reading MANIFEST.MF file from jar file using JAVA

Question

Is there any way i can read the contents of a jar file. like i want to read the manifest file in order to find the creator of the jar file and version. Is there any way to a

Answer 1

I implemented an AppVersion class according to some ideas from stackoverflow, here I just share the entire class:

import java.io.File;
import java.net.URL;
import java.util.jar.Attributes;
import java.util.jar.Manifest;

import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class AppVersion {
  private static final Logger log = LoggerFactory.getLogger(AppVersion.class);

  private static String version;

  public static String get() {
    if (StringUtils.isBlank(version)) {
      Class<?> clazz = AppVersion.class;
      String className = clazz.getSimpleName() + ".class";
      String classPath = clazz.getResource(className).toString();
      if (!classPath.startsWith("jar")) {
        // Class not from JAR
        String relativePath = clazz.getName().replace('.', File.separatorChar) + ".class";
        String classFolder = classPath.substring(0, classPath.length() - relativePath.length() - 1);
        String manifestPath = classFolder + "/META-INF/MANIFEST.MF";
        log.debug("manifestPath={}", manifestPath);
        version = readVersionFrom(manifestPath);
      } else {
        String manifestPath = classPath.substring(0, classPath.lastIndexOf("!") + 1) + "/META-INF/MANIFEST.MF";
        log.debug("manifestPath={}", manifestPath);
        version = readVersionFrom(manifestPath);
      }
    }
    return version;
  }

  private static String readVersionFrom(String manifestPath) {
    Manifest manifest = null;
    try {
      manifest = new Manifest(new URL(manifestPath).openStream());
      Attributes attrs = manifest.getMainAttributes();

      String implementationVersion = attrs.getValue("Implementation-Version");
      implementationVersion = StringUtils.replace(implementationVersion, "-SNAPSHOT", "");
      log.debug("Read Implementation-Version: {}", implementationVersion);

      String implementationBuild = attrs.getValue("Implementation-Build");
      log.debug("Read Implementation-Build: {}", implementationBuild);

      String version = implementationVersion;
      if (StringUtils.isNotBlank(implementationBuild)) {
        version = StringUtils.join(new String[] { implementationVersion, implementationBuild }, '.');
      }
      return version;
    } catch (Exception e) {
      log.error(e.getMessage(), e);
    }
    return StringUtils.EMPTY;
  }
}

Basically, this class can read version information from the manifest of its own JAR file, or the manifest in it's classes folder. And hopefully it works on different platforms, but I only tested it on Mac OS X so far.

I hope this would be useful for someone else.

Answer 2

1. read version;
2. we copied MANIFEST.MF from jar to user home.

    public void processManifestFile() {
        String version = this.getClass().getPackage().getImplementationVersion();
        LOG.info("Version: {}", version);
        Path targetFile = Paths.get(System.getProperty("user.home"), "my-project", "MANIFEST.MF");

        try {
            URL url = this.getClass().getProtectionDomain().getCodeSource().getLocation();
            JarFile jarFile = new JarFile(url.getFile());
            Manifest manifest = jarFile.getManifest();
            try(FileWriter fw = new FileWriter(targetFile.toFile())) {
                manifest.getMainAttributes().entrySet().stream().forEach( x -> {
                    try {
                        fw.write(x.getKey() + ": " + x.getValue() + "\n");
                        LOG.info("{}: {}", x.getKey(), x.getValue());
                    } catch (IOException e) {
                        LOG.error("error in write manifest, {}", e.getMessage());
                    }
                });
            }
            LOG.info("Copy MANIFEST.MF to {}", targetFile);
        } catch (Exception e) {
            LOG.error("Error in processing MANIFEST.MF file", e);
        }
    }