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());    }

1. 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();        }    }

1. 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();    }