Devtools doesn't work with classpath file mode in Idea

[mraszplewicz]

We have very long classpath in our application so Idea can't run it without switching to "classpath file mode" (dynamic.classpath=true in .idea/workspace.xml). When I enable this mode devtools doesn't work.

Idea generates temporary jar file with Class-Path in MANIFEST.MF (C:\Users\USER_NAME\AppData\Local\Temp\classpathX.jar).

I was trying to debug the problem. This generated jar is treated as non reloadable in org.springframework.boot.devtools.restart.ChangeableUrls class.

[philwebb]

I'm not that familiar with this technique. Does classpathX.jar only contain a MANIFEST.MF file? Are there any other URLs passed to the ChangeableUrls constructor?

[snicoll]

ping @YannCebron

[akozlova]

classpathX.jar contains a manifest with Class-Path attribute which contains all the urls of the initial classpath. That's the official way to collapse too long classpaths from Oracle: e.g. https://docs.oracle.com/javase/tutorial/deployment/jar/downman.html. It's possible to force IDEA to switch back to the CommandLineWrapper with urls written to the file but this could add another problems with classloaders so I would advise not to do that if anyhow possible.
Anna

[mraszplewicz]

I've created sample project: https://github.com/mraszplewicz/springboot-dynamic-classpath
You have to open it in IntelliJ Idea, refresh gradle projects and run.

I have breakpoint in line 42 of class ChangeableUrls. There are only two urls passed to constructor: classpath47.jar and gragent.jar (something added by Idea).

Please find classpath47.jar attached.
classpath47.zip

[akozlova]

@mraszplewicz
And the manifest contains the whole classpath in the Class-Path attribute. My comment was adressed to @philwebb, sorry if I confused you

[mraszplewicz]

@akozlova Yes it does contain whole classpath. I'm not confused:) I am responding to @philwebb first comment. I'm not as fast as You are:)

[philwebb]

Thanks for the feedback. It looks like the current way we obtain the classpath (via URLClassLoader) isn't enough when using the META-INF/MANIFEST.MF technique.

[wilkinsona]

@mraszplewicz Thanks for the sample. Unfortunately, it doesn't reproduce the problem for me. I'm using IDEA 15. With dynamic.classpath set to true DevTools doesn't get loaded at all, let alone fail to detect that the context should have restarted. As far as I can tell IDEA is omitting it from the classpath. If I set dynamic.classpath to false then everything works as expected: DevTools loads when the application launches and restarts the context when I make a change and build the project. What have I missed?