Compress and Decompress Java JAR File with Apache Compress

In this tutorial we demonstrate how to compress and decompress Java JAR files using Apache Compress. In general, JAR archives are ZIP files, so the JAR package supports all options provided by the ZIP package.

Project Structure

Let’s start by looking at the project structure.

Maven Dependencies

We use Apache Maven to manage our project dependencies. Make sure the following dependencies reside on the class-path. We use Apache Commons Compress, make sure the org.apache.commons:commons-compress dependency resides on the class-path.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.memorynotfound.io.compression</groupId>
    <artifactId>jar</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <name>IO Compression - ${project.artifactId}</name>
    <url>https://memorynotfound.com</url>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-compress</artifactId>
            <version>1.14</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

Compress and Decompress Java JAR File with Apache Compress

JAR archives are ZIP files, so the JAR package supports all options provided by the ZIP package. To be interoperable JAR archives should always be created using the UTF-8 encoding for file names (which is the default).

• Compressing files in JAR format: We use the JarArchiveOutputStream to compress files and/or directories into JAR format. We can add entries in the archive using the JarArchiveOutputStream.putArchiveEntry method and pass in a JarArchiveEntry as an argument containing the file and filename respectively..
• Decompressing JAR archive: We can decompress the JAR archive using the JarArchiveInputStream class. Next, we loop over the JarArchiveEntry using the JarArchiveEntry.getNextJarEntry() class and copy the content to an FileOutputStream.

Archives created using JarArchiveOutputStream will implicitly add a JarMaker extra field to the very first archive entry of the archive which will make Solaris recognize them as Java archives and allows them to be used as executables.

package com.memorynotfound.resource;

import org.apache.commons.compress.archivers.jar.JarArchiveEntry;
import org.apache.commons.compress.archivers.jar.JarArchiveInputStream;
import org.apache.commons.compress.archivers.jar.JarArchiveOutputStream;
import org.apache.commons.compress.utils.IOUtils;

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

public class JAR {

    private JAR() {}

    public static void compress(String name, File... files) throws IOException {
        try (JarArchiveOutputStream out = new JarArchiveOutputStream(new FileOutputStream(name))){
            for (File file : files){
                addToArchiveCompression(out, file, ".");
            }
        }
    }

    public static void decompress(String in, File destination) throws IOException {
        try (JarArchiveInputStream jin = new JarArchiveInputStream(new FileInputStream(in))){
            JarArchiveEntry entry;
            while ((entry = jin.getNextJarEntry()) != null) {
                if (entry.isDirectory()){
                    continue;
                }
                File curfile = new File(destination, entry.getName());
                File parent = curfile.getParentFile();
                if (!parent.exists()) {
                    if (!parent.mkdirs()){
                        throw new RuntimeException("could not create directory: " + parent.getPath());
                    }
                }
                IOUtils.copy(jin, new FileOutputStream(curfile));
            }
        }
    }

    private static void addToArchiveCompression(JarArchiveOutputStream out, File file, String dir) throws IOException {
        String name = dir + File.separator + file.getName();
        if (file.isFile()){
            JarArchiveEntry entry = new JarArchiveEntry(name);
            out.putArchiveEntry(entry);
            entry.setSize(file.length());
            IOUtils.copy(new FileInputStream(file), out);
            out.closeArchiveEntry();
        } else if (file.isDirectory()) {
            File[] children = file.listFiles();
            if (children != null){
                for (File child : children){
                    addToArchiveCompression(out, child, name);
                }
            }
        } else {
            System.out.println(file.getName() + " is not supported");
        }
    }
}

Java JAR Example

This program demonstrates the JAR archive compression decompression example.

package com.memorynotfound.resource;

import java.io.File;
import java.io.IOException;

public class JARProgram {

    private static final String OUTPUT_DIRECTORY = "/tmp";
    private static final String TAR_GZIP_SUFFIX = ".jar";

    private static final String MULTIPLE_RESOURCES = "/example-multiple-resources";
    private static final String RECURSIVE_DIRECTORY = "/example-recursive-directory";

    private static final String MULTIPLE_RESOURCES_PATH = OUTPUT_DIRECTORY + MULTIPLE_RESOURCES + TAR_GZIP_SUFFIX;
    private static final String RECURSIVE_DIRECTORY_PATH = OUTPUT_DIRECTORY + RECURSIVE_DIRECTORY + TAR_GZIP_SUFFIX;


    public static void main(String... args) throws IOException {

        // class for resource classloading
        Class clazz = JARProgram.class;

        // get multiple resources files to compress
        File resource1 = new File(clazz.getResource("/in/resource1.txt").getFile());
        File resource2 = new File(clazz.getResource("/in/resource2.txt").getFile());
        File resource3 = new File(clazz.getResource("/in/resource3.txt").getFile());

        // compress multiple resources
        JAR.compress(MULTIPLE_RESOURCES_PATH, resource1, resource2, resource3);

        // decompress multiple resources
        JAR.decompress(MULTIPLE_RESOURCES_PATH, new File(OUTPUT_DIRECTORY + MULTIPLE_RESOURCES));



        // get directory file to compress
        File directory = new File(clazz.getResource("/in/dir").getFile());

        // compress recursive directory
        JAR.compress(RECURSIVE_DIRECTORY_PATH, directory);

        // decompress recursive directory
        JAR.decompress(RECURSIVE_DIRECTORY_PATH, new File(OUTPUT_DIRECTORY + RECURSIVE_DIRECTORY));
    }
}

Generated Files

Here is an example of the generated JAR archive.

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