Is it possible to have persistence.xml in a location other than META-INF?

Question

I want to have my persistence.xml in conf folder of my app. How can I tell Persistence.createEntityManagerFactory that it should read it from there?

Answer 1

My solution is for EclipseLink 2.7.0 and Java 9 and it is modified and detailed version of @Evgeniy Dorofeev answer.

In org.eclipse.persistence.internal.jpa.deployment.PersistenceUnitProcessor on line 236 we see the following code:

URL puRootUrl = computePURootURL(descUrl, descriptorPath);

This code is used by EclipseLink to compute root url of the persistence.xml path. That's very important because final path will be made by adding descriptorPath to puRootUrl.

So, let's suppose we have file on /home/Smith/program/some-folder/persistence.xml, then we have:

Thread currentThread = Thread.currentThread();
ClassLoader previousClassLoader = currentThread.getContextClassLoader();
Thread.currentThread().setContextClassLoader(new ClassLoader(previousClassLoader) {
    @Override
    public Enumeration<URL> getResources(String name) throws IOException {
        if (name.equals("some-folder/persistence.xml")) {
            URL url = new File("/home/Smith/program/some-folder/persistence.xml").toURI().toURL();
            return Collections.enumeration(Arrays.asList(url));
        }
        return super.getResources(name);
    }

});
Map<String, String> properties = new HashMap<>();
properties.put("eclipselink.persistencexml", "some-folder/persistence.xml");
try {
    entityManagerFactory = Persistence.createEntityManagerFactory("unit-name", properties);
} catch (Exception ex) {
    logger.error("Error occured creating EMF", ex);
} finally {
    currentThread.setContextClassLoader(previousClassLoader);
}

Details:

1. Pay attention that when creating new class loader I pass there previous classloader otherwise it doesn't work.
2. We set property eclipselink.persistencexml. If we don't do that then default descriptorPath will be equal to META-INF/persistence.xml and we would need to keep our persistence.xml on /home/Smith/program/META-INF/persistence.xml to be found.

Answer 2

This solution worked for me

    Thread.currentThread().setContextClassLoader(new ClassLoader() {
        @Override
        public Enumeration<URL> getResources(String name) throws IOException {
            if (name.equals("META-INF/persistence.xml")) {
                return Collections.enumeration(Arrays.asList(new File("conf/persistence.xml")
                        .toURI().toURL()));
            }
            return super.getResources(name);
        }
    });
    Persistence.createEntityManagerFactory("test");