Gradle 4: Copy War to Directory

This took me 90 minutes to figure out and the internet was no help.

I was trying to copy the output of my gradle war project to a Tomcat webapps directory so I can run it in the debugger. 

I defined "tomcathome" in gradle.properties.  So far so good.

Then after reading a bunch of confusing stuff about how to define gradle tasks, I came up with this:

    task deployTomcat (dependsOn: 'war') {
        doLast {
            mkdir "${tomcathome}/webapps/${project.name}"
            copy {
                from zipTree(war)
                into "${tomcathome}/webapps/${project.name}"
            }
        }
    }

This task got an error:

Execution failed for task ':deployTomcat'.
> Cannot convert the provided notation to a File or URI: task ':war'.
  The following types/formats are supported:
    - A String or CharSequence path, for example 'src/main/java' or '/usr/include'.
    - A String or CharSequence URI, for example 'file:/usr/include'.
    - A File instance.
    - A Path instance.
    - A URI or URL instance.

So it doesn't like 'zipTree(war)'.  I modified the code to print 'war' and 'war.outputs'.  'war.outputs' is an instance of org.gradle.api.internal.tasks.DefaultTaskOutputs. 

So I googled this, found the source on github, found that DefaultTaskOutputs has a 'files' property of type FileCollection, and FileCollection has a property called 'singleFile'.  So I added more prints and found that war.outputs.files.singleFile gives me the name of the war file.

So this is the working task:

task deployTomcat (dependsOn: 'war') {
    doLast {
        mkdir "${tomcathome}/webapps/${project.name}"
        copy {
            from zipTree(war.outputs.files.singleFile)
            into "${tomcathome}/webapps/${project.name}"
        }
    }
}

Yay.