compress.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 Compress {
	private HuffmanFrame hfRef;

	private String[] tabCorresp;

	private DataInputStream dataInput;

	private String buffer;

	private ObjectOutputStream oos;

	private FileHeader fileHeader;

	private File outputFile;

	private long bitWritten;

	public Compress(HuffmanFrame hf, String inPath, String outPath)
			throws IOException {
		hfRef = hf;
		File inputFile = new File(inPath);
		outputFile = new File(outPath);

		Node[] tabFreq = loadFreqencyTable(inputFile);
		Node huffmanTree = buildHuffmanTree(tabFreq);
		tabCorresp = getCorresp(huffmanTree);

		ObjectOutputStream objOut = new ObjectOutputStream(
				new FileOutputStream(outputFile));
		FileHeader outputFileHeader = new FileHeader(inputFile.getName(),
				inputFile.length(), huffmanTree);
		dataInput = new DataInputStream(new FileInputStream(inputFile));

		buffer = "";
		oos = objOut;
		fileHeader = outputFileHeader;
	}

	public void encode() throws IOException {
		hfRef.setMessage("正在压缩……");
		encodeFile(dataInput, tabCorresp);
		hfRef.setMessage(hfRef.getFile().getPath() + " 压缩完成！");
	}

	public void encodeFile(DataInputStream dataInput, String[] corresp)
			throws IOException {
		byte[] data;

		writeHeader();

		int numBytesLeft = dataInput.available();
		while (numBytesLeft > 0) {
			data = new byte[numBytesLeft];
			dataInput.read(data);

			for (int i = 0; i < data.length; i++) {
				writeEncoded(convert(data[i], corresp));
			}

			numBytesLeft = dataInput.available();
		}

		writeEOF();
		dataInput.close();

		if (outputFile != null) {
			outputFile.setReadOnly();
		}
	}

	private static Node[] loadFreqencyTable(File inputFile) throws IOException {
		Node[] tabFreq = new Node[256];

		FrequencyTableLoader freqReader = new FrequencyTableLoader(inputFile);
		for (int i = 0; i < tabFreq.length; i++) {
			tabFreq[i] = new Node(i);
		}
		freqReader.loadFrequencyTable(tabFreq);
		return tabFreq;
	}

	private static Node buildHuffmanTree(Node[] tabFreq) {
		Heap priorityQ = new Heap(256);
		for (int i = 0; i < tabFreq.length; i++) {
			if (tabFreq[i].getFrequency() > 0)
				priorityQ.append(tabFreq[i]);
		}
		priorityQ.sort();

		while (priorityQ.getCurrentSize() >= 2) {
			Node temp = new Node();
			temp.setLeftChild(priorityQ.remove());
			temp.setRightChild(priorityQ.remove());
			temp.setFreq(temp.getRightChild().getFrequency()
					+ temp.getLeftChild().getFrequency());
			priorityQ.insertOrdered(temp);
		}

		Node huffmanTree = priorityQ.remove();

		priorityQ = null;
		return huffmanTree;
	}

	private static String[] getCorresp(Node huffmanTree) {
		TreeOps treeOps = new TreeOps();

		treeOps.loadLeavesCodes(huffmanTree);
		String[] tabCorresp = treeOps.getCorrespTable();

		treeOps = null;
		return tabCorresp;
	}

	private void writeHeader() throws IOException {
		oos.writeObject(fileHeader);
		oos.flush();
	}

	private void writeEncoded(String code) throws IOException {
		byte byteToWrite = 0;

		buffer += code;

		while (buffer.length() >= 8) {
			for (int i = 7; i >= 0; i--) {
				byteToWrite <<= 1;
				if (buffer.charAt(0) == '1')
					byteToWrite++;
				buffer = buffer.substring(1);
			}

			oos.writeByte(byteToWrite);
			byteToWrite = 0;
		}
	}

	private void writeEOF() throws IOException {
		byte finalByte = 0;

		for (int i = 7; i >= 0; i--) {
			finalByte <<= 1;

			if (buffer.length() > 0) {
				if (buffer.charAt(0) == '1')
					finalByte++;
				buffer = buffer.substring(1);
			}
		}

		oos.writeByte(finalByte);
		oos.flush();
		oos.close();

	}

	private String convert(byte info, String[] corresp) {
		int posi = (info < 0 ? info + 256 : info);
		return corresp[posi];
	}
}