How do you create a MANIFEST.MF that's available when you're testing and running from a jar in production?

Question

I've spent far too much time trying to figure this out. This should be the simplest thing and everyone who distributes Java applications in jars must have to deal with it.

I just want to know the proper way to add versioning to my Java app so that I can access the version information when I'm testing, e.g. debugging in Eclipse and running from a jar.

Here's what I have in my build.xml:

<target name="jar" depends = "compile">
    <property name="version.num" value="1.0.0"/>
    <buildnumber file="build.num"/>
    <tstamp>
        <format property="TODAY" pattern="yyyy-MM-dd HH:mm:ss" />
    </tstamp>

    <manifest file="${build}/META-INF/MANIFEST.MF">
        <attribute name="Built-By" value="${user.name}" />
        <attribute name="Built-Date" value="${TODAY}" />                   
        <attribute name="Implementation-Title" value="MyApp" />
        <attribute name="Implementation-Vendor" value="MyCompany" />                
        <attribute name="Implementation-Version" value="${version.num}-b${build.number}"/>                              
    </manifest>

    <jar destfile="${build}/myapp.jar" basedir="${build}" excludes="*.jar" />                   
</target>

This creates /META-INF/MANIFEST.MF and I can read the values when I'm debugging in Eclipse thusly:

public MyClass()
{
    try
    {                        
        InputStream stream = getClass().getResourceAsStream("/META-INF/MANIFEST.MF");
        Manifest manifest = new Manifest(stream);            

        Attributes attributes = manifest.getMainAttributes();

        String implementationTitle = attributes.getValue("Implementation-Title");
        String implementationVersion = attributes.getValue("Implementation-Version");
        String builtDate = attributes.getValue("Built-Date");
        String builtBy = attributes.getValue("Built-By");
   }
   catch (IOException e)
   {            
        logger.error("Couldn't read manifest.");
   }        

}

But, when I create the jar file, it loads the manifest of another jar (presumably the first jar loaded by the application - in my case, activation.jar).

Also, the following code doesn't work either although all the proper values are in the manifest file.

    Package thisPackage = getClass().getPackage();
    String implementationVersion = thisPackage.getImplementationVersion();

Any ideas?

Answer 1

You can get the manifest for an arbitrary class in an arbitrary jar without parsing the class url (which could be brittle). Just locate a resource that you know is in the jar you want, and then cast the connection to JarURLConnection.

If you want the code to work when the class is not bundled in a jar, add an instanceof check on the type of URL connection returned. Classes in an unpacked class hierarchy will return a internal Sun FileURLConnection instead of the JarUrlConnection. Then you can load the Manifest using one of the InputStream methods described in other answers.

@Test
public void testManifest() throws IOException {
    URL res = org.junit.Assert.class.getResource(org.junit.Assert.class.getSimpleName() + ".class");
    JarURLConnection conn = (JarURLConnection) res.openConnection();
    Manifest mf = conn.getManifest();
    Attributes atts = mf.getMainAttributes();
    for (Object v : atts.values()) {
        System.out.println(v);
    }
}

Answer 2

ClassLoader.getResource(String) will load the first manifest it finds on the classpath, which may be the manifest for some other JAR file. Thus, you can either enumerate all the manifests to find the one you want or use some other mechanism, such as a properties file with a unique name.