Replacing the MANIFEST.MF file in a JAR programmatically

Question

I want to modify the MANIFEST.MF after creating the JAR to exclude certain Class-Path entries. For this I decided to use zip4j. Extraction seems to work fine but for putting the MANIFEST.MF file back into the JAR, I use the following code:

String metaInfFolderName = "META-INF";
Path extractedManifestFilePath = Paths.get("...");
ZipFile zipFile = new ZipFile("Test-Zip-File.zip");
ZipParameters zipParameters = new ZipParameters();
zipParameters.setDefaultFolderPath(metaInfFolderName);
zipFile.addFile(extractedManifestFilePath.toFile(), zipParameters);

However, this code does not work as expected: The parent directory always ends up being named NF instead of the full META-INF. It seems like the starting characters are cut off. What could be the reason for this or is there another meaningful possibility to replace files inside JARs (which are essentially just ZIPs)?

maven dependency:

<dependency>
    <groupId>net.lingala.zip4j</groupId>
    <artifactId>zip4j</artifactId>
    <version>2.6.1</version>
</dependency>

Furthermore I tried using the jar utility like described here but when invoking the command jar uf MyJAR.jar META-INF/MANIFEST.MF the MANIFEST.MF inside the JAR gets deleted instead of replaced. Using the zip utility via zip -ur MyJAR.jar "META-INF/MANIFEST.MF" works but corrupts the JAR file so it is no longer runnable:

Error: An unexpected error occurred while trying to open file MyJAR.jar

Puce · Accepted Answer · 2020-06-25T19:04:30.687

You can use something like this:

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.*;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.util.jar.Manifest;

public class ManifestManipulator {

    public static final void main(String... args) throws IOException {
        if (args.length == 0) {
            throw new IllegalArgumentException("at least the path to the JAR file expected!");
        }
        Path jarPath = Paths.get(args[0]);
        Set<String> attributeNames = args.length > 1 ? new LinkedHashSet<>(List.of(args).subList(1, args.length)) : Set.of();

        if (!attributeNames.isEmpty()) {
            ManifestManipulator manifestManipulator = new ManifestManipulator();
            manifestManipulator.removeManifestEntries(jarPath, attributeNames);
        } else {
            System.out.println("Warning: no entries specified to remove!");
        }
    }

    private void removeManifestEntries(Path jarPath, Set<String> attributeNames) throws IOException {
        System.out.println("Going to remove: " + attributeNames);
        try (FileSystem jarFS = FileSystems.newFileSystem(URI.create("jar:" + jarPath.toUri()), Map.of())) {
            Path manifestPath = jarFS.getPath("META-INF", "MANIFEST.MF");
            Manifest manifest = readManifest(manifestPath);
            Attributes mainAttributes = manifest.getMainAttributes();
            System.out.println("Found main attribute names: " + mainAttributes.keySet());

            boolean removed = mainAttributes.entrySet().removeIf(entry -> attributeNames.contains(((Name) entry.getKey()).toString()));
            if (removed) {
                writeManifest(manifestPath, manifest);
            } else {
                System.out.println("Warning: nothing removed");
            }
        }
    }

    private Manifest readManifest(Path manifestPath) throws IOException {
        try (InputStream is = Files.newInputStream(manifestPath)) {
            return new Manifest(is);
        }
    }

    private void writeManifest(Path manifestPath, Manifest manifest) throws IOException {
        try (OutputStream os = Files.newOutputStream(manifestPath)) {
            manifest.write(os);
        }
    }

}

Please make sure you've added the jdk.zipfs module, which will provide a FileSystemProvider for ZIP/JAR files (see the technote).

I'm actually still using `Java 8`, is your code or something similar still functional under that version? If not, it's also okay actually, I can certainly migrate to a newer Java version. — BullyWiiPlaza, Jun 22 '20 at 21:30
@BullyWiiPlaza It should also be working with Java 8 with some minor changes (replace List.of() with Arrays.asList() etc.). At least the Oracle JDK 8 has the ZIP/JAR FileSystemProvider already on the classpath out-of-the-box (so it's even simpler than with Java 11). — Puce, Jun 23 '20 at 06:27

score 2 · Answer 2 · answered Jun 25 '20 at 08:57

You do not need any external dependency to alter the content of a ZIP or JAR file with Java 8.

public static void main(String[] args) throws IOException {
    Path zipFilePath = Paths.get("path/to/my/app.jar");
    try (FileSystem zipFileSystem = FileSystems.newFileSystem(zipFilePath, null)) {
        Path manifestFile = zipFileSystem.getPath("META-INF/MANIFEST.MF");
        String newManifestContent;
        // Read from MANIFEST.MF.
        try (Stream<String> lines = Files.lines(manifestFile, StandardCharsets.UTF_8)) {
            newManifestContent = lines.filter(l -> !l.startsWith("Class-Path entry I want to remove"))
                    .collect(Collectors.joining("\n"));
        }
        // Replace MANIFEST.MF content.
        Files.write(manifestFile, newManifestContent.getBytes(StandardCharsets.UTF_8), StandardOpenOption.TRUNCATE_EXISTING);
    }
}

Replacing the MANIFEST.MF file in a JAR programmatically

2 Answers2