feat: detect installed Java runtime

README.md

@@ -7,6 +7,7 @@
 - интерактивный интерфейс профилей и настроек;
 - Tauri 2 native shell с безопасной командой `native_host`;
 - сохранение памяти профиля в локальном каталоге данных приложения;
+- безопасное обнаружение установленной Java (включая `JAVA_HOME`) перед запуском;
 - адаптивное окно для Windows, Linux и macOS;
 - базовая структура, в которую будут добавлены манифесты, проверка файлов,
   Java 21 и запуск Minecraft.

src-tauri/src/java.rs

@@ -0,0 +1,89 @@
+use serde::Serialize;
+use std::{env, path::PathBuf, process::Command};
+
+#[derive(Clone, Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct JavaInstallation {
+    pub executable: String,
+    pub major: u8,
+    pub version: String,
+}
+
+/// Finds a usable Java runtime without modifying the machine.
+///
+/// The launcher will later use this result to decide whether Java 21 needs to
+/// be bundled. We deliberately check JAVA_HOME first: it is explicit and makes
+/// development installations predictable across all supported platforms.
+pub fn detect() -> Option<JavaInstallation> {
+    candidates().into_iter().find_map(check_candidate)
+}
+
+fn candidates() -> Vec<PathBuf> {
+    let executable = if cfg!(target_os = "windows") {
+        "java.exe"
+    } else {
+        "java"
+    };
+
+    let mut candidates = Vec::new();
+    if let Some(java_home) = env::var_os("JAVA_HOME") {
+        candidates.push(PathBuf::from(java_home).join("bin").join(executable));
+    }
+    candidates.push(PathBuf::from(executable));
+    candidates
+}
+
+fn check_candidate(candidate: PathBuf) -> Option<JavaInstallation> {
+    let output = Command::new(&candidate).arg("-version").output().ok()?;
+    if !output.status.success() {
+        return None;
+    }
+
+    let source = format!(
+        "{}\n{}",
+        String::from_utf8_lossy(&output.stdout),
+        String::from_utf8_lossy(&output.stderr)
+    );
+    let version = parse_version(&source)?;
+    let major = parse_major(&version)?;
+    Some(JavaInstallation {
+        executable: candidate.display().to_string(),
+        major,
+        version,
+    })
+}
+
+fn parse_version(source: &str) -> Option<String> {
+    let marker = "version \"";
+    let start = source.find(marker)? + marker.len();
+    let remainder = &source[start..];
+    let end = remainder.find('"')?;
+    Some(remainder[..end].to_owned())
+}
+
+fn parse_major(version: &str) -> Option<u8> {
+    let mut segments = version.split('.');
+    let first = segments.next()?.parse::<u8>().ok()?;
+    if first == 1 {
+        segments.next()?.parse::<u8>().ok()
+    } else {
+        Some(first)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{parse_major, parse_version};
+
+    #[test]
+    fn parses_modern_java_version() {
+        let output = "openjdk version \"21.0.8\" 2025-07-15";
+        assert_eq!(parse_version(output).as_deref(), Some("21.0.8"));
+        assert_eq!(parse_major("21.0.8"), Some(21));
+    }
+
+    #[test]
+    fn parses_legacy_java_version() {
+        assert_eq!(parse_major("1.8.0_452"), Some(8));
+    }
+}

src-tauri/src/lib.rs

@@ -1,3 +1,4 @@
+mod java;
 mod manifest;
 mod profile;
 mod settings;
@@ -29,6 +30,12 @@ fn native_host(app: AppHandle) -> Result<NativeHost, String> {
     })
 }
 
+/// Detects an existing Java installation. This is read-only and never downloads Java.
+#[tauri::command]
+fn detect_java() -> Option<java::JavaInstallation> {
+    java::detect()
+}
+
 /// Validates an untrusted profile manifest before any file is downloaded.
 #[tauri::command]
 fn validate_manifest(manifest_json: String) -> Result<(), String> {
@@ -97,6 +104,7 @@ pub fn run() {
     tauri::Builder::default()
         .invoke_handler(tauri::generate_handler![
             native_host,
+            detect_java,
             validate_manifest,
             inspect_profile,
             sync_profile,

src/main.tsx

@@ -45,6 +45,12 @@ type NativeSettings = {
   memoryMb: number
 }
 
+type JavaInstallation = {
+  executable: string
+  major: number
+  version: string
+}
+
 const servers: Server[] = [
   {
     id: 'aoc',
@@ -76,6 +82,7 @@ function App() {
   const [settingsOpen, setSettingsOpen] = useState(false)
   const [ram, setRam] = useState(6)
   const [nativeHost, setNativeHost] = useState<NativeHost | null>(null)
+  const [java, setJava] = useState<JavaInstallation | null | undefined>(undefined)
 
   useEffect(() => {
     if (progress === null) return
@@ -96,6 +103,9 @@ function App() {
     invoke<NativeSettings>('load_settings')
       .then((settings) => setRam(settings.memoryMb / 1024))
       .catch(() => undefined)
+    invoke<JavaInstallation | null>('detect_java')
+      .then(setJava)
+      .catch(() => setJava(null))
   }, [])
 
   const updateRam = (memoryGb: number) => {
@@ -248,7 +258,22 @@ function App() {
           <input type="range" min="3" max="12" value={ram} onChange={(e) => updateRam(Number(e.target.value))} />
           <small>Для Aeronautics рекомендуется 6 ГБ</small>
         </label>
-        <button className="setting-row"><span><FolderOpen />Папка игры</span><ChevronRight /></button>
+        <div className="setting-row static">
+          <span><FolderOpen />Папка игры</span>
+          <small>{nativeHost ? 'В каталоге лаунчера' : 'Определяется…'}</small>
+        </div>
+        <div className="setting-row static">
+          <span><Wrench />Java</span>
+          <small>
+            {java === undefined
+              ? 'Проверяем…'
+              : java && java.major >= 21
+                ? `Java ${java.major} найдена`
+                : java
+                  ? `Нужна Java 21 · найдена ${java.major}`
+                  : 'Java не найдена'}
+          </small>
+        </div>
         <button className="setting-row"><span><Wrench />Дополнительные параметры</span><ChevronRight /></button>
         <div className="drawer-note">
           {nativeHost ? `Данные лаунчера: ${nativeHost.dataDir}` : 'Java 21 будет управляться лаунчером автоматически.'}

src/styles.css

@@ -141,6 +141,9 @@ button:focus-visible, input:focus-visible { outline: 2px solid var(--green); out
 .setting-row span { display: flex; align-items: center; gap: 11px; font-size: 12px; }
 .setting-row svg { width: 17px; color: #677068; }
 .setting-row:hover { color: white; }
+.setting-row.static { cursor: default; }
+.setting-row.static:hover { color: #abb3ac; }
+.setting-row small { color: #7f8a80; font-size: 11px; }
 .drawer-note { position: absolute; left: 28px; right: 28px; bottom: 26px; padding: 13px 15px; background: #17231a; color: #8fb193; border-radius: 10px; font-size: 10px; }
 
 @media (max-width: 1160px) {