How to execute code only ONCE - even in dev mode?

[col-panic]

I have the following code

 */
@ApplicationScoped
public class ApplicationService {

    @Startup
    void init() {
        // FIXME multiple calls lead to hanging dev mode
        URL.setURLStreamHandlerFactory(new SmbUrlStreamHandlerFactory());
    }

to support smb:// urls in my application. Now in dev mode, after the first reload, Quarkus keeps crashing with

2025-06-17 09:51:37,919 ERROR [io.qua.run.Application] (Quarkus Main Thread) Failed to start application: java.lang.RuntimeException: Failed to start quarkus
        at io.quarkus.runner.ApplicationImpl.doStart(Unknown Source)
        at io.quarkus.runtime.Application.start(Application.java:101)
        at io.quarkus.runtime.ApplicationLifecycleManager.run(ApplicationLifecycleManager.java:119)
        at io.quarkus.runtime.Quarkus.run(Quarkus.java:80)
        at io.quarkus.runtime.Quarkus.run(Quarkus.java:51)
        at io.quarkus.runtime.Quarkus.run(Quarkus.java:144)
        at io.quarkus.runner.GeneratedMain.main(Unknown Source)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at io.quarkus.runner.bootstrap.StartupActionImpl$1.run(StartupActionImpl.java:121)
        at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: java.lang.Error: factory already defined
        at java.base/java.net.URL.setURLStreamHandlerFactory(URL.java:1392)
        at ch.myelexis.core.services.ApplicationService.init(ApplicationService.java:24)

What would be a proper way to solve this? Is there some Quarkus supported point to register url handlers? Is there some means to execute this code only once - even in dev mode? Anything else? Thanks!

[cwansart]

You could set a property boolean initialized and check that. Maybe not ideal, but very simple.

I'd guess that this is only relevant for dev mode though, but I don't see any big downside here, because in production it will run only once anyway.

[col-panic]

@cwansart do you mean a config property? And then using https://quarkus.io/guides/config#programmatically-access-the-configuration to set it?

[dmlloyd]

The challenge would be that if your code is reloaded with another class loader (likely), the variable would be false again.

[cwansart]

Oh, okay, then this would not work. Sorry

[dmlloyd]

A better solution could be to forget about using CDI for this and instead extend java.net.spi.URLStreamHandlerProvider with a corresponding META-INF/services file; this way the JDK will ensure that it is only loaded once.

[col-panic]

Thanks @dmlloyd for this approach! I tried this, but the behaviour seems very wierd. The functionality works via UnitTest in test mode, but fails in dev mode and ci test in dev mode AND in production?!

I created the file src/main/resources/META-INF/services/java.net.spi.URLStreamHandlerProvider with the single line ch.elexis.core.jcifs.SmbUrlStreamHandlerProvider both files are part of the created binary jar file.

[col-panic]

Could this problem relate to https://quarkus.io/guides/class-loading-reference#parent-first-dependencies ?