赫夫曼编码实现文件的压缩和解压缩

传说中没有注释的代码
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import java.io.*;
import java.util.*;

public class HuffmanCodeDemo {

    public static void main(String[] args) {

        String srcFile = "C:\\Users\\Administrator\\Desktop\\lj.zip";
        String dstFile = "C:\\Users\\Administrator\\Desktop\\ywl.bmp";
//        zipFile(srcFile, dstFile);
        decompressFile(srcFile, dstFile);
    }

    public static void zipFile(String srcFile, String dstFile) {
        InputStream is = null;
        OutputStream os = null;
        ObjectOutputStream oos = null;
        try {
            is = new FileInputStream(srcFile);
            byte[] b = new byte[is.available()];
            is.read(b);
            byte[] bytes = huffmanZip(b);
            os = new FileOutputStream(dstFile);
            oos = new ObjectOutputStream(os);
            oos.writeObject(bytes);
            oos.writeObject(huffmanCode);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            try {
                oos.close();
                os.close();
                is.close();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }
    }

    public static void decompressFile(String srcFile, String dstFile) {
        InputStream is = null;
        ObjectInputStream ois = null;
        OutputStream os = null;
        try {
            is = new FileInputStream(srcFile);
            ois = new ObjectInputStream(is);
            byte[] bytes = (byte[]) ois.readObject();
            HashMap<Byte, String> map = (HashMap<Byte, String>) ois.readObject();
            byte[] decode = decode(map, bytes);
            os = new FileOutputStream(dstFile);
            os.write(decode);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            try {
                os.close();
                ois.close();
                is.close();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }
    }

    public static byte[] huffmanZip(byte[] bytes) {
        ArrayList<Node> nodes = getNodes(bytes);
        Node huffmanTreeRoot = createHuffmanTree(nodes);
        getCodes(huffmanTreeRoot);
        byte[] zip = zip(bytes, huffmanCode);
        return zip;

    }

    public static byte[] decode(Map<Byte, String> huffmanCodes, byte[] huffmanBytes) {
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < huffmanBytes.length; i++) {
            byte b = huffmanBytes[i];
            boolean flag = !(i == (huffmanBytes.length - 1));
            stringBuilder.append(byteToBitString(flag, b));
        }
        Map<String, Byte> map = new HashMap<>();
        for (Map.Entry<Byte, String> entry : huffmanCodes.entrySet()) {
            map.put(entry.getValue(), entry.getKey());
        }
        List<Byte> list = new ArrayList<>();
        for (int i = 0; i < stringBuilder.length(); ) {
            int count = 1;
            boolean flag = true;
            Byte b = null;

            while (flag) {
                String key = stringBuilder.substring(i, i + count);
                b = map.get(key);
                if (b == null) {
                    count++;
                } else {
                    flag = false;
                }
            }
            list.add(b);
            i += count;
        }
        int size = list.size();
        byte[] b = new byte[size];
        for (int i = 0; i < size; i++) {
            b[i] = list.get(i);
        }
        return b;

    }

    public static String byteToBitString(boolean flag, byte b) {
        int temp = b;
        if (flag) {
            temp |= 256;
        }
        String str = Integer.toBinaryString(temp);
        if (flag) {
            return str.substring(str.length() - 8);
        } else {
            return str;
        }

    }


    public static ArrayList<Node> getNodes(byte[] bytes) {
        ArrayList<Node> list = new ArrayList<>();
        HashMap<Byte, Integer> counts = new HashMap<>();
        int len = bytes.length;
        for (int i = 0; i < len; i++) {
            Integer count = counts.get(bytes[i]);
            if (count == null) {
                counts.put(bytes[i], 1);
            } else {
                counts.put(bytes[i], count + 1);
            }
        }
        for (Map.Entry<Byte, Integer> entry : counts.entrySet()) {
            list.add(new Node(entry.getKey(), entry.getValue()));
        }
        return list;
    }

    public static Node createHuffmanTree(ArrayList<Node> nodes) {
        while (nodes.size() > 1) {
            Collections.sort(nodes);
            Node leftNode = nodes.get(0);
            Node rightNode = nodes.get(1);
            nodes.remove(leftNode);
            nodes.remove(rightNode);
            Node parent = new Node(null, leftNode.weight + rightNode.weight);
            parent.left = leftNode;
            parent.right = rightNode;
            nodes.add(parent);
        }
        return nodes.get(0);
    }

    static HashMap<Byte, String> huffmanCode = new HashMap<>();

    public static void getCodes(Node huffmanTreeRoot) {
        StringBuilder stringBuilder = new StringBuilder();
        if (huffmanTreeRoot != null) {
            getCodes(huffmanTreeRoot.left, "0", stringBuilder);
            getCodes(huffmanTreeRoot.right, "1", stringBuilder);
        } else {
            System.out.println("赫夫曼树根节点为空~");
        }
    }

    public static void getCodes(Node node, String code, StringBuilder builder) {
        StringBuilder stringBuilder = new StringBuilder(builder);
        if (node != null) {
            stringBuilder.append(code);
            if (node.data != null) {
                huffmanCode.put(node.data, stringBuilder.toString());
            }
            getCodes(node.left, "0", stringBuilder);
            getCodes(node.right, "1", stringBuilder);
        }

    }

    public static byte[] zip(byte[] bytes, Map<Byte, String> huffmanCodes) {
        StringBuilder builder = new StringBuilder();
        for (byte b : bytes) {
            builder.append(huffmanCodes.get(b));
        }
        int len = (builder.length() + 7) / 8;
        byte[] zipByte = new byte[len];
        int index = 0;
        String str;
        for (int i = 0; i < builder.length(); i += 8) {
            if (i + 8 <= builder.length()) {
                str = builder.substring(i, i + 8);
            } else {
                str = builder.substring(i);
            }
            byte b = (byte) Integer.parseInt(str, 2);
            zipByte[index++] = b;
        }
        return zipByte;
    }

}

class Node implements Comparable<Node> {
    public Byte data;
    public int weight;
    public Node left;
    public Node right;

    public Node(Byte data, int weight) {
        this.data = data;
        this.weight = weight;
    }

    @Override
    public int compareTo(Node o) {
        return this.weight - o.weight;
    }

}

原图片：

压缩后：

解压后：