Gradle's bootRun and Window's command length limit

Thomas Uhrig · January 7, 2016

coding   java   spring

Sometimes Gradle’s bootRun and Window’s command length limit are two opponents. If you use bootRun to start your Spring Boot app from Gradle all class path dependencies will be added to the start command. Gradle will run something like this in the end:

java -jar MyApp.jar -classpath xx.jar,yy.jar,zz.jar,...

That’s fine and will work for a really long time. But as longer you work on your project you will add more and more dependencies. And it might happen that you cross a secret line of no return: 32767. That’s the number of characters which Windows’ CreateProcess function will accept. Any additional character will cause an exception:

CreateProcess error=206, The filename or extension is too long.

Sh*t! So how to start your app? With Gradle, you can use a simple workaround: Instead of appending all your dependencies to the start command, you create a JAR file with a manifest file. This manifest file contains all dependencies and will be the only dependency in your start command:

java -jar MyApp.jar -classpath pathing.jar

In Gradle code, this looks like this:

task pathingJar(type: Jar) {
    dependsOn configurations.runtime
    appendix = 'pathing'

    doFirst {
        manifest {
            attributes "Class-Path": configurations.runtime.files.collect {
                it.toURL().toString().replaceFirst(/file:/+/, '/')
            }.join(' ')
        }
    }
}

bootRun {
    dependsOn pathingJar
    doFirst {
        classpath = files("$buildDir/classes/main", "$buildDir/resources/main", pathingJar.archivePath)
    }
}

The pathingJar task creates a JAR file with a manifest file containing all our dependencies. This file will become pretty big, but that’s totally fine. Now we only extend the bootRun task to use this pathing JAR. This will solve the problem.

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Best regards, Thomas.