decompress.java

利用霍夫曼树实现文本压缩。如果是文本可以压缩到40％的大小

package org.galaxy_OPEN.www.datastructures.huffman;

import java.io.*;

public class Decompress {
	private HuffmanFrame hfRef;

	private ObjectInputStream ois;

	private DataOutputStream dos;

	private FileHeader fileHeader;

	private Node huffTree;

	private long bytesWritten;

	private Node currentByteValue;

	private String outPath;

	private File tmpFile;

	public Decompress(HuffmanFrame hf, String inPath, String outPath)
			throws FileNotFoundException, IOException {
		hfRef = hf;
		bytesWritten = 0;
		this.outPath = outPath;
		tmpFile = new File(outPath);
		ois = new ObjectInputStream(new FileInputStream(inPath));
		dos = new DataOutputStream(new FileOutputStream(outPath));
	}

	private void readHeader() throws IOException, ClassNotFoundException {
		fileHeader = (FileHeader) ois.readObject();
		huffTree = fileHeader.getHuffmanTree();
		currentByteValue = huffTree;

		String name = fileHeader.getOriginalFileName();
		int extIndex = name.indexOf(".");
		String ext = name.substring(extIndex);
		if (dos != null) {
			dos.close();
		}
		if (tmpFile != null) {
			tmpFile.delete();
		}
		dos = new DataOutputStream(new FileOutputStream(outPath + ext));
	}

	private void decode(byte[] data) throws IOException {
		byte toWrite;
		int posi;

		for (int i = 0; i < data.length; i++) {
			byte leByte = data[i];
			for (int j = 7; j >= 0; j--) {
				if (((leByte >>> j) & 0x1) == 0)
					currentByteValue = currentByteValue.getLeftChild();
				else
					currentByteValue = currentByteValue.getRightChild();

				if (currentByteValue.isLeaf()) {
					posi = currentByteValue.getPosition();

					toWrite = (byte) (posi >= 128 ? posi - 256 : posi);
					dos.writeByte(toWrite); // On l'ecrit
					bytesWritten++;

					if (bytesWritten == fileHeader.getNumBytes())
						return;
					currentByteValue = huffTree;
				}
			}
		}
	}

	public void decode() throws IOException, ClassNotFoundException {
		hfRef.setMessage(hfRef.getFile().getPath() + " 正在解压缩……");
		byte[] data;

		readHeader();

		int numBytesLeft = ois.available();

		while (numBytesLeft > 0) {
			data = new byte[numBytesLeft];
			ois.read(data);
			decode(data);
			numBytesLeft = ois.available();
		}
		ois.close();
		dos.flush();
		dos.close();
		hfRef.setMessage(hfRef.getFile().getPath() + " 解压缩完成！");
	}
}