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();
}
}
}
