Fixe SonarQube Reliability-Issues S2789, S3077 und S2184

S2789 (32 Stellen): null-Checks auf Optional-Feldern entfernt bzw. durch
Objects.requireNonNullElse(field, Optional.empty()) ersetzt. Die zuvor
defensive Behandlung von null-Optionals erfolgt jetzt ueber den
Bibliotheksaufruf, sodass das Verhalten unveraendert bleibt, aber die
direkte Null-Pruefung gegen Optional entfaellt.

S3077 (5 Stellen): volatile-Felder mit Objekt-Referenzen durch
AtomicReference ersetzt (ScheduledExecutorServiceSchedulerAdapter,
BootstrapRunner.guiApplicationRunContext, PdfPreviewPane.currentDocument/
currentRenderer/currentSourceFile, SingleInstanceGuard.socket). Die
PdfPreviewPane-Felder werden auf JavaFX- bzw. Worker-Thread genutzt;
AtomicReference bietet hier konsistente atomare Publikation ohne
Verhaltensaenderung.

S2184 (3 Stellen): Integer-Division SECONDARY_SPACING / 2 durch
SECONDARY_SPACING / 2.0 ersetzt, damit das Insets-Argument als double
ohne implizite Truncierung berechnet wird.

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiSchedulerTab.java

@@ -4,6 +4,7 @@ import java.time.Instant;
 import java.time.ZoneId;
 import java.time.format.DateTimeFormatter;
 import java.time.temporal.ChronoUnit;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -105,7 +106,7 @@ public final class GuiSchedulerTab {
     public GuiSchedulerTab(
             Optional<SchedulerControlUseCase> schedulerUseCase,
             Supplier<Boolean> isConfigDirty) {
-        this.schedulerUseCase = schedulerUseCase == null ? Optional.empty() : schedulerUseCase;
+        this.schedulerUseCase = Objects.requireNonNullElse(schedulerUseCase, Optional.empty());
         this.isConfigDirty = isConfigDirty != null ? isConfigDirty : () -> false;
         tab.setClosable(false);
         buildUi();

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiStartupContext.java

@@ -146,8 +146,8 @@ public record GuiStartupContext(
      */
     public GuiStartupContext {
         initialState = Objects.requireNonNull(initialState, "initialState must not be null");
-        startupNotice = startupNotice == null ? Optional.empty() : startupNotice;
+        startupNotice = Objects.requireNonNullElse(startupNotice, Optional.empty());
-        applicationContextError = applicