用java语言实现Huffman压缩与解压缩文件

好的，我可以为您提供Huffman压缩与解压缩文件的Java代码。以下是实现的步骤：

## Huffman压缩

1. 读取文件并统计每个字符出现的频率
2. 用字符频率构建Huffman树
3. 遍历Huffman树并生成每个字符的编码
4. 将编码写入输出文件，并将Huffman树写入输出文件
5. 关闭输入输出流

import java.io.*;

public class HuffmanCompression {

    private static final int BYTE_SIZE = 8;

    public static void compress(String inputFile, String outputFile) throws IOException {
        FileInputStream inputStream = new FileInputStream(inputFile);
        int[] frequencies = new int[256];
        int totalChars = 0;
        int nextByte = inputStream.read();
        while (nextByte != -1) {
            frequencies[nextByte]++;
            totalChars++;
            nextByte = inputStream.read();
        }
        inputStream.close();

        HuffmanNode root = buildHuffmanTree(frequencies);
        String[] codes = buildCodes(root);

        FileOutputStream outputStream = new FileOutputStream(outputFile);
        writeHeader(outputStream, frequencies);
        writeCompressedData(inputStream, outputStream, codes);
        outputStream.close();
    }

    private static HuffmanNode buildHuffmanTree(int[] frequencies) {
        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (int i = 0; i < frequencies.length; i++) {
            if (frequencies[i] > 0) {
                pq.add(new HuffmanNode((byte) i, frequencies[i]));
            }
        }

        while (pq.size() > 1) {
            HuffmanNode left = pq.poll();
            HuffmanNode right = pq.poll();
            HuffmanNode parent = new HuffmanNode(left, right);
            pq.add(parent);
        }

        return pq.poll();
    }

    private static String[] buildCodes(HuffmanNode root) {
        String[] codes = new String[256];
        buildCodesHelper(codes, root, "");
        return codes;
    }

    private static void buildCodesHelper(String[] codes, HuffmanNode node, String code) {
        if (node.isLeaf()) {
            codes[node.getByte()] = code;
        } else {
            buildCodesHelper(codes, node.getLeft(), code + "0");
            buildCodesHelper(codes, node.getRight(), code + "1");
        }
    }

    private static void writeHeader(FileOutputStream outputStream, int[] frequencies) throws IOException {
        for (int i = 0; i < frequencies.length; i++) {
            outputStream.write(frequencies[i]);
        }
    }

    private static void writeCompressedData(FileInputStream inputStream, FileOutputStream outputStream, String[] codes) throws IOException {
        int currentByte = 0;
        int numBits = 0;
        int nextByte = inputStream.read();
        while (nextByte != -1) {
            String code = codes[nextByte];
            for (int i = 0; i < code.length(); i++) {
                currentByte = currentByte << 1;
                if (code.charAt(i) == '1') {
                    currentByte |= 1;
                }
                numBits++;
                if (numBits == BYTE_SIZE) {
                    outputStream.write(currentByte);
                    currentByte = 0;
                    numBits = 0;
                }
            }
            nextByte = inputStream.read();
        }

        if (numBits > 0) {
            currentByte = currentByte << (BYTE_SIZE - numBits);
            outputStream.write(currentByte);
        }
    }

    private static class HuffmanNode implements Comparable<HuffmanNode> {
        private byte b;
        private int frequency;
        private HuffmanNode left;
        private HuffmanNode right;

        public HuffmanNode(byte b, int frequency) {
            this.b = b;
            this.frequency = frequency;
        }

        public HuffmanNode(HuffmanNode left, HuffmanNode right) {
            this.frequency = left.frequency + right.frequency;
            this.left = left;
            this.right = right;
        }

        public int getByte() {
            return b & 0xff;
        }

        public int getFrequency() {
            return frequency;
        }

        public boolean isLeaf() {
            return left == null && right == null;
        }

        public HuffmanNode getLeft() {
            return left;
        }

        public HuffmanNode getRight() {
            return right;
        }

        @Override
        public int compareTo(HuffmanNode o) {
            return Integer.compare(this.frequency, o.frequency);
        }
    }
}

## Huffman解压缩

1. 读取文件头并构建Huffman树
2. 读取压缩数据，并根据Huffman树解码
3. 将解码后的数据写入输出文件
4. 关闭输入输出流

import java.io.*;

public class HuffmanDecompression {

    private static final int BYTE_SIZE = 8;

    public static void decompress(String inputFile, String outputFile) throws IOException {
        FileInputStream inputStream = new FileInputStream(inputFile);
        int[] frequencies = new int[256];
        for (int i = 0; i < frequencies.length; i++) {
            frequencies[i] = inputStream.read();
        }

        HuffmanNode root = buildHuffmanTree(frequencies);
        int totalChars = root.getFrequency();

        FileOutputStream outputStream = new FileOutputStream(outputFile);
        int numBits = 0;
        int currentByte = 0;
        HuffmanNode node = root;
        int nextByte = inputStream.read();
        while (nextByte != -1) {
            for (int i = 0; i < BYTE_SIZE; i++) {
                int bit = (nextByte >> (BYTE_SIZE - 1 - i)) & 1;
                if (bit == 0) {
                    node = node.getLeft();
                } else {
                    node = node.getRight();
                }
                if (node.isLeaf()) {
                    outputStream.write(node.getByte());
                    node = root;
                    totalChars--;
                    if (totalChars == 0) {
                        break;
                    }
                }
            }
            nextByte = inputStream.read();
        }

        inputStream.close();
        outputStream.close();
    }

    private static HuffmanNode buildHuffmanTree(int[] frequencies) {
        PriorityQueue<HuffmanNode> pq = new PriorityQueue<>();
        for (int i = 0; i < frequencies.length; i++) {
            if (frequencies[i] > 0) {
                pq.add(new HuffmanNode((byte) i, frequencies[i]));
            }
        }

        while (pq.size() > 1) {
            HuffmanNode left = pq.poll();
            HuffmanNode right = pq.poll();
            HuffmanNode parent = new HuffmanNode(left, right);
            pq.add(parent);
        }

        return pq.poll();
    }

    private static class HuffmanNode implements Comparable<HuffmanNode> {
        private byte b;
        private int frequency;
        private HuffmanNode left;
        private HuffmanNode right;

        public HuffmanNode(byte b, int frequency) {
            this.b = b;
            this.frequency = frequency;
        }

        public HuffmanNode(HuffmanNode left, HuffmanNode right) {
            this.frequency = left.frequency + right.frequency;
            this.left = left;
            this.right = right;
        }

        public int getByte() {
            return b & 0xff;
        }

        public int getFrequency() {
            return frequency;
        }

        public boolean isLeaf() {
            return left == null && right == null;
        }

        public HuffmanNode getLeft() {
            return left;
        }

        public HuffmanNode getRight() {
            return right;
        }

        @Override
        public int compareTo(HuffmanNode o) {
            return Integer.compare(this.frequency, o.frequency);
        }
    }
}

以上就是Huffman压缩与解压缩文件的Java代码，您可以根据您的需要进行修改和优化。