Listing the Main Attributes in a JAR File Manifest

Jar Manifest: Jar Manifest file is the main section of a jar file. This file contains the detailed information about the specific individual jar file. It contains the complete information about the jar file, each and every section or particular information is separated by new line. For mentioning information in the manifest file you have to maintain the information syntax with rule and restrictions.

Main Attributes in Jar file are these attributes which are applied for each and every individual manifest file for entry. This section, in which these attributes are defined, contains jar configuration and security information. This section is terminated by new empty line.

An individual section of the manifest file contains the list of the information about packages and files which are to be signed. There not need to list all the files of the jar file. The manifest file itself not nee to be listed. Every section starts with the name of attributes and values of these attributes. Attributes and values are separated with colon (":"). Values of the attributes are mentioned according to the attributes like relative path to the path, an absolute URL for archiving data from outside.

Program Result:

Following program is given for the best illustration of the jar manifest file. This program takes a jar file which manifest file content has to be shown and helping you to show the main attributes and values of all attributes mentioned in the manifest file. It checks for the file format (for the jar format) and it also checks whether the file exists or not.

Here is the code of the program:


import java.util.*;

import java.util.jar.*;

import java.io.*;



public class MainJarAtr{

  public static void main(String[] args){

    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    try {

      System.out.print("Enter jar file name: ");

      String filename = in.readLine();

      if(!filename.endsWith(".jar")){

        System.out.println("File not in jar format.");

        System.exit(0);

      }



      File file = new File(filename);

      if (file.exists()){

        // Open the JAR file

        JarFile jarfile = new JarFile(filename);



        // Get the manifest

        Manifest manifest = jarfile.getManifest();



        // Get the main attributes in the manifest

        Attributes attrs = (Attributes)manifest.getMainAttributes();



        // Enumerate each attribute

        for (Iterator it=attrs.keySet().iterator(); it.hasNext(); ) {

          // Get attribute name

          Attributes.Name attrName = (Attributes.Name)it.next();

          System.out.print(attrName + ": ");

          

          // Get attribute value

          String attrValue = attrs.getValue(attrName);

          System.out.print(attrValue);

          System.out.println();

        }

      }

      else{

        System.out.print("File not found.");

        System.exit(0);

      }

    }

    catch (IOException e) {}

  }

}