Open on running feature

build.gradle

@@ -23,7 +23,7 @@ java {
 }
 
 group = 'online.hatsunemiku'
-version = '1.13.0'
+version = '1.13.1'
 sourceCompatibility = JavaVersion.VERSION_21
 targetCompatibility = JavaVersion.VERSION_21
 

src/main/java/online/hatsunemiku/tachideskvaadinui/TachideskVaadinUiApplication.java

@@ -6,7 +6,10 @@
 
 package online.hatsunemiku.tachideskvaadinui;
 
+import java.io.IOException;
+import java.net.ServerSocket;
 import lombok.extern.slf4j.Slf4j;
+import online.hatsunemiku.tachideskvaadinui.utils.BrowserUtils;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.builder.SpringApplicationBuilder;
@@ -34,11 +37,51 @@ public class TachideskVaadinUiApplication {
   public static void main(String[] args) {
     boolean headless = Boolean.parseBoolean(System.getProperty("vaaui.headless"));
 
+    if (isRunningAlready()) {
+      log.warn("Application is already running.");
+      runAlreadyRunningTasks(headless);
+      System.exit(0);
+    }
+
     log.info("Is headless: {}", headless);
 
     SpringApplication app =
         new SpringApplicationBuilder(TachideskVaadinUiApplication.class).headless(headless).build();
 
     app.run(args);
   }
+
+  /**
+   * Runs the tasks that should be run when the application is already running.
+   *
+   * @param headless Whether the application is running in headless mode
+   */
+  private static void runAlreadyRunningTasks(boolean headless) {
+    if (!headless) {
+      log.info("Opening browser...");
+
+      try {
+        BrowserUtils.openBrowser("http://localhost:3901");
+      } catch (IOException e) {
+        log.error("Failed to open browser.", e);
+      }
+    }
+  }
+
+  /**
+   * Checks if the application is already running.
+   *
+   * @return {@code true} if the application is already running, {@code false} otherwise
+   */
+  private static boolean isRunningAlready() {
+    int port = 3901;
+    try (ServerSocket ignored =
+        new ServerSocket(
+            port)) { // skipcq: JAVA-S1011 - Not a security risk, because the socket is closed
+      // immediately.
+      return false;
+    } catch (IOException e) {
+      return true;
+    }
+  }
 }