refactor: extract AppVersion for /version resource

src/main/java/core/packetproxy/PacketProxy.java

@@ -16,10 +16,9 @@
 package packetproxy;
 
 import java.io.File;
-import java.io.InputStream;
 import java.sql.SQLException;
 import javax.swing.*;
-import org.apache.commons.io.IOUtils;
+import packetproxy.common.AppVersion;
 import packetproxy.common.I18nString;
 import packetproxy.common.Utils;
 import packetproxy.gui.GUIMain;
@@ -119,11 +118,7 @@ public void start() throws Exception {
 	}
 
 	private void startGUI() throws Exception {
-		String version = "1.0.0";
-		InputStream versionStream = getClass().getResourceAsStream("/version");
-		if (versionStream != null) {
-			version = IOUtils.toString(versionStream);
-		}
+		var version = AppVersion.get();
 		gui = GUIMain.getInstance(String.format("PacketProxy %s", version));
 		gui.setVisible(true);
 	}

src/main/java/core/packetproxy/common/AppVersion.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2026 DeNA Co., Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package packetproxy.common;
+
+import java.io.IOException;
+import java.io.InputStream;
+import org.apache.commons.io.IOUtils;
+
+public final class AppVersion {
+
+	private static final String DEFAULT_VERSION = "1.0.0";
+	private static String cached;
+
+	private AppVersion() {
+	}
+
+	public static String get() {
+		if (cached == null) {
+
+			cached = load();
+		}
+		return cached;
+	}
+
+	private static String load() {
+		try (InputStream in = AppVersion.class.getResourceAsStream("/version")) {
+			if (in == null) {
+
+				return DEFAULT_VERSION;
+			}
+			return IOUtils.toString(in).trim();
+		} catch (IOException e) {
+
+			return DEFAULT_VERSION;
+		}
+	}
+}