GZip是常用的无损压缩算法实现，在Linux中较为常见，像我们在Linux安装软件时，基本都是.tar.gz格式。.tar.gz格式文件需要先对目录内文件进行tar压缩，然后使用GZip进行压缩。

​  本文针对磁盘上和内存中两种方式进行压缩和解压演示，演示只针对一层目录结构进行，多层目录只需递归操作进行即可。

  · Maven依赖

<dependency><groupId>org.apache.commons</groupId><artifactId>commons-compress</artifactId><version>1.19</version>
</dependency>

  · 磁盘压缩和解压

  无特殊情况下，操作都是在磁盘上进行，将所有文件存放在某一目录中，然后对目录进行压缩，工具类代码如下：

package com.arhorchin.securitit.compress.gzip;import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Paths;import org.apache.commons.compress.archivers.tar.TarArchiveEntry;
import org.apache.commons.compress.archivers.tar.TarArchiveInputStream;
import org.apache.commons.compress.archivers.tar.TarArchiveOutputStream;
import org.apache.commons.compress.compressors.gzip.GzipCompressorInputStream;
import org.apache.commons.compress.compressors.gzip.GzipCompressorOutputStream;public class GZipDiskUtil {/*** UTF-8字符集.*/public static String UTF8_CHARSET = "UTF-8";/*** tar打包压缩.* @param srcDirPath 原路径.* @param tarFilePath 目标路径.* @return 压缩结果.* @throws Exception .*/public static boolean tarCompress(String srcDirPath, String tarFilePath) throws Exception {FileOutputStream fos = null;TarArchiveOutputStream taos = null;File filePathFile = null;try {fos = new FileOutputStream(new File(tarFilePath));taos = new TarArchiveOutputStream(fos);filePathFile = new File(srcDirPath);for (File file : filePathFile.listFiles()) {BufferedInputStream bis = null;FileInputStream fis = null;try {TarArchiveEntry tae = new TarArchiveEntry(file);tae.setName(new String(file.getName().getBytes(UTF8_CHARSET), UTF8_CHARSET));taos.putArchiveEntry(tae);fis = new FileInputStream(file);bis = new BufferedInputStream(fis);int count;byte data[] = new byte[1024];while ((count = bis.read(data, 0, 1024)) != -1) {taos.write(data, 0, count);}} finally {taos.closeArchiveEntry();if (bis != null)bis.close();if (fis != null)fis.close();}}} finally {if (taos != null)taos.close();if (fos != null)fos.close();}return true;}/*** tar拆包解压.* @param srcFilePath 原路径.* @param targDirPath 目标路径.* @return 解压结果.* @throws Exception .*/public static boolean tarDecompress(String srcFilePath, String targDirPath) throws Exception {TarArchiveInputStream tais = null;FileInputStream fis = null;try {File file = new File(srcFilePath);fis = new FileInputStream(file);tais = new TarArchiveInputStream(fis);TarArchiveEntry tae = null;while ((tae = tais.getNextTarEntry()) != null) {BufferedOutputStream bos = null;FileOutputStream fos = null;try {String dir = targDirPath + File.separator + tae.getName();File dirFile = new File(dir);fos = new FileOutputStream(dirFile);bos = new BufferedOutputStream(fos);int count;byte data[] = new byte[1024];while ((count = tais.read(data, 0, 1024)) != -1) {bos.write(data, 0, count);}} finally {if (bos != null)bos.close();if (fos != null)fos.close();}}} finally {if (tais != null)tais.close();if (fis != null)fis.close();}return true;}/*** gzip压缩.* @param srcFilePath 原路径.* @param tarFilePath 目标路径.* @return 压缩结果.* @throws IOException .*/public static boolean gzipCompress(String srcFilePath, String tarFilePath) throws IOException {InputStream fin = null;BufferedInputStream bis = null;FileOutputStream fos = null;BufferedOutputStream bos = null;GzipCompressorOutputStream gcos = null;try {fin = Files.newInputStream(Paths.get(srcFilePath));bis = new BufferedInputStream(fin);fos = new FileOutputStream(tarFilePath);bos = new BufferedOutputStream(fos);gcos = new GzipCompressorOutputStream(bos);byte[] buffer = new byte[1024];int read = -1;while ((read = bis.read(buffer)) != -1) {gcos.write(buffer, 0, read);}} finally {if (gcos != null)gcos.close();if (bos != null)bos.close();if (fos != null)fos.close();if (bis != null)bis.close();if (fin != null)fin.close();}return true;}/*** gzip解压.* @param srcFilePath 原路径.* @param tarFilePath 目标路径.* @return 解压结果.* @throws IOException .*/public static boolean gzipDecompress(String srcFilePath, String tarFilePath) throws IOException {InputStream fin = null;BufferedInputStream in = null;OutputStream out = null;GzipCompressorInputStream gcis = null;try {out = Files.newOutputStream(Paths.get(tarFilePath));fin = Files.newInputStream(Paths.get(srcFilePath));in = new BufferedInputStream(fin);gcis = new GzipCompressorInputStream(in);final byte[] buffer = new byte[1024];int n = 0;while (-1 != (n = gcis.read(buffer))) {out.write(buffer, 0, n);}} finally {if (gcis != null)gcis.close();if (in != null)in.close();if (fin != null)fin.close();if (out != null)out.close();}return true;}}

​ 测试代码如下：

package com.arhorchin.securitit.com.compress;import com.arhorchin.securitit.compress.gzip.GZipDiskUtil;public class GZipDiskUtilTester {public static void main(String[] args) throws Exception {GZipDiskUtil.tarCompress("C:/Users/Administrator/Downloads/个人文件/2020-07-13/files", "C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk.tar");GZipDiskUtil.gzipCompress("C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk.tar", "C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk.tar.gz");GZipDiskUtil.gzipDecompress("C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk.tar.gz", "C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk-untar.tar");GZipDiskUtil.tarDecompress("C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk-untar.tar", "C:/Users/Administrator/Downloads/个人文件/2020-07-13/disk-untar");}}

  · 内存压缩和解压

  在实际应用中，对应不同需求，可能需要生成若干文件，然后将其压缩。在某些应用中，文件较小、文件数量较少且较为固定，频繁与磁盘操作，会带来不必要的效率影响。此时，可以在内存中将文件进行压缩得到.tar.gzip文件，工具类代码如下：

package com.arhorchin.securitit.compress.gzip;import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;import org.apache.commons.compress.archivers.tar.TarArchiveEntry;
import org.apache.commons.compress.archivers.tar.TarArchiveInputStream;
import org.apache.commons.compress.archivers.tar.TarArchiveOutputStream;
import org.apache.commons.compress.compressors.gzip.GzipCompressorInputStream;
import org.apache.commons.compress.compressors.gzip.GzipCompressorOutputStream;public class GZipMemoryUtil {/*** tar压缩.* @param fileBytesMap 待压缩文件集合.* @return tar文件内容.* @throws Exception .*/public static byte[] tarCompress(Map<String, byte[]> fileBytesMap) throws Exception {ByteArrayOutputStream tarBaos = null;TarArchiveOutputStream taos = null;try {tarBaos = new ByteArrayOutputStream();taos = new TarArchiveOutputStream(tarBaos);for (Map.Entry<String, byte[]> fileEntry : fileBytesMap.entrySet()) {TarArchiveEntry tae = new TarArchiveEntry(fileEntry.getKey());tae.setName(fileEntry.getKey());tae.setSize(fileEntry.getValue().length);taos.putArchiveEntry(tae);taos.write(fileEntry.getValue());taos.closeArchiveEntry();}} finally {if (taos != null) {taos.close();}}return tarBaos.toByteArray();}/*** tar解压.* @param fileBytes tar压缩文件内容.* @return 解压后文件集合.* @throws Exception .*/public static Map<String, byte[]> tarDecompress(byte[] fileBytes) throws Exception {Map<String, byte[]> fileBytesMap = null;TarArchiveInputStream tais = null;ByteArrayOutputStream taeBaos = null;try {fileBytesMap = new HashMap<String, byte[]>();tais = new TarArchiveInputStream(new ByteArrayInputStream(fileBytes));TarArchiveEntry tae = null;while ((tae = tais.getNextTarEntry()) != null) {taeBaos = new ByteArrayOutputStream();int count;byte data[] = new byte[1024];while ((count = tais.read(data, 0, 1024)) != -1) {taeBaos.write(data, 0, count);}fileBytesMap.put(tae.getName(), taeBaos.toByteArray());}} finally {if (tais != null)tais.close();}return fileBytesMap;}/*** gzip压缩.* @param fileBytes 待压缩文件.* @return 已压缩文件.* @throws IOException .*/public static byte[] gzipCompress(byte[] fileBytes) throws IOException {ByteArrayOutputStream gzipBaos = null;GzipCompressorOutputStream gcos = null;try {gzipBaos = new ByteArrayOutputStream();gcos = new GzipCompressorOutputStream(gzipBaos);gcos.write(fileBytes);} finally {if (gcos != null)gcos.close();}return gzipBaos.toByteArray();}/*** gzip解压.* @param fileBytes 待解压文件.* @return 已解压文件.* @throws IOException .*/public static byte[] gzipDecompress(byte[] fileBytes) throws IOException {ByteArrayOutputStream gzipBaos = null;ByteArrayInputStream gzipBais = null;GzipCompressorInputStream gcis = null;try {gzipBaos = new ByteArrayOutputStream();gzipBais = new ByteArrayInputStream(fileBytes);gcis = new GzipCompressorInputStream(gzipBais);final byte[] buffer = new byte[1024];int n = 0;while (-1 != (n = gcis.read(buffer))) {gzipBaos.write(buffer, 0, n);}} finally {if (gcis != null)gcis.close();}return gzipBaos.toByteArray();}}

  测试代码如下：

package com.arhorchin.securitit.com.compress;import java.io.File;
import java.util.HashMap;
import java.util.Map;import org.apache.commons.io.FileUtils;import com.arhorchin.securitit.compress.gzip.GZipMemoryUtil;public class GZipMemoryUtilTester {public static void main(String[] args) throws Exception {Map<String, byte[]> fileBytesMap = null;fileBytesMap = new HashMap<String, byte[]>();// 设置文件列表.File dirFile = new File("C:/Users/Administrator/Downloads/个人文件/2020-07-13/files");for (File file : dirFile.listFiles()) {fileBytesMap.put(file.getName(), FileUtils.readFileToByteArray(file));}byte[] memoryBytes = GZipMemoryUtil.tarCompress(fileBytesMap);memoryBytes = GZipMemoryUtil.gzipCompress(memoryBytes);FileUtils.writeByteArrayToFile(new File("C:/Users/Administrator/Downloads/个人文件/2020-07-13/memory.tar.gz"), memoryBytes);memoryBytes = GZipMemoryUtil.gzipDecompress(memoryBytes);fileBytesMap = GZipMemoryUtil.tarDecompress(memoryBytes);System.out.println(fileBytesMap.size());}}

  · 总结

  1) 在小文件、文件数量较小且较为固定时，提倡使用内存压缩和解压方式。使用内存换时间，减少频繁的磁盘操作。

  2) 在大文件、文件数量较大时，提倡使用磁盘压缩和解压方式。过大文件对服务会造成过度的负载，磁盘压缩和解压可以缓解这种压力。