Retrieve the Implementation-Version string from the Jar file that contains the specified Class. - Java Reflection

Java examples for Reflection:Jar

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Description

Retrieve the Implementation-Version string from the Jar file that contains the specified Class.

Demo Code

// Licensed under the Apache License, Version 2.0 (the "License");
import java.io.IOException;
import java.io.InputStream;
import java.net.JarURLConnection;
import java.net.URL;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Main{
    private static final Logger LOGGER = Logger.getLogger(JarUtils.class
            .getName());//w  ww.j  a v  a2 s  .c  o m
    /**
     * Retrieve the Implementation-Version string from the Jar file
     * that contains the specified Class.
     *
     * @param clazz a Class unique to the jar file we are looking for.
     * @return the version string from the Jar file or the empty string
     * ("") if none found.
     */
    public static String getJarVersion(Class<?> clazz) {
        String classPath = "/" + clazz.getName().replace('.', '/')
                + ".class";
        URL classUrl = clazz.getResource(classPath);
        if (classUrl == null) {
            LOGGER.warning("Error accessing Jar Manifest for " + clazz);
            return "";
        }

        // The classUrl may not be a jar: URL, depending on the servlet
        // container, so we can't just open it and assume we'll get a
        // JarURLConnection to get the manifest from. So we construct an
        // URL directly to the manifest we want.
        String classUrlRep = classUrl.toString();
        String path = classUrlRep.replace(classPath,
                "/META-INF/MANIFEST.MF");
        if (path.equals(classUrlRep)) {
            // The replace failed; we don't have an URL to read the manifest from.
            LOGGER.warning("Error accessing Jar Manifest for "
                    + classUrlRep);
            return "";
        }
        try {
            URL url = new URL(path);
            InputStream in = url.openStream();
            Manifest manifest = new Manifest(in);
            Attributes attrs = manifest.getMainAttributes();
            String version = attrs.getValue("Implementation-Version");
            return (version == null) ? "" : version;
        } catch (IOException e) {
            LOGGER.log(Level.WARNING, "Error accessing Jar Manifest for "
                    + path, e);
        }
        return ""; // Can't get version string.
    }
}

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