赫夫曼编码

public class HuffmanCode {
    public static void main(String[] args) {
        String content = "i like like like java do you like a java";
        byte[] contentBytes = content.getBytes();
        System.out.println(contentBytes.length);//40

//        List<Node> nodes = getNodes(contentBytes);
//        System.out.println(nodes);
//
//        Node huffmanTreeRoot = createHuffmanTree(nodes);
//        preOrder(huffmanTreeRoot);
//
//        Map<Byte, String> huffmanCodes = getCodes(huffmanTreeRoot);
//        System.out.println("生成的哈夫曼编码表:" + huffmanCodes);
//
//        byte[] huffmanCodeBytes = zip(contentBytes, huffmanCodes);
//        System.out.println("huffmanCodeBytes=" + huffmanCodeBytes);

        byte[] huffmanCodeBytes = huffmanZip(contentBytes);
        System.out.println("压缩后数组=" + Arrays.toString(huffmanCodeBytes));
        System.out.println("长度=" + huffmanCodeBytes.length);

        byte b = -1;
        System.out.println(byteToBit(true, b));

        byte[] decodeBytes = decode(huffmanCodes, huffmanCodeBytes);
        System.out.println("decodeBytes=" + new String(decodeBytes));

        //测试压缩文件
        String srcFile = "f:\\src.png";
        String dstFile = "f:\\dst.png";
        zipFile(srcFile, dstFile);
        System.out.println("压缩文件成功");

        //测试解压文件
        String zipFile = "f:\\dst.png";
        String dstFile2 = "f:\\src2.png";
        unzipFile(zipFile,dstFile2);
        System.out.println("解压文件成功");


    }

    /**
     * 解压文件
     *
     * @param zipFile 准备解压的文件
     * @param dstFile 文件解压路径
     */
    public static void unzipFile(String zipFile, String dstFile) {
        //定义文件的输入流
        InputStream is = null;
        //定义对象输入流
        ObjectInputStream ois = null;
        //定义文件的输出流
        OutputStream os = null;

        try {
            is = new FileInputStream(zipFile);
            ois = new ObjectInputStream(is);
            byte[] huffmanBytes = (byte[]) ois.readObject();
            //读取赫夫曼编码表
            Map<Byte, String> huffmanCodes = (Map<Byte, String>) ois.readObject();

            //解码
            byte[] bytes = decode(huffmanCodes, huffmanBytes);
            //将bytes数组写入目标文件
            os = new FileOutputStream(dstFile);
            //写数据到文件中
            os.write(bytes);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            try {
                os.close();
                ois.close();
                is.close();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }
    }

    /**
     * 文件压缩
     *
     * @param srcFile 原文件路径
     * @param dstFile 压缩文件目录
     */
    public static void zipFile(String srcFile, String dstFile) {
        //创建输出流
        OutputStream os = null;
        ObjectOutputStream oos = null;
        //创建文件输入流
        FileInputStream is = null;
        try {
            is = new FileInputStream(srcFile);
            //创建和原文件一样大小的byte数组
            byte[] b = new byte[is.available()];
            //读取文件
            is.read(b);
            //获取文件对应的赫夫曼编码表
            byte[] huffmanBytes = huffmanZip(b);
            //创建输出流，存放压缩文件
            os = new FileOutputStream(dstFile);
            //创建一个和文件输出流相关的ObjectOutputStream
            oos = new ObjectOutputStream(os);
            //把赫夫曼编码后的文件写入压缩文件
            oos.writeObject(huffmanBytes);
            //以对象流的方式写入赫夫曼编码，是为了恢复源文件时使用
            //注意一定要把赫夫曼编码写入压缩文件
            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());
            }
        }

    }

    /**
     * @param huffmanCodes 赫夫曼编码表
     * @param huffmanBytes 赫夫曼编码得到的字节数组
     * @return 原来字符串对应的数组
     */
    private static byte[] decode(Map<Byte, String> huffmanCodes, byte[] huffmanBytes) {
        StringBuilder stringBuilder = new StringBuilder();

        for (int i = 0; i < huffmanBytes.length; i++) {
            boolean flag = (i == huffmanBytes.length - 1 ? false : true);
            stringBuilder.append(byteToBit(flag, huffmanBytes[i]));
        }
        //把字符串按照指定的赫夫曼编码进行解码
        //把赫夫曼编码表反向转换，因为需要反向查找
        Map<String, Byte> map = new HashMap<>();
        for (Map.Entry<Byte, String> entry : huffmanCodes.entrySet()) {
            map.put(entry.getValue(), entry.getKey());
        }
        //创建集合存放byte
        List<Byte> list = new ArrayList<>();
        for (int i = 0; i < stringBuilder.length(); ) {
            int count = 1;
            boolean flag = true;
            while (flag) {
                String key = stringBuilder.substring(i, i + count);
                Byte b = map.get(key);
                if (b != null) {
                    flag = false;
                    i = i + count;
                    list.add(b);
                } else {
                    count++;
                }
            }
        }
        System.out.println(list);
        byte[] decodeBytes = new byte[list.size()];
        for (int i = 0; i < list.size(); i++) {
            decodeBytes[i] = list.get(i);
        }
        return decodeBytes;
    }

