how to check the version of jar file?

问题:

I am currently working on a J2ME polish application, just enhancing it. I am finding difficulties to get the exact version of the jar file. Is there any way to find the version of the jar file for the imports done in the class? I mean if you have some thing, import x.y.z; can we know the version of the jar x.y package belongs to?

回答1:

Decompress the JAR file and look for the manifest file (META-INF\MANIFEST.MF). The manifest file of JAR file might contain a version number (but not always a version is specified).

回答2:

You need to unzip it and check its META-INF/MANIFEST.MF file, e.g.

unzip -p file.jar | head

or more specific:

unzip -p file.jar META-INF/MANIFEST.MF

回答3:

Just to expand on the answers above, inside the META-INF/MANIFEST.MF file in the JAR, you will likely see a line: Manifest-Version: 1.0 ← This is NOT the jar versions number!

You need to look for Implementation-Version which, if present, is a free-text string so entirely up to the JAR's author as to what you'll find in there. See also Oracle docs and Package Version specificaion

回答4:

Just to complete the above answer.

Manifest file is located inside jar at META-INF\MANIFEST.MF path.

You can examine jar's contents in any archiver that supports zip.

回答5:

Each jar version has a unique checksum. You can calculate the checksum for you jar (that had no version info) and compare it with the different versions of the jar. We can also search a jar using checksum.

Refer this Question to calculate checksum: What is the best way to calculate a checksum for a file that is on my machine?

回答6:

Basically you should use the java.lang.Package class which use the classloader to give you informations about your classes.

example:

String.class.getPackage().getImplementationVersion();
Package.getPackage(this).getImplementationVersion();
Package.getPackage("java.lang.String").getImplementationVersion();

I think logback is known to use this feature to trace the JAR name/version of each class in its produced stacktraces.

see also http://docs.oracle.com/javase/8/docs/technotes/guides/versioning/spec/versioning2.html#wp90779

回答7:

This simple program will list all the cases for version of jar namely

• Version found in Manifest file
• No version found in Manifest and even from jar name

• Manifest file not found

  Map<String, String> jarsWithVersionFound   = new LinkedHashMap<String, String>();
  List<String> jarsWithNoManifest     = new LinkedList<String>();
  List<String> jarsWithNoVersionFound = new LinkedList<String>();
  
  //loop through the files in lib folder
  //pick a jar one by one and getVersion()
  //print in console..save to file(?)..maybe later
  
  File[] files = new File("path_to_jar_folder").listFiles();
  
  for(File file : files)
  {
      String fileName = file.getName();
  
  
      try
      {
          String jarVersion = new Jar(file).getVersion();
  
          if(jarVersion == null)
              jarsWithNoVersionFound.add(fileName);
          else
              jarsWithVersionFound.put(fileName, jarVersion);
  
      }
      catch(Exception ex)
      {
          jarsWithNoManifest.add(fileName);
      }
  }
  
  System.out.println("******* JARs with versions found *******");
  for(Entry<String, String> jarName : jarsWithVersionFound.entrySet())
      System.out.println(jarName.getKey() + " : " + jarName.getValue());
  
  System.out.println("\n \n ******* JARs with no versions found *******");
  for(String jarName : jarsWithNoVersionFound)
      System.out.println(jarName);
  
  System.out.println("\n \n ******* JARs with no manifest found *******");
  for(String jarName : jarsWithNoManifest)
      System.out.println(jarName);
  

It uses the javaxt-core jar which can be downloaded from http://www.javaxt.com/downloads/

回答8:

You can filter version from the MANIFEST file using

unzip -p my.jar META-INF/MANIFEST.MF | grep 'Bundle-Version'

回答9:

I'm late this but you can try the following two methods

using these needed classes

import java.util.jar.Attributes;
import java.util.jar.Manifest;

These methods let me access the jar attributes. I like being backwards compatible and use the latest. So I used this

public Attributes detectClassBuildInfoAttributes(Class sourceClass) throws MalformedURLException, IOException {
    String className = sourceClass.getSimpleName() + ".class";
    String classPath = sourceClass.getResource(className).toString();
    if (!classPath.startsWith("jar")) {
      // Class not from JAR
      return null;
    }
    String manifestPath = classPath.substring(0, classPath.lastIndexOf("!") + 1) + 
        "/META-INF/MANIFEST.MF";
    Manifest manifest = new Manifest(new URL(manifestPath).openStream());
    return manifest.getEntries().get("Build-Info");
}

public String retrieveClassInfoAttribute(Class sourceClass, String attributeName) throws MalformedURLException, IOException {
    Attributes version_attr = detectClassBuildInfoAttributes(sourceClass);

    String attribute = version_attr.getValue(attributeName);

    return attribute;
}

This works well when you are using maven and need pom details for know classes. Hope this helps.

回答10:

It can be checked with a command java -jar jarname