WIP: Refactor how sysprop fallback values are done

src/main/java/net/imagej/ui/swing/updater/LauncherMigrator.java

@@ -316,29 +316,28 @@ private void switchToNewLauncher() {
 		// In order to trigger it successfully, we need to set various properties:
 
 		File appConfigFile = new File(configDir, appSlug + ".toml");
-		File appUserConfigFile = new File(configDir, appSlug + ".cfg");
 		List<String> lines;
 		try {
 			lines = Files.readAllLines(appConfigFile.toPath());
 		}
 		catch (IOException exc) {
 			log.debug(exc);
-			// Couldn't read from the config file; define some fallback values.
-			lines = Arrays.asList(
-				"-Dscijava.app.java-links='https://downloads.imagej.net/java/jdk-urls.txt',",
-				"-Dscijava.app.java-version-minimum=8,",
-				"-Dscijava.app.java-version-recommended=21,",
-				"-Dscijava.app.config-file='" + appUserConfigFile.getPath() + "',"
-			);
+			// Couldn't read from the config file.
+			lines = new ArrayList<>();
 		}
+
 		setPropertyIfNull("scijava.app.name", appTitle);
+
 		Path splashImage = appDir.toPath().resolve("images").resolve("icon.png");
 		setPropertyIfNull("scijava.app.splash-image", splashImage.toString());
-		extractAndSetProperty("scijava.app.java-links", lines);
-		extractAndSetProperty("scijava.app.java-version-minimum", lines);
-		extractAndSetProperty("scijava.app.java-version-recommended", lines);
-		extractAndSetProperty("scijava.app.config-file", lines);
-		setPropertyIfNull("scijava.app.config-file", appUserConfigFile.getPath());
+
+		extractAndSetProperty("scijava.app.java-links", lines,
+			"https://downloads.imagej.net/java/jdk-urls.txt");
+		extractAndSetProperty("scijava.app.java-version-minimum", lines, "8");
+		extractAndSetProperty("scijava.app.java-version-recommended", lines, "21");
+		extractAndSetProperty("scijava.app.config-file", lines,
+			new File(configDir, appSlug + ".cfg").getPath());
+
 		String platform = UpdaterUtil.getPlatform();
 		// FIXME: I think the macOS platform will be wrong here. It needs -arm64 suffix!
 		setPropertyIfNull("scijava.app.java-platform", platform);
@@ -508,13 +507,17 @@ private static void setPropertyIfNull(String name, String value) {
 		if (System.getProperty(name) == null) System.setProperty(name, value);
 	}
 
-	private static void extractAndSetProperty(String name, List<String> lines) {
+	private static void extractAndSetProperty(
+		String name,
+		List<String> lines,
+		String fallbackValue)
+	{
 		// No, the following replacement does not escape all problematic regex
 		// characters. But the properties we're working with here are only
 		// alphameric with dot separators, so it's OK. Hooray for pragmatism!
 		String escaped = name.replaceAll("\\.", "\\\\.");
 		Pattern p = Pattern.compile(".*'-D" + escaped + "=['\"]?(.*?)['\"]?,$");
-		String value = null;
+		String value = fallbackValue;
 		for (String line : lines) {
 			Matcher m = p.matcher(line);
 			if (m.matches()) {