    /**
     * @param flag 标识是否需要补高位,如果是最后一个字节，无需补高位
     * @param b
     * @return b对应的二进制的字符串(注意是按补码返回)
     */
    private static String byteToBit(boolean flag, byte b) {
        int temp = b;
        //正数需要补高位
        if (flag) {
            temp |= 256;
        }
        String str = Integer.toBinaryString(temp);//返回的是temp对应的二进制的补码
        if (flag) {
            return str.substring(str.length() - 8);
        } else {
            return str;
        }
    }

    /**
     * 封装
     *
     * @param bytes 原始字符串对应的字节数组
     * @return 经过赫夫曼编码后的字节数组
     */
    private static byte[] huffmanZip(byte[] bytes) {

        List<Node> nodes = getNodes(bytes);
        //根据nodes创建赫夫曼树
        Node huffmanTreeRoot = createHuffmanTree(nodes);
        //生成对应的赫夫曼编码
        Map<Byte, String> huffmanCodes = getCodes(huffmanTreeRoot);
        //根据赫夫曼编码压缩得到压缩后的赫夫曼编码字节数组
        byte[] huffmanCodeBytes = zip(bytes, huffmanCodes);
        return huffmanCodeBytes;
    }

    /**
     * 将字符串通过生成的赫夫曼编码表返回赫夫曼编码压缩后的byte数组
     *
     * @param bytes        原始的字符串数组对应的byte数组
     * @param huffmanCodes 生成的赫夫曼编码表
     * @return byte[]huffmanCodeBytes, 即8位对应一个byte，放入到huffmanCodeBytes
     * huffmanCodeBytes[0] = 10101000 =>byte[推导 10101000=>10100111(反码)=>11011000]
     */
    private static byte[] zip(byte[] bytes, Map<Byte, String> huffmanCodes) {
        StringBuilder stringBuilder = new StringBuilder();
        for (byte b : bytes) {
            stringBuilder.append(huffmanCodes.get(b));
        }
        //统计返回的长度
        //int len = (stringBuilder.length() + 7) / 8;
        int len;
        if (stringBuilder.length() % 8 == 0) {
            len = stringBuilder.length() / 8;
        } else {
            len = stringBuilder.length() / 8 + 1;
        }

        //创建存储压缩后的byte数组
        byte[] huffmanCodeBytes = new byte[len];
        int index = 0;//记录第几个byte

        for (int i = 0; i < stringBuilder.length(); i = i + 8) {
            String strByte;
            if (i + 8 > stringBuilder.length()) {
                strByte = stringBuilder.substring(i);
            } else {
                strByte = stringBuilder.substring(i, i + 8);

            }

            //将strByte转成一个byte，放入到huffmanCodeBytes
            huffmanCodeBytes[index] = (byte) Integer.parseInt(strByte, 2);
            index++;
        }
        return huffmanCodeBytes;
    }


    //生成赫夫曼编码表
    //1、将赫夫曼编码表放在map中
    static Map<Byte, String> huffmanCodes = new HashMap<>();
    //2、拼接路径，定义一个StringBuilder存储某个叶子节点的路径
    static StringBuilder stringBuilder = new StringBuilder();

    //为了调用方便，重载getCodes方法
    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;
    }

    /**
     * @param node          传入节点
     * @param code          路径：左子节点0，右子节点1
     * @param stringBuilder 用于拼接路径
     */
    private static void getCodes(Node node, String code, StringBuilder stringBuilder) {
        StringBuilder stringBuilder2 = new StringBuilder(stringBuilder);
        //将code加入到stringBuilder2
        stringBuilder2.append(code);
        if (node != null) {
            if (node.data == null) {//非叶子节点
                //递归处理
                //向左
                getCodes(node.left, "0", stringBuilder2);
                //向右
                getCodes(node.right, "1", stringBuilder2);

            } else {
                //找到了某个叶子节点的最后
                huffmanCodes.put(node.data, stringBuilder2.toString());
            }
        }

    }

    private static List<Node> getNodes(byte[] bytes) {
        ArrayList<Node> nodes = new ArrayList<>();
        //遍历bytes，统计每个字符出现的次数，用map记录
        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);
            }

        }
        //将map转成Node对象，并加入nodes集合中
        for (Map.Entry<Byte, Integer> entry : counts.entrySet()) {
            nodes.add(new Node(entry.getKey(), entry.getValue()));
        }
        return nodes;
    }


    public static Node createHuffmanTree(List<Node> nodes) {
        while (nodes.size() > 1) {
            //排序
            Collections.sort(nodes);

            //取出第一颗权值最小的二叉树
            Node leftNode = nodes.get(0);
            //第二小的
            Node righNode = nodes.get(1);
            //创建一个新的二叉树,它的根节点没有data，只有权值
            Node parent = new Node(null, leftNode.weight + righNode.weight);
            parent.left = leftNode;
            parent.right = righNode;

            //将处理过的两颗二叉树从nodes中移除
            nodes.remove(leftNode);
            nodes.remove(righNode);
            //将新的二叉树加入到nodes
            nodes.add(parent);
        }
        //最后剩下的节点为赫夫曼树的根节点
        return nodes.get(0);
    }

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

}


class Node implements Comparable<Node> {
    Byte data;//存放数据本身，比如'a'->97
    int weight;//权值，表示字符出现的次数
    Node left;
    Node right;

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

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

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

    //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();
        }
    }
}