What causes "Unable to access [{}]" in hibernate/hibernate-orm?

Check the resource name in the message and open it manually (new URL(...).openConnection()) to reproduce the failure outside Hibernate.

hibernate/hibernate-orm · error · PersistenceException

Unable to access [{}]

Error message

Unable to access [{}]

What it means

Thrown by PersistenceXmlParser.loadUrlWithJaxb() as a PersistenceException when xmlUrl.openConnection() itself raises an IOException before any stream is obtained - i.e. the URL to a persistence.xml cannot be connected to at all. It is the outer catch, distinguishing 'cannot connect to the resource' (this error) from 'connected but could not read' (the input-stream error).

Source

Thrown at hibernate-core/src/main/java/org/hibernate/jpa/boot/spi/PersistenceXmlParser.java:330

	private JaxbPersistenceImpl loadUrlWithJaxb(URL xmlUrl) {
		final String resourceName = xmlUrl.toExternalForm();
		try {
			var connection = xmlUrl.openConnection();
			// avoid JAR locking on Windows and Tomcat
			connection.setUseCaches( false );
			try ( var inputStream = connection.getInputStream() ) {
				return new ConfigurationBinder( classLoaderService )
						.bind( new StreamSource( inputStream ),
								new Origin( SourceType.URL, resourceName ) )
						.getRoot();
			}
			catch (IOException e) {
				throw new PersistenceException( "Unable to obtain input stream from [" + resourceName + "]", e );
			}
		}
		catch (IOException e) {
			throw new PersistenceException( "Unable to access [" + resourceName + "]", e );
		}
	}

}

View on GitHub (pinned to fad1729dce)

Solutions

Check the resource name in the message and open it manually (new URL(...).openConnection()) to reproduce the failure outside Hibernate.
Use a classloader/protocol setup that supports the URL scheme (e.g. Spring Boot's LaunchedURLClassLoader, proper VFS integration) so Hibernate receives only handler-supported URLs.
Run from an exploded/classic jar layout if nested-jar URL handling keeps failing.
Ensure the artifact and all classpath entries are stable (not deleted/moved) for the whole duration of bootstrap.

Example fix

# before: java -cp 'app.jar:lib/*' ...  with lib jar referenced via nested jar: URL
# after: run as an executable jar so Spring Boot's LaunchedURLClassLoader resolves nested entries
java -jar app.jar

Defensive patterns

Strategy: try-catch

Validate before calling

// reproduce the connect outside Hibernate to verify URL support
for (URL u : Collections.list(cl.getResources("META-INF/persistence.xml"))) {
    try { u.openConnection(); } catch (IOException io) { throw new IllegalStateException("Unsupported/unreachable URL: " + u, io); }
}

Try / catch

catch (PersistenceException e) {
    if (e.getMessage() != null && e.getMessage().contains("Unable to access")) {
        log.error("Cannot connect to persistence.xml URL: {} - check nested-jar/VFS URL support", e.getMessage());
    }
    throw e;
}

Prevention

Use the launcher's intended classloader (e.g. Spring Boot's LaunchedURLClassLoader) so nested-jar URLs resolve.
Prefer exploded or classic single-jar layouts when custom URL schemes are involved.

When it happens

Trigger: A persistence.xml URL whose protocol handler fails on connect: nested-jar URLs (jar:...jar!/META-INF/persistence.xml) unsupported by the JDK handler, virtual-filesystem URLs from app servers, file URLs to paths that no longer exist, or http URLs whose host refuses the connection.

Common situations: Spring Boot executable (nested) jars with a ClassLoader that leaks the inner jar URL to Hibernate; running on containers/modules systems (JBoss VFS) whose custom URL schemes confuse plain URLConnection; the archive being deleted or moved after classpath scanning catalogued it.

Related errors

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/845513ea10d9d643. Report an issue: GitHub.