哈夫曼编码—文件的压缩与解压（Java）

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压缩代码

package cn.guizimo.huffmancode;

import java.io.*;
import java.util.*;

/**
 * @author guizimo
 * @date 2020/8/8 11:55 上午
 */
public class HuffmanCode {
    public static void main(String[] args) {
        String zipFile = "d://123.png";
        String dstFile = "d://123.zip";
        zipFile(zipFile, dstFile);;
        System.out.println("压缩成功!");
    }

    public static void unZipFile(String zipFile, String dstFile) {
        InputStream is = null;
        ObjectInputStream ois = null;
        OutputStream os = null;
        try {
            is = new FileInputStream(zipFile);
            ois = new ObjectInputStream(is);
            byte[] huffmanBytes = (byte[]) ois.readObject();
            Map<Byte, String> huffmanCodes = (Map<Byte, String>) ois.readObject();

            byte[] bytes = huffmanUnzip(huffmanCodes, huffmanBytes);
            os = new FileOutputStream(dstFile);
            os.write(bytes);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            try {
                os.close();
                ois.close();
                is.close();
            } catch (Exception e2) {
                System.out.println(e2.getMessage());
            }
        }
    }

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

    //哈夫曼解压
    private static byte[] huffmanUnzip(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));
        }

        //解码,反向编码表
        HashMap<String, Byte> map = new HashMap<>();
        for (Map.Entry<Byte, String> entry : huffmanCodes.entrySet()) {
            map.put(entry.getValue(), entry.getKey());
        }

        //根据编码扫描到对应的ASCLL码对应的字符
        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;
        }

        byte b[] = new byte[list.size()];
        for (int i = 0; i < b.length; i++) {
            b[i] = list.get(i);
        }
        return b;

    }

    //转化二进制
    private 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;
        }
    }


    //哈夫曼编码压缩
    private static byte[] huffmanZip(byte[] bytes) {
        List<Node> nodes = getNodes(bytes);
        //哈夫曼树
        Node huffmanTree = createHuffmanTree(nodes);
        //哈夫曼编码表
        Map<Byte, String> huffmanCodes = getCodes(huffmanTree);
        //哈夫曼编码
        byte[] zip = zip(bytes, huffmanCodes);
        return zip;
    }

    //压缩
    private static byte[] zip(byte[] bytes, Map<Byte, String> huffmanCodes) {
        StringBuilder stringBuilder = new StringBuilder();
        for (byte b : bytes) {
            stringBuilder.append(huffmanCodes.get(b));
        }
        int len;
        if (stringBuilder.length() % 8 == 0) {
            len = stringBuilder.length() / 8;
        } else {
            len = stringBuilder.length() / 8 + 1;
        }
        byte[] by = new byte[len];
        int index = 0;
        for (int i = 0; i < stringBuilder.length(); i += 8) {
            String strByte;
            if (i + 8 > stringBuilder.length()) {
                strByte = stringBuilder.substring(i);
                by[index] = (byte) Integer.parseInt(strByte, 2);
                index++;
            } else {
                strByte = stringBuilder.substring(i, i + 8);
                by[index] = (byte) Integer.parseInt(strByte, 2);
                index++;
            }
        }
        return by;
    }

    static Map<Byte, String> huffmanCodes = new HashMap<Byte, String>();
    static StringBuilder stringBuilder = new StringBuilder();

    //重载
    private static Map<Byte, String> getCodes(Node root) {
        if (root == null) {
            return null;
        }
        getCodes(root.left, "0", stringBuilder);
        getCodes(root.right, "1", stringBuilder);
        return huffmanCodes;
    }

    //获取哈夫曼编码
    private static void getCodes(Node node, String code, StringBuilder stringBuilder) {
        StringBuilder builder = new StringBuilder(stringBuilder);
        builder.append(code);
        if (node != null) {
            if (node.data == null) {  //递归
                getCodes(node.left, "0", builder);
                getCodes(node.right, "1", builder);
            } else {
                huffmanCodes.put(node.data, builder.toString());
            }
        }
    }

    //前序遍历
    private static void preOrder(Node root) {
        if (root != null) {
            root.preOrder();
        } else {
            System.out.println("哈夫曼树为空");
        }
    }

    //生成哈夫曼树
    private static Node createHuffmanTree(List<Node> nodes) {
        while (nodes.size() > 1) {
            Collections.sort(nodes);

            Node leftNode = nodes.get(0);
            Node rightNode = nodes.get(1);

            Node parent = new Node(null, leftNode.weight + rightNode.weight);
            parent.left = leftNode;
            parent.right = rightNode;

            nodes.remove(leftNode);
            nodes.remove(rightNode);
            nodes.add(parent);
        }
        return nodes.get(0);
    }

    //接收字节数组
    private static List<Node> getNodes(byte[] bytes) {
        List<Node> nodes = new ArrayList<>();
        Map<Byte, Integer> counts = new HashMap<>();
        for (byte b : bytes) {
            Integer count = counts.get(b);
            if (count == null) {
                counts.put(b, 1);
            } else {
                counts.put(b, count + 1);
            }
        }
        //遍历map
        for (Map.Entry<Byte, Integer> entry : counts.entrySet()) {
            nodes.add(new Node(entry.getKey(), entry.getValue()));
        }
        return nodes;
    }
}

class Node implements Comparable<Node> {
    Byte data;
    int weight; //字符出现的次数
    Node left;
    Node right;

    //前序遍历
    public void preOrder() {
        System.out.println(this);
        if (this.left != null) {
            this.left.preOrder();
        }
        if (this.right != null) {
            this.right.preOrder();
        }
    }

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

    @Override
    public int compareTo(Node o) {
        //从小到大排序
        return this.weight - o.weight;
    }

    @Override
    public String toString() {
        return "Node{" +
                "data=" + data +
                ", weight=" + weight +
                '}';
    }
}

解压代码

package cn.guizimo.huffmancode;

import java.io.*;
import java.util.*;

/**
 * @author guizimo
 * @date 2020/8/8 11:55 上午
 */
public class HuffmanCode {
    public static void main(String[] args) {
        String zipFile = "d://Uninstall.zip";
        String dstFile = "d://Uninstall2.xml";
        unZipFile(zipFile, dstFile);
        System.out.println("解压成功!");
    }

    public static void unZipFile(String zipFile, String dstFile) {
        InputStream is = null;
        ObjectInputStream ois = null;
        OutputStream os = null;
        try {
            is = new FileInputStream(zipFile);
            ois = new ObjectInputStream(is);
            byte[] huffmanBytes = (byte[]) ois.readObject();
            Map<Byte, String> huffmanCodes = (Map<Byte, String>) ois.readObject();

            byte[] bytes = huffmanUnzip(huffmanCodes, huffmanBytes);
            os = new FileOutputStream(dstFile);
            os.write(bytes);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            try {
                os.close();
                ois.close();
                is.close();
            } catch (Exception e2) {
                System.out.println(e2.getMessage());
            }
        }
    }

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

    //哈夫曼解压
    private static byte[] huffmanUnzip(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));
        }

        //解码,反向编码表
        HashMap<String, Byte> map = new HashMap<>();
        for (Map.Entry<Byte, String> entry : huffmanCodes.entrySet()) {
            map.put(entry.getValue(), entry.getKey());
        }

        //根据编码扫描到对应的ASCLL码对应的字符
        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;
        }

        byte b[] = new byte[list.size()];
        for (int i = 0; i < b.length; i++) {
            b[i] = list.get(i);
        }
        return b;

    }

    //转化二进制
    private 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;
        }
    }


    //哈夫曼编码压缩
    private static byte[] huffmanZip(byte[] bytes) {
        List<Node> nodes = getNodes(bytes);
        //哈夫曼树
        Node huffmanTree = createHuffmanTree(nodes);
        //哈夫曼编码表
        Map<Byte, String> huffmanCodes = getCodes(huffmanTree);
        //哈夫曼编码
        byte[] zip = zip(bytes, huffmanCodes);
        return zip;
    }

    //压缩
    private static byte[] zip(byte[] bytes, Map<Byte, String> huffmanCodes) {
        StringBuilder stringBuilder = new StringBuilder();
        for (byte b : bytes) {
            stringBuilder.append(huffmanCodes.get(b));
        }
        int len;
        if (stringBuilder.length() % 8 == 0) {
            len = stringBuilder.length() / 8;
        } else {
            len = stringBuilder.length() / 8 + 1;
        }
        byte[] by = new byte[len];
        int index = 0;
        for (int i = 0; i < stringBuilder.length(); i += 8) {
            String strByte;
            if (i + 8 > stringBuilder.length()) {
                strByte = stringBuilder.substring(i);
                by[index] = (byte) Integer.parseInt(strByte, 2);
                index++;
            } else {
                strByte = stringBuilder.substring(i, i + 8);
                by[index] = (byte) Integer.parseInt(strByte, 2);
                index++;
            }
        }
        return by;
    }

    static Map<Byte, String> huffmanCodes = new HashMap<Byte, String>();
    static StringBuilder stringBuilder = new StringBuilder();

    //重载
    private static Map<Byte, String> getCodes(Node root) {
        if (root == null) {
            return null;
        }
        getCodes(root.left, "0", stringBuilder);
        getCodes(root.right, "1", stringBuilder);
        return huffmanCodes;
    }

    //获取哈夫曼编码
    private static void getCodes(Node node, String code, StringBuilder stringBuilder) {
        StringBuilder builder = new StringBuilder(stringBuilder);
        builder.append(code);
        if (node != null) {
            if (node.data == null) {  //递归
                getCodes(node.left, "0", builder);
                getCodes(node.right, "1", builder);
            } else {
                huffmanCodes.put(node.data, builder.toString());
            }
        }
    }

    //前序遍历
    private static void preOrder(Node root) {
        if (root != null) {
            root.preOrder();
        } else {
            System.out.println("哈夫曼树为空");
        }
    }

    //生成哈夫曼树
    private static Node createHuffmanTree(List<Node> nodes) {
        while (nodes.size() > 1) {
            Collections.sort(nodes);

            Node leftNode = nodes.get(0);
            Node rightNode = nodes.get(1);

            Node parent = new Node(null, leftNode.weight + rightNode.weight);
            parent.left = leftNode;
            parent.right = rightNode;

            nodes.remove(leftNode);
            nodes.remove(rightNode);
            nodes.add(parent);
        }
        return nodes.get(0);
    }

    //接收字节数组
    private static List<Node> getNodes(byte[] bytes) {
        List<Node> nodes = new ArrayList<>();
        Map<Byte, Integer> counts = new HashMap<>();
        for (byte b : bytes) {
            Integer count = counts.get(b);
            if (count == null) {
                counts.put(b, 1);
            } else {
                counts.put(b, count + 1);
            }
        }
        //遍历map
        for (Map.Entry<Byte, Integer> entry : counts.entrySet()) {
            nodes.add(new Node(entry.getKey(), entry.getValue()));
        }
        return nodes;
    }
}

class Node implements Comparable<Node> {
    Byte data;
    int weight; //字符出现的次数
    Node left;
    Node right;

    //前序遍历
    public void preOrder() {
        System.out.println(this);
        if (this.left != null) {
            this.left.preOrder();
        }
        if (this.right != null) {
            this.right.preOrder();
        }
    }

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

    @Override
    public int compareTo(Node o) {
        //从小到大排序
        return this.weight - o.weight;
    }

    @Override
    public String toString() {
        return "Node{" +
                "data=" + data +
                ", weight=" + weight +
                '}';
    }
}

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原文链接：https://www.cnblogs.com/guizimo/p/13457996.html

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