Java – Compress a file in Gzip format

By mkyong | Updated: August 13, 2020

Viewed: 11,302 (+151 pv/w)

Tags: compress file gzip java.io java.nio

This article shows how to use Java to compress a file in Gzip format.

1. What is Gzip?
GZip is a standard file compression tool on Unix or Linux system, and generally has the suffix .gz.

2. Why we need to compress a file in Gzip?
Answer: Smaller file size, save disk space.

3. How about tar.gz?
Gzip compress a single file, and the Tar is collecting files into one archive file, visit this article to Create tar.gz in Java

1. Compress a file in Gzip – GZIPOutputStream

We copy the FileInputStream into a GZIPOutputStream to compress a file in Gzip format.

1.1 The below example compresses a file sitemap.xml into a Gzip file sitemap.xml.gz.

package com.mkyong.io.howto.compress;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.zip.GZIPOutputStream;

public class GZipExample {

    public static void main(String[] args) {

        // compress a file
        Path source = Paths.get("/home/mkyong/test/sitemap.xml");
        Path target = Paths.get("/home/mkyong/test/sitemap.xml.gz");

        if (Files.notExists(source)) {
            System.err.printf("The path %s doesn't exist!", source);
            return;
        }

        try {

            GZipExample.compressGzip(source, target);

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

    }

    // copy file (FileInputStream) to GZIPOutputStream
    public static void compressGzip(Path source, Path target) throws IOException {

        try (GZIPOutputStream gos = new GZIPOutputStream(
                                      new FileOutputStream(target.toFile()));
             FileInputStream fis = new FileInputStream(source.toFile())) {

            // copy file
            byte[] buffer = new byte[1024];
            int len;
            while ((len = fis.read(buffer)) > 0) {
                gos.write(buffer, 0, len);
            }

        }

    }

}

Output, the XML file is compressed in Gzip format, and the file size drops from 388k to 40k.

$ ls -lsah sitemap.*
388K -rw-rw-r-- 1 mkyong mkyong 388K Ogos 12 14:02 sitemap.xml
 40K -rw-rw-r-- 1 mkyong mkyong  40K Ogos 12 14:06 sitemap.xml.gz


$ gzip -l sitemap.xml.gz
       compressed        uncompressed  ratio uncompressed_name
            40154              396719  89.9% sitemap.xml              

1.2 This example is similar to example 1.1. Instead, we use NIO Files.copy to copy a Path to GZIPOutputStream directly.

  public static void compressGzipNio(Path source, Path target) throws IOException {

      try (GZIPOutputStream gos = new GZIPOutputStream(
                                    new FileOutputStream(target.toFile()))) {

          Files.copy(source, gos);

      }

  }

2. Compress a String to Gzip

2.1 This example compresses a String into a Gzip file.

  public static void compressStringToGzip(String data, Path target) throws IOException {

      try (GZIPOutputStream gos = new GZIPOutputStream(
                                    new FileOutputStream(target.toFile()))) {

          gos.write(data.getBytes(StandardCharsets.UTF_8));

      }

  }

Download Source Code

References

• GZIPOutputStream JavaDoc
• Wikipedia – GZip
• gzip site
• GNU Gzip
• Gzip vs Zip
• Java – How to decompress a GZIP file
• Create tar.gz in Java