哈夫曼译码器java_哈夫曼编码译码器及代码

哈夫曼编码是一种压缩算法，可以将一个长的消息或文件压缩成较短的二进制码。哈夫曼编码通过构建一棵二叉树来生成编码，每个字符对应树上的一个叶子节点，该字符的编码是从根节点到叶子节点的路径上的0和1序列。

哈夫曼编码译码器的实现需要以下步骤：

1. 解析压缩文件中的哈夫曼编码表，生成哈夫曼树。
2. 读取压缩文件，并将二进制码转换为字符。
3. 使用哈夫曼树解码字符并输出原始消息或文件。

以下是一个Java实现的哈夫曼编码译码器的代码示例：

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

public class HuffmanDecoder {
    private Map<String, String> huffmanTable;

    public void decodeFile(String compressedFile, String outputFile) throws IOException {
        // 读取压缩文件
        byte[] compressedBytes = readCompressedFile(compressedFile);

        // 解析哈夫曼编码表
        huffmanTable = parseHuffmanTable(compressedBytes);

        // 构建哈夫曼树
        Node rootNode = buildHuffmanTree(huffmanTable);

        // 解码文件
        decodeBytes(compressedBytes, rootNode, outputFile);
    }

    private byte[] readCompressedFile(String compressedFile) throws IOException {
        FileInputStream inputStream = new FileInputStream(compressedFile);
        byte[] bytes = new byte[(int) new File(compressedFile).length()];
        inputStream.read(bytes);
        inputStream.close();
        return bytes;
    }

    private Map<String, String> parseHuffmanTable(byte[] compressedBytes) {
        Map<String, String> huffmanTable = new HashMap<String, String>();
        String tableString = new String(compressedBytes).split("\\|")[0];
        String[] entries = tableString.split(";");
        for (String entry : entries) {
            String[] parts = entry.split(":");
            huffmanTable.put(parts[0], parts[1]);
        }
        return huffmanTable;
    }

    private Node buildHuffmanTree(Map<String, String> huffmanTable) {
        List<Node> nodeList = new ArrayList<Node>();
        for (Map.Entry<String, String> entry : huffmanTable.entrySet()) {
            Node node = new Node(entry.getKey(), Integer.parseInt(entry.getValue()));
            nodeList.add(node);
        }
        while (nodeList.size() > 1) {
            Collections.sort(nodeList);
            Node leftChild = nodeList.remove(0);
            Node rightChild = nodeList.remove(0);
            Node parent = new Node(null, leftChild.frequency + rightChild.frequency);
            parent.leftChild = leftChild;
            parent.rightChild = rightChild;
            nodeList.add(parent);
        }
        return nodeList.get(0);
    }

    private void decodeBytes(byte[] compressedBytes, Node rootNode, String outputFile) throws IOException {
        StringBuilder binaryStringBuilder = new StringBuilder();
        for (int i = compressedBytes.length - 1; i >= 0; i--) {
            byte currentByte = compressedBytes[i];
            String binaryString = Integer.toBinaryString(currentByte & 255 | 256).substring(1);
            binaryStringBuilder.append(binaryString);
        }
        String binaryString = binaryStringBuilder.reverse().toString();

        FileOutputStream outputStream = new FileOutputStream(outputFile);
        Node currentNode = rootNode;
        for (int i = 0; i < binaryString.length(); i++) {
            if (binaryString.charAt(i) == '0') {
                currentNode = currentNode.leftChild;
            } else {
                currentNode = currentNode.rightChild;
            }
            if (currentNode.isLeaf()) {
                outputStream.write(currentNode.value.charAt(0));
                currentNode = rootNode;
            }
        }
        outputStream.close();
    }

    private class Node implements Comparable<Node> {
        private String value;
        private int frequency;
        private Node leftChild;
        private Node rightChild;

        public Node(String value, int frequency) {
            this.value = value;
            this.frequency = frequency;
        }

        public boolean isLeaf() {
            return leftChild == null && rightChild == null;
        }

        public int compareTo(Node other) {
            return frequency - other.frequency;
        }
    }

    public static void main(String[] args) throws IOException {
        HuffmanDecoder decoder = new HuffmanDecoder();
        decoder.decodeFile("compressed_file.bin", "output_file.txt");
    }
}

此代码解析压缩文件并生成哈夫曼树，然后使用该树来解码文件。要使用此代码，请将 `compressed_file.bin` 替换为要解码的文件名，将 `output_file.txt` 替换为输出文件名。