应好友需要，整理一下Java的压缩算法，先从ZLib开始。 相关链接： 有关ZLib可参见官方主页 ZLib可以简单的理解为压缩/解压缩算法，它与ZIP、RAR等归档算法有所不同，与bzip2比较接近。 压缩工具代码如下：

/** * 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压缩工具 *  * @author 梁栋 * @version 1.0 * @since 1.0 */public abstract class ZLibUtils {	/**	 * 压缩	 * 	 * @param data	 *            待压缩数据	 * @return byte[] 压缩后的数据	 */	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;	}	/**	 * 压缩	 * 	 * @param data	 *            待压缩数据	 * 	 * @param os	 *            输出流	 */	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();		}	}	/**	 * 解压缩	 * 	 * @param data	 *            待压缩的数据	 * @return byte[] 解压缩后的数据	 */	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;	}	/**	 * 解压缩	 * 	 * @param is	 *            输入流	 * @return byte[] 解压缩后的数据	 */	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();	}}

测试用例代码如下：

/** * 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压缩测试用例 *  * @author 梁栋 * @version 1.0 * @since 1.0 */public class ZLibUtilsTest {	@Test	public final void testBytes() {		System.err.println("字节压缩／解压缩测试");		String inputStr = "snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org";		System.err.println("输入字符串:\t" + inputStr);		byte[] input = inputStr.getBytes();		System.err.println("输入字节长度:\t" + input.length);		byte[] data = ZLibUtils.compress(input);		System.err.println("压缩后字节长度:\t" + data.length);		byte[] output = ZLibUtils.decompress(data);		System.err.println("解压缩后字节长度:\t" + output.length);		String outputStr = new String(output);		System.err.println("输出字符串:\t" + outputStr);		assertEquals(inputStr, outputStr);	}	@Test	public final void testFile() {		String filename = "zlib";		File file = new File(filename);		System.err.println("文件压缩／解压缩测试");		String inputStr = "snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org";		System.err.println("输入字符串:\t" + inputStr);		byte[] input = inputStr.getBytes();		System.err.println("输入字节长度:\t" + input.length);		try {			FileOutputStream fos = new FileOutputStream(file);			ZLibUtils.compress(input, fos);			fos.close();			System.err.println("压缩后字节长度:\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("解压缩后字节长度:\t" + output.length);		String outputStr = new String(output);		System.err.println("输出字符串:\t" + outputStr);		assertEquals(inputStr, outputStr);	}}

输入结果

字节压缩／解压缩测试输入字符串:	snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org输入字节长度:	59压缩后字节长度:	39解压缩后字节长度:	59输出字符串:	snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org文件压缩／解压缩测试输入字符串:	snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org输入字节长度:	59压缩后字节长度:	39解压缩后字节长度:	59输出字符串:	snowolf@zlex.org;dongliang@zlex.org;zlex.dongliang@zlex.org

应该怎么计算呢？原数据长度59字节，压缩后39字节，大约是33％的压缩率！ ZLib压缩对大字节数据压缩，才能反映出压缩效果。 先占个位儿，回头细致整理！