Allow universalJavaAppStub and Why launcher to be overridden by user …

src/main/java/io/github/fvarrui/javapackager/packagers/CreateWindowsExeWhy.java

@@ -53,7 +53,7 @@ protected File doApply(WindowsPackager packager) throws Exception {
 		FileUtils.copyFileToFile(iconFile, getGenericIcon());
 
 		// creates generic exe
-		FileUtils.copyResourceToFile("/windows/JavaLauncher.exe", getGenericExe());
+		FileUtils.copyResourceToFile("/windows/JavaLauncher.exe", getGenericExe(), packager);
 
 		// copies rcedit command line tool (needed to manipulate exe)
 		File rcedit = new File(getOutputFolder(), "rcedit.exe");

src/main/java/io/github/fvarrui/javapackager/packagers/MacPackager.java

@@ -113,7 +113,7 @@ public File doCreateApp() throws Exception {
 
 		// copies universalJavaApplicationStub startup file to boot java app
 		File appStubFile = new File(macOSFolder, "universalJavaApplicationStub");
-		FileUtils.copyResourceToFile("/mac/universalJavaApplicationStub", appStubFile, true);
+		FileUtils.copyResourceToFile("/mac/universalJavaApplicationStub", appStubFile, true, this);
 		FileUtils.processFileContent(appStubFile, content -> {
 			if (!macConfig.isRelocateJar()) {
 				content = content.replaceAll("/Contents/Resources/Java", "/Contents/Resources");

src/main/java/io/github/fvarrui/javapackager/utils/FileUtils.java

@@ -17,13 +17,15 @@
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.util.Arrays;
 import java.util.List;
 import java.util.function.Function;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
+import io.github.fvarrui.javapackager.packagers.Packager;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang3.StringUtils;
 
@@ -191,9 +193,13 @@ private static void copyStreamToFile(InputStream is, File dest) throws Exception
             throw new Exception("Could not copy input stream to " + dest, ex);
         }
 	}
-
-	public static void copyResourceToFile(String resource, File dest, boolean unixStyleNewLines) throws Exception  {
-		copyResourceToFile(resource, dest);
+
+	public static void copyResourceToFile(String resource, File dest, boolean unixStyleNewLines) throws Exception {
+		copyResourceToFile(resource, dest, unixStyleNewLines, null);
+	}
+
+	public static void copyResourceToFile(String resource, File dest, boolean unixStyleNewLines, Packager packager) throws Exception  {
+		copyResourceToFile(resource, dest, packager);
 		if (unixStyleNewLines) {
 			try {
 				processFileContent(dest, c -> c.replaceAll("\\r\\n", "\n").replaceAll("\\r", "\n"));
@@ -208,8 +214,22 @@ public static void processFileContent(File dest, Function<String, String> functi
 		content = function.apply(content);
 		writeStringToFile(dest, content, StandardCharsets.UTF_8);
 	}
-
-	public static void copyResourceToFile(String resource, File dest) throws Exception  {
+
+	public static void copyResourceToFile(String resource, File dest) throws Exception {
+		copyResourceToFile(resource, dest, null);
+	}
+
+	public static void copyResourceToFile(String resource, File dest, Packager packager) throws Exception  {
+		if (packager != null) {
+			String rsc = resource.startsWith("/") ? resource.substring(1) : resource;
+			Path asset = packager.getAssetsDir().toPath().resolve(rsc);
+			if (Files.exists(asset)) {
+				Logger.info("Copying resource [" + asset + "] to file [" + dest + "]");
+				copyFileToFile(asset.toFile(), dest);
+				return;
+			}
+		}
+
 		Logger.info("Copying resource [" + resource + "] to file [" + dest + "]");		
 		copyStreamToFile(FileUtils.class.getResourceAsStream(resource), dest);
 	}