perf: optimize Java Language Server startup time

Reduce startup time from ~72s to ~49ms by eliminating unnecessary
subprocess calls, system scans, and disk I/O on the critical path:

- Read JDK release file instead of spawning java -version subprocess
  in getMajorVersion() (was ~33s per call)
- Skip listJdks() system scan in resolveRequirements when toolingJre
  is valid - defer JDK discovery after server startup via
  didChangeConfiguration notification (was ~16s)
- Defer addAutoDetectedJdks in getJavaConfig until after server start
  by adding skipAutoDetection parameter
- Use context.extension.packageJSON.version instead of reading and
  parsing package.json from disk in getVersion() (3 calls at startup)

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

src/extension.ts

@@ -224,7 +224,7 @@ export async function activate(context: ExtensionContext): Promise<ExtensionAPI>
 	const requireStandardServer = (serverMode !== ServerMode.lightWeight) && (!isDebugModeByClientPort || !!process.env['JDTLS_CLIENT_PORT']);
 	let initFailureReported: boolean = false;
 
-	const javaConfig = await getJavaConfig(requirementsData.java_home);
+	const javaConfig = await getJavaConfig(requirementsData.java_home, true);
 	javaConfigDeferred.resolve(javaConfig);
 
 	// Options to control the language client
@@ -790,6 +790,12 @@ async function doStartStandardServer(context: ExtensionContext, requirements: re
 	await standardClient.initialize(context, requirements, clientOptions, workspacePath, jdtEventEmitter);
 	standardClient.start().then(async () => {
 		standardClient.registerLanguageClientActions(context, await fse.pathExists(path.join(workspacePath, ".metadata", ".plugins")), jdtEventEmitter);
+		// Send auto-detected JDKs after server startup to avoid blocking initialization
+		standardClient.getClient().sendNotification(DidChangeConfigurationNotification.type, {
+			settings: {
+				java: await getJavaConfig(requirements.java_home),
+			}
+		});
 	});
 	serverStatusBarProvider.setBusy("Activating...");
 	return standardClient.getClient();
@@ -1269,7 +1275,7 @@ async function cleanJavaWorkspaceStorage() {
 }
 
 async function cleanOldGlobalStorage(context: ExtensionContext) {
-	const currentVersion = getVersion(context.extensionPath);
+	const currentVersion = getVersion(context);
 	const globalStoragePath = context.globalStorageUri?.fsPath; // .../Code/User/globalStorage/redhat.java
 
 	ensureExists(globalStoragePath);

src/javaServerStarter.ts

@@ -297,7 +297,7 @@ function prepareParams(requirements: RequirementsData, workspacePath, context: E
 		}
 
 		const hasJDWP = params.find((param: string) => param.includes('jdwp')) !== undefined;
-		const extVersion = getVersion(context.extensionPath);
+		const extVersion = getVersion(context);
 		const globalStoragePath = path.resolve(context.globalStorageUri?.fsPath, extVersion); // .../Code/User/globalStorage/redhat.java/1.42.0/
 		const appCDSMode = workspace.getConfiguration().get('java.jdt.ls.appcds.enabled');
 		const useAppCDS = (appCDSMode === 'on') || (appCDSMode === 'auto' && (isPrereleaseOrInsiderVersion(context)));
@@ -396,7 +396,7 @@ export function getSharedIndexCache(context: ExtensionContext): string {
 
 function resolveConfiguration(context, configDir) {
 	ensureExists(context.globalStoragePath);
-	const version = getVersion(context.extensionPath);
+	const version = getVersion(context);
 	let configuration = path.resolve(context.globalStoragePath, version);
 	ensureExists(configuration);
 	configuration = path.resolve(configuration, configDir);

src/jdkUtils.ts

@@ -3,7 +3,7 @@
 import { existsSync } from 'fs';
 import { IJavaRuntime, findRuntimes, getSources } from 'jdk-utils';
 import { join } from 'path';
-import { ExtensionContext, Uri, workspace } from 'vscode';
+import { ExtensionContext } from 'vscode';
 
 let cachedJdks: IJavaRuntime[];
 let cachedJreNames: string[];
@@ -14,8 +14,7 @@ export async function loadSupportedJreNames(context: ExtensionContext): Promise<
 }
 
 async function getContributesConfiguration(context: ExtensionContext, configId: string): Promise<any> {
-	const buffer = await workspace.fs.readFile(Uri.file(context.asAbsolutePath("package.json")));
-	const packageJson = JSON.parse(buffer.toString());
+	const packageJson = context.extension.packageJSON;
 	/**
 	 * contributes.configuration can either be a single object,
 	 * representing a single category of settings, or an array

src/requirements.ts

@@ -2,7 +2,7 @@
 
 import expandHomeDir from 'expand-home-dir';
 import * as fse from 'fs-extra';
-import { getRuntime, getSources, JAVAC_FILENAME, JAVA_FILENAME } from 'jdk-utils';
+import { getRuntime, JAVAC_FILENAME, JAVA_FILENAME } from 'jdk-utils';
 import * as path from 'path';
 import { env, ExtensionContext, Uri, window, workspace } from 'vscode';
 import { Commands } from './commands';
@@ -74,10 +74,10 @@ export async function resolveRequirements(context: ExtensionContext): Promise<Re
             }
         }
 
-        // search valid JDKs from env.JAVA_HOME, env.PATH, SDKMAN, jEnv, jabba, Common directories
-        const javaRuntimes = await listJdks();
         if (!toolingJre) { // universal version
+            // search valid JDKs from env.JAVA_HOME, env.PATH, SDKMAN, jEnv, jabba, Common directories
             // as latest version as possible.
+            const javaRuntimes = await listJdks();
             sortJdksByVersion(javaRuntimes);
             const validJdks = javaRuntimes.filter(r => r.version.major >= REQUIRED_JDK_VERSION);
             if (validJdks.length > 0) {
@@ -99,16 +99,12 @@ export async function resolveRequirements(context: ExtensionContext): Promise<Re
              */
             if (javaHome) {
                 logger.info(`Use the JDK from '${preferenceName}' setting as the initial default project JDK.`);
-            } else if (javaRuntimes.length) {
-                sortJdksBySource(javaRuntimes);
-                javaHome = javaRuntimes[0].homedir;
-                javaVersion = javaRuntimes[0].version?.major;
-                logger.info(`Use the JDK from '${getSources(javaRuntimes[0])}' as the initial default project JDK.`);
             } else if (javaHome = await findDefaultRuntimeFromSettings()) {
                 javaVersion = await getMajorVersion(javaHome);
                 logger.info("Use the JDK from 'java.configuration.runtimes' as the initial default project JDK.");
             } else {
-                openJDKDownload(reject, "Please download and install a JDK to compile your project. You can configure your projects with different JDKs by the setting ['java.configuration.runtimes'](https://github.com/redhat-developer/vscode-java/wiki/JDK-Requirements#java.configuration.runtimes)");
+				javaHome = toolingJre;
+                javaVersion = toolingJreVersion;
             }
         }
 

src/utils.ts

@@ -220,7 +220,7 @@ function getDirectoriesByBuildFile(inclusions: string[], exclusions: string[], f
 
 const detectJdksAtStart: boolean = getJavaConfiguration().get<boolean>('configuration.detectJdksAtStart');
 
-export async function getJavaConfig(javaHome: string) {
+export async function getJavaConfig(javaHome: string, skipAutoDetection?: boolean) {
 	const origConfig = getJavaConfiguration();
 	const javaConfig = JSON.parse(JSON.stringify(origConfig));
 	javaConfig.home = javaHome;
@@ -274,7 +274,7 @@ export async function getJavaConfig(javaHome: string) {
 	}
 
 	javaConfig.telemetry = { enabled: workspace.getConfiguration('redhat.telemetry').get('enabled', false) };
-	if (detectJdksAtStart) {
+	if (detectJdksAtStart && !skipAutoDetection) {
 		const userConfiguredJREs: any[] = javaConfig.configuration.runtimes;
 		javaConfig.configuration.runtimes = await addAutoDetectedJdks(userConfiguredJREs);
 	}
@@ -344,14 +344,8 @@ export function resolveActualCause(callstack: any): any {
 	return callstack;
 }
 
-export function getVersion(extensionPath: string): string {
-	const packagePath = path.resolve(extensionPath, "package.json");
-	const packageFile = JSON.parse(fs.readFileSync(packagePath, 'utf8'));
-	if (packageFile) {
-		return packageFile.version;
-	}
-
-	return '0.0.0';
+export function getVersion(context: ExtensionContext): string {
+	return context.extension.packageJSON?.version || '0.0.0';
 }
 
 export function getVSCodeVariablesMap(): any {
@@ -368,19 +362,18 @@ export function getVSCodeVariablesMap(): any {
  * @param context The extension context or extension path
  * @returns true if the version is a pre-release version or running an insider editor
  */
-export function isPrereleaseOrInsiderVersion(context: ExtensionContext | string): boolean {
+export function isPrereleaseOrInsiderVersion(context: ExtensionContext): boolean {
 	return  isInsiderEditor() || isPreReleaseVersion(context);
 }
 
 /**
  * Check if the extension version is a pre-release version.
  * Pre-release versions follow the pattern: major.minor.timestamp (e.g., 1.47.1234567890)
- * @param context The extension context or extension path
+ * @param context The extension context
  * @returns true if the version is a pre-release version
  */
-export function isPreReleaseVersion(context: ExtensionContext | string): boolean {
-	const extensionPath = typeof context === 'string' ? context : context.extensionPath;
-	const extVersion = getVersion(extensionPath);
+export function isPreReleaseVersion(context: ExtensionContext): boolean {
+	const extVersion = getVersion(context);
 	return /^\d+\.\d+\.\d{10}/.test(extVersion);
 }