java：获得正确的资源

Question

I have a library foo.jar that contains an svnversion.properties file (just looks like svnversion=12345M or whatever) and the following static method in a class SVNVersion :

public static SVNVersion fromString(String s) { ... }
public static SVNVersion fromResources(Class<?> cl) {
    ResourceBundle svnversionResource = ResourceBundle.getBundle(
        "svnversion", Locale.getDefault(), cl.getClassLoader());
    if (svnversionResource.containsKey("svnversion"))
    {
        String svnv = svnversionResource.getString("svnversion");
        return fromString(svnv);
    }
    else
    {
        return null;
    }
}

I also have a library bar.jar that contains an svnversion.properties file as well (let's say it contains svnversion=789 ).

However, when I run the following within a class SomeClassInBarJar that's in bar.jar :

SVNVersion vfoo = SVNVersion.fromResources(SVNVersion.class);
SVNVersion vbar = SVNVersion.fromResources(SomeClassInBarJar.class);

and I print the result, I see 789 twice. Clearly I am not doing this right. How do I get the right svnversion.properties file in the root of the jar file containing a given class? (assuming it's there)

---

edit: I just tried

InputStream is = cl.getResourceAsStream("/svnversion.properties");

and it has the same problem. I seem to be able only to get access to the main jar file's /svnversion.properties and not the library's /svnversion.properties .

Answer 1

You obviously cannot use this approach, as whatever svnversion.properties file comes will always be used the classloader. It is the same behaviour you would see for classes: if two classes with the same name are on the classpath, it's whatever comes first that is used.

A (convoluted) approach would be to find out what jar a class belongs to, and then retrieve svnversion.properties in that jar:

public static JarFile getJarFile(Class<?> cl) {
    URL classUrl = cl.getResource(cl.getSimpleName() + ".class");
    if (classUrl != null) {
        try {
            URLConnection conn = classUrl.openConnection();
            if (conn instanceof JarURLConnection) {
                JarURLConnection connection = (JarURLConnection) conn;
                return connection.getJarFile();
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    return null;
}

public static SVNVersion fromResources(Class<?> cl) {
    JarFile jarFile = getJarFile(cl);
    ZipEntry entry = jarFile.getEntry("svnversion.properties");
    Properties props = new Properties();
    try {
        props.load(jarFile.getInputStream(entry));
    } catch (IOException e) {
        throw new RuntimeException(e);
    }

    if (props.containsKey("svnversion")) {
        String svnv = props.getProperty("svnversion");
        return fromString(svnv);
    } else {
        return null;
    }
}

That's why, IMHO, you'd probably be better off storing the svn version number in the class themselves as final static variables (and using svn $Revision$ keyword).