Improves console and GUI messages

Adds newlines when writing to console
Add Error: on lines containing an error
Makes it clearer when a jar build is successful
Makes failures show errors rather than throwing exceptions

src/main/java/net/knarcraft/minecraftserverlauncher/userinterface/MessageHandler.java

@@ -27,7 +27,9 @@ public abstract class MessageHandler implements GUI {
     public void showError(String title, String message) {
         if (silent) {
             try {
+                writer.write("Error: ");
                 writer.write(message);
+                writer.newLine();
                 writer.flush();
             } catch (IOException e) {
                 System.out.println(message);
@@ -47,6 +49,7 @@ public abstract class MessageHandler implements GUI {
         if (silent) {
             try {
                 writer.write(message);
+                writer.newLine();
                 writer.flush();
             } catch (IOException e) {
                 System.out.println(message);

src/main/java/net/knarcraft/minecraftserverlauncher/utility/JarBuilder.java

@@ -42,11 +42,10 @@ public class JarBuilder {
         downloadBuildTools();
         ProcessBuilder processBuilder = new ProcessBuilder("java", "-jar", "BuildTools.jar", "--rev",
                 "latest", "--output-dir", jarDirectory);
-        executeBuildProcess(processBuilder);
-        gui.setStatus("Finished building spigot .jar. Moving it to the correct location");
-        moveBuiltJar("spigot-", "SpigotLatest.jar");
+        if (executeBuildProcess(processBuilder) && moveBuiltJar("spigot-", "SpigotLatest.jar")) {
             gui.setStatus("Finished moving spigot.jar");
         }
+    }
 
     /**
      * Builds the latest version of the craftbukkit .jar file
@@ -55,11 +54,10 @@ public class JarBuilder {
         downloadBuildTools();
         ProcessBuilder processBuilder = new ProcessBuilder("java", "-jar", "BuildTools.jar", "--compile",
                 "craftbukkit", "--rev", "latest", "--output-dir", jarDirectory);
-        executeBuildProcess(processBuilder);
-        gui.setStatus("Finished building craftbukkit .jar. Moving it to the correct location");
-        moveBuiltJar("craftbukkit-", "BukkitLatest.jar");
+        if (executeBuildProcess(processBuilder) && moveBuiltJar("craftbukkit-", "BukkitLatest.jar")) {
             gui.setStatus("Finished moving craftbukkit.jar");
         }
+    }
 
     /**
      * Downloads the latest BuildTools version
@@ -88,27 +86,32 @@ public class JarBuilder {
      * Moves a built .jar file to its target file
      * @param searchString <p>The start of the name of the built file used to find it</p>
      * @param newName <p>The new name of the built file</p>
+     * @return <p>True if the .jar file was moved successfully</p>
      */
-    private void moveBuiltJar(String searchString, String newName) {
+    private boolean moveBuiltJar(String searchString, String newName) {
         File[] foundFiles = new File(jarDirectory).listFiles((file) -> file.isFile() && file.getName().startsWith(searchString));
         if (foundFiles != null && foundFiles.length == 1) {
             File newFileLocation = new File(jarDirectory + File.separator + newName);
             if (newFileLocation.exists()) {
                 if (!newFileLocation.delete()) {
-                    throw new IllegalArgumentException("Unable to delete previously built .jar");
+                    gui.showError("Unable to delete previously built .jar");
                 }
             }
             if (!foundFiles[0].renameTo(newFileLocation)) {
-                throw new IllegalArgumentException("Unable to move built .jar");
+                gui.showError("Unable to move built .jar");
+            } else {
+                return true;
             }
         }
+        return false;
     }
 
     /**
      * Starts the build process and initializes
      * @param processBuilder <p>The process builder to execute</p>
+     * @return <p>True if the process exited successfully</p>
      */
-    private void executeBuildProcess(ProcessBuilder processBuilder) {
+    private boolean executeBuildProcess(ProcessBuilder processBuilder) {
         processBuilder.directory(new File(buildDirectory));
         processBuilder.redirectErrorStream(true);
         try {
@@ -120,16 +123,20 @@ public class JarBuilder {
                 writer.write(CommonFunctions.readBufferedReader(reader));
             } while (process.isAlive());
 
+            writer.newLine();
             writer.flush();
 
             if (process.exitValue() == 0) {
-                gui.setStatus("Jar building process finished successfully.");
+                gui.showMessage("Jar building process finished successfully.");
+                return true;
             } else {
-                throw new RuntimeException("Jar building process failed with exit code " + process.exitValue() + ".");
+                gui.showError("Jar building process failed with exit code " + process.exitValue() +
+                        ". Please check the BuildTools log for errors.");
             }
         } catch (IOException e) {
             e.printStackTrace();
         }
+        return false;
     }
 
     /**

src/test/java/net/knarcraft/minecraftserverlauncher/userinterface/FakeGUI.java

@@ -21,6 +21,7 @@ public class FakeGUI extends MessageHandler implements GUI {
     public void setStatus(String message) {
         try {
             writer.write(message);
+            writer.newLine();
             writer.flush();
         } catch (IOException e) {
             System.out.println(message);