Java壓縮技術（一） ZLib

有關ZLib可參見官方主頁 http://www.zlib.net/ 
ZLib可以簡單的理解爲壓縮/解壓縮算法，它與ZIP、RAR等歸檔算法有所不同，與bzip2比較接近。 

壓縮工具代碼如下： 

/**
 * 2009-9-9
 */
package org.zlex.commons.io;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.Inflater;
import java.util.zip.InflaterInputStream;

/**
 * ZLib壓縮工具
 *
 * @author <a href="mailto:[email protected]">樑棟</a>
 * @version 1.0
 * @since 1.0
 */
public abstract class ZLibUtils {

    /**
     * 壓縮
     *
     * @param data
     *            待壓縮數據
     * @return byte[] 壓縮後的數據
     */
    public static byte[] compress(byte[] data) {
        byte[] output = new byte[0];

        Deflater compresser = new Deflater();

        compresser.reset();
        compresser.setInput(data);
        compresser.finish();
        ByteArrayOutputStream bos = new ByteArrayOutputStream(data.length);
        try {
            byte[] buf = new byte[1024];
            while (!compresser.finished()) {
                int i = compresser.deflate(buf);
                bos.write(buf, 0, i);
            }
            output = bos.toByteArray();
        } catch (Exception e) {
            output = data;
            e.printStackTrace();
        } finally {
            try {
                bos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        compresser.end();
        return output;
    }

    /**
     * 壓縮
     *
     * @param data
     *            待壓縮數據
     *
     * @param os
     *            輸出流
     */
    public static void compress(byte[] data, OutputStream os) {
        DeflaterOutputStream dos = new DeflaterOutputStream(os);

        try {
            dos.write(data, 0, data.length);

            dos.finish();

            dos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 解壓縮
     *
     * @param data
     *            待壓縮的數據
     * @return byte[] 解壓縮後的數據
     */
    public static byte[] decompress(byte[] data) {
        byte[] output = new byte[0];

        Inflater decompresser = new Inflater();
        decompresser.reset();
        decompresser.setInput(data);

        ByteArrayOutputStream o = new ByteArrayOutputStream(data.length);
        try {
            byte[] buf = new byte[1024];
            while (!decompresser.finished()) {
                int i = decompresser.inflate(buf);
                o.write(buf, 0, i);
            }
            output = o.toByteArray();
        } catch (Exception e) {
            output = data;
            e.printStackTrace();
        } finally {
            try {
                o.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        decompresser.end();
        return output;
    }

    /**
     * 解壓縮
     *
     * @param is
     *            輸入流
     * @return byte[] 解壓縮後的數據
     */
    public static byte[] decompress(InputStream is) {
        InflaterInputStream iis = new InflaterInputStream(is);
        ByteArrayOutputStream o = new ByteArrayOutputStream(1024);
        try {
            int i = 1024;
            byte[] buf = new byte[i];

            while ((i = iis.read(buf, 0, i)) > 0) {
                o.write(buf, 0, i);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return o.toByteArray();
    }
}

測試用例代碼如下： 

/**
 * 2009-9-9
 */
package org.zlex.commons.io;

import static org.junit.Assert.*;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import org.junit.Test;

/**
 * ZLib壓縮測試用例
 *
 * @author <a href="mailto:[email protected]">樑棟</a>
 * @version 1.0
 * @since 1.0
 */
public class ZLibUtilsTest {

    @Test
    public final void testBytes() {
        System.err.println("字節壓縮／解壓縮測試");
        String inputStr = "[email protected];[email protected];[email protected]";
        System.err.println("輸入字符串:\t" + inputStr);
        byte[] input = inputStr.getBytes();
        System.err.println("輸入字節長度:\t" + input.length);

        byte[] data = ZLibUtils.compress(input);
        System.err.println("壓縮後字節長度:\t" + data.length);

        byte[] output = ZLibUtils.decompress(data);
        System.err.println("解壓縮後字節長度:\t" + output.length);
        String outputStr = new String(output);
        System.err.println("輸出字符串:\t" + outputStr);

        assertEquals(inputStr, outputStr);
    }

    @Test
    public final void testFile() {
        String filename = "zlib";
        File file = new File(filename);
        System.err.println("文件壓縮／解壓縮測試");
        String inputStr = "[email protected];[email protected];[email protected]";
        System.err.println("輸入字符串:\t" + inputStr);
        byte[] input = inputStr.getBytes();
        System.err.println("輸入字節長度:\t" + input.length);

        try {

            FileOutputStream fos = new FileOutputStream(file);
            ZLibUtils.compress(input, fos);
            fos.close();
            System.err.println("壓縮後字節長度:\t" + file.length());
        } catch (Exception e) {
            fail(e.getMessage());
        }

        byte[] output = null;

        try {
            FileInputStream fis = new FileInputStream(file);
            output = ZLibUtils.decompress(fis);
            fis.close();

        } catch (Exception e) {
            fail(e.getMessage());
        }
        System.err.println("解壓縮後字節長度:\t" + output.length);
        String outputStr = new String(output);
        System.err.println("輸出字符串:\t" + outputStr);

        assertEquals(inputStr, outputStr);
    }
}

輸入結果 

字節壓縮／解壓縮測試
輸入字符串:  [email protected];[email protected];[email protected]
輸入字節長度: 59
壓縮後字節長度:    39
解壓縮後字節長度:   59
輸出字符串:  [email protected];[email protected];[email protected]
文件壓縮／解壓縮測試
輸入字符串:  [email protected];[email protected];[email protected]
輸入字節長度: 59
壓縮後字節長度:    39
解壓縮後字節長度:   59
輸出字符串:  [email protected];[email protected];[email protected]

應該怎麼計算呢？原數據長度59字節，壓縮後39字節，大約是33％的壓縮率！ 

ZLib壓縮對大字節數據壓縮，才能反映出壓縮效果。 
先佔個位兒，回頭細緻整理！