSpiltIndex);
		for (int i = windSpiltIndex + minMatchNum; i <= minEdge(orig.length); i++) {
			System.out.print("str1: ");
			print(orig, getWinStartIndex(), windSpiltIndex - 1);
			System.out.print("str2: ");
			print(orig, windSpiltIndex, i - 1);
			tmp = lastIndexOf(orig, getWinStartIndex(), windSpiltIndex - getWinStartIndex(), orig, windSpiltIndex,
					i - windSpiltIndex, windSpiltIndex);
			System.out.println("tmp = " + tmp);
			if (tmp > -1) {
				markStart = windSpiltIndex - getWinStartIndex() - tmp - 1;
				maxLen = i - windSpiltIndex;
			} else {
				break;
			}
		}
		maxInfo[0] = markStart;
		maxInfo[1] = maxLen;
		move = maxLen;
		return maxInfo;
	}
		private int getWinStartIndex() {
		if (windSpiltIndex - searchSize < 1) {
			return 0;
		}
		return windSpiltIndex - searchSize;
	}

	private int minEdge(int length) {
		if (windSpiltIndex + lookAheadBufferSize >= length) {
			return length;
		}
		return windSpiltIndex + lookAheadBufferSize;
	}
	public static String getBit(byte by, int n) {
		StringBuffer sb = new StringBuffer();
		for (int i = n - 1; i >= 0; i--) {
			sb.append((by >> i) & 0x1);
		}
		return sb.toString();
	}
	private void commit() {
		String tmp = restBuf + nextEncode;
		System.out.println("tmp length : " + tmp.length());
		int i = 0;
		for (i = 0; i < tmp.length() / 8; i++) {
			putToArray(tmp.substring(i * 8, i * 8 + 8));
		}
		restBuf = tmp.substring(i * 8, tmp.length());
	}

	private void putToArray(String tmp) {
		System.out.print("byte : " + tmp);
		Integer i = Integer.parseInt(tmp, 2);
		System.out.print(" " + i);
		// Integer i = Integer.valueOf(tmp, 2); // tmp为二进制字符串
		// byte[] b = i.toString().getBytes();
		System.out.print(" " + intToByte(i) + " \n");
		byteArr[cur++] = intToByte(i);
	}
	private void setMoveSteps(int i) {
		if (i == 0) {
			move = 1;
		} else {
			move = i;
		}
	}
	private void writeFile() {
		System.out.println();
		System.out.println("pair sum :" + pair);
		System.out.println("small :" + small);
		System.out.println("pairlength :" + pairLength);
		System.out.println("rest length: " + restBuf.length());
		for (int i = 0; i < pairArr.length; i++) {
			System.out.println(i + ":" + pairArr[i]);
		}
		int tmp = 8 - restBuf.length();
		for (int i = 0; i < tmp; i++) {
			restBuf += "0";
		}
		putToArray(restBuf);

		String fileName = lz77encodeOutPath;
		try {
			// 将DataOutputStream与FileOutputStream连接可输出不同类型的数据
			// FileOutputStream类的构造函数负责打开文件kuka.dat，如果文件不存在，
			// 则创建一个新的文件，如果文件已存在则用新创建的文件代替。然后FileOutputStream
			// 类的对象与一个DataOutputStream对象连接，DataOutputStream类具有写
			// 各种数据类型的方法。
			DataOutputStream out = new DataOutputStream(new FileOutputStream(fileName));
			out.write(byteArr, 0, cur);
			avgList.add(cur);
			out.close();
		} catch (Exception e) {
			e.printStackTrace();
		}

	}

6. 解码算法

public void decode() {
		Out();
		int offset = 0;
		int length = 0;
		while (true) {
			if (getBits(1).equals("1")) {
				String tmp = getBits(8);
				System.out.println("out: " + tmp);
				decoded[outCur++] = bit2byte(tmp);
				addElement(tmp);

			} else if (getBits(1).equals("1")) {
				offset = Integer.valueOf(bit2byte(getBits(6)));
				length = Integer.valueOf(bit2byte(getBits(3)));
				if (length == 0) {
					length = 8;
				}
				System.out.println(offset);
				offset = getEdge() / 8 - offset - 1;
				System.out.println("offset: " + offset);
				System.out.println("length: " + length);
				String tmp = winStr.substring(offset * 8, offset * 8 + length * 8);
				System.out.println("out: " + tmp);
				for (int i = 0; i < length; i++) {
					String ttmp = winStr.substring((offset + i) * 8, (offset + i + 1) * 8);
					decoded[outCur++] = bit2byte(ttmp);
				}
				addElement(tmp);
			} else {
				System.out.println("end of file");
				break;
			}
		}
		writeFile();

	}