Metadata.java #3

/**
 * Copyright (c) 2010 Perforce Software. All rights reserved.
 */
package com.perforce.maven.mojo;

import java.io.InputStream;
import java.net.URL;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.util.jar.Manifest;

/**
 * Prints information from the JAR file's manifest.
 */
public class Metadata
{

    /**
     * Public main method, used solely for allowing customers to print version and other metadata information from the
     * enclosing JAR file's manifest. This information is printed to stdout; errors are printed to stderr.
     * 
     * @param args not used.
     */
    public static void main( String[] args )
    {
        try
        {
            Manifest manifest = getManifest();
            Attributes attr = manifest.getMainAttributes();
            System.out.println( attr.getValue( Name.IMPLEMENTATION_TITLE ) );
            StringBuilder version = new StringBuilder( attr.getValue( Name.IMPLEMENTATION_VERSION ) );
            // String changelist = attr.getValue("Build-Changelist");
            // if (changelist != null) {
            // version.append('/').append(changelist);
            // }
            // String type = attr.getValue("Build-Type");
            // if (type != null) {
            // version.append('/').append(type);
            // }
            System.out.println( version );
        }
        catch ( Exception exception )
        {
            System.err.println( exception.getLocalizedMessage() );
        }
    }

    /**
     * Get the JAR Manifest associated with this class instance, if it exists. The interpretation of the attributes in
     * this manifest is not defined here and will depend on how the jar was built; for a full list of normal Perforce
     * release build attributes, contact support, but in general, most of the normal Maven build attributes will
     * probably exist, as will Name.IMPLEMENTATION_TITLE and Name.IMPLEMENTATION_VERSION (but this is not guaranteed).
     * 
     * @return non-null Manifest object if it exists and is retrievable.
     * @throws Exception if the manifest can't be found or retrieved for any reason.
     */

    public static Manifest getManifest()
        throws Exception
    {
        String className = Metadata.class.getSimpleName() + ".class";
        URL classURL = Metadata.class.getResource( className );
        if ( classURL == null )
        {
            throw new Exception( "Error retrieving class as resource: " + className );
        }

        String classPath = classURL.toString();
        if ( !classPath.startsWith( "jar" ) )
        {
            throw new Exception( "Not running from jar file: " + classPath );
        }

        int separator = classPath.lastIndexOf( '!' );
        if ( separator != -1 && separator + 1 >= classPath.length() )
        {
            throw new Exception( "Invalid jar file class path: " + classPath );
        }

        String manifestPath = classPath.substring( 0, separator + 1 ) + "/META-INF/MANIFEST.MF";

        InputStream inStream = null;
        try
        {
            inStream = new URL( manifestPath ).openStream();
            return new Manifest( inStream );
        }
        finally
        {
            if ( inStream != null )
            {
                inStream.close();
            }
        }
    }
}