Java live-reload with HotSwap agent is semi-working

[mshabarov]

Description of the bug

HotSwap agent live-reload works unstable - works only for first reload on some machines, somewhere it works without issues.

For testing results on Mac, see my comments here and here.

Windows:
Hotswap state is shown correctly on the info Window. 24.3.10 and snapshot initial compile and reload passes fine, but does not refresh the client. There is a new Java live reload available: HotswapAgent info on the debug window.
After the initial reload further reloads get an exception:

HOTSWAP AGENT: 09:39:12.302 WARNING (org.hotswap.agent.plugin.vaadin.VaadinIntegration) - Unable to obtain ApplicationRouteRegistry instance; routes are not updated:
java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.hotswap.agent.plugin.vaadin.VaadinIntegration.updateRoutes(VaadinIntegration.java:81)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.hotswap.agent.command.ReflectionCommand.doExecuteReflectionCommand(ReflectionCommand.java:207)
    at org.hotswap.agent.command.ReflectionCommand.executeCommand(ReflectionCommand.java:168)
    at org.hotswap.agent.plugin.vaadin.VaadinPlugin$UpdateRoutesCommand.executeCommand(VaadinPlugin.java:165)
    at org.hotswap.agent.command.impl.CommandExecutor.run(CommandExecutor.java:43)
Caused by: java.lang.ClassCastException: Cannot cast com.vaadin.flow.server.startup.ApplicationRouteRegistry$ApplicationRouteRegistryWrapper to com.vaadin.flow.server.startup.ApplicationRouteRegistry$ApplicationRouteRegistryWrapper
    at java.base/java.lang.Class.cast(Class.java:3889)
    at com.vaadin.flow.server.VaadinServletContext.getAttribute(VaadinServletContext.java:76)
    at com.vaadin.flow.server.VaadinContext.getAttribute(VaadinContext.java:58)
    at com.vaadin.flow.server.startup.ApplicationRouteRegistry.getInstance(ApplicationRouteRegistry.java:112)
    ... 13 more

The server mostly survives and reloads correctly after, but the client doesn't reload.
At times the server dies on the second reload with:

jakarta.servlet.ServletException: java.lang.reflect.InvocationTargetException
    at com.vaadin.flow.server.startup.ClassLoaderAwareServletContainerInitializer.lambda$onStartup$2 (ClassLoaderAwareServletContainerInitializer.java:103)
    at com.vaadin.flow.server.startup.ClassLoaderAwareServletContainerInitializer.onStartup (ClassLoaderAwareServletContainerInitializer.java:122)
    at org.eclipse.jetty.servlet.ServletContainerInitializerHolder.doStart (ServletContainerInitializerHolder.java:148)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.start (AbstractLifeCycle.java:93)
    at org.eclipse.jetty.util.component.ContainerLifeCycle.start (ContainerLifeCycle.java:171)
    at org.eclipse.jetty.util.component.ContainerLifeCycle.doStart (ContainerLifeCycle.java:114)
    ...
Caused by: java.lang.ClassCastException: Cannot cast com.vaadin.flow.server.startup.DeferredServletContextInitializers to com.vaadin.flow.server.startup.DeferredServletContextInitializers
    at java.lang.Class.cast (Class.java:3889)
    at com.vaadin.flow.server.VaadinServletContext.getAttribute (VaadinServletContext.java:76)
    at com.vaadin.flow.server.VaadinContext.getAttribute (VaadinContext.java:58)
    at com.vaadin.flow.server.startup.LookupServletContainerInitializer.lambda$process$0 (LookupServletContainerInitializer.java:110)
    at com.vaadin.flow.di.LookupInitializer.initialize (LookupInitializer.java:283)

and it doesn't seem to get back up even with consecutive class reloads/rebuilds.

Expected behavior

Live-reload works without exceptions.

Minimal reproducible example

Test with the steps described in this ticket, the same instructions basically as described in the Vaadin online docs.

Versions

• Vaadin / Flow version: latest versions of 24.3 and 24.4
• Java version: JBR 17.0.10
• OS version: Mac, Windows
• Browser version (if applicable): Chrome
• Application Server (if applicable): Jetty
• IDE (if applicable): IDEA

[jorgheymans]

I have observed this as well lately, the browser "sometimes" no longer refreshes after a recompile of a class is triggered in Intellij. (this is on Ubuntu LTS, latest Vaadin 24.3)

[echarlus]

Hi, I'm also experiencing this issue on mac (aarch64) with latest Hotswap version and Vaadin 23.4.x (currently 24.3.10)
See my post here
Hotswap seems to works randomly ...