in src/main/java/org/apache/maven/plugins/war/packaging/OverlayPackagingTask.java [95:106]
protected File unpackOverlay(WarPackagingContext context, Overlay overlay) throws MojoExecutionException {
final File tmpDir = getOverlayTempDirectory(context, overlay);
// TODO: not sure it's good, we should reuse the markers of the dependency plugin
if (FileUtils.sizeOfDirectory(tmpDir) == 0
|| overlay.getArtifact().getFile().lastModified() > tmpDir.lastModified()) {
doUnpack(context, overlay.getArtifact().getFile(), tmpDir);
} else {
context.getLog().debug("Overlay [" + overlay + "] was already unpacked");
}
return tmpDir;
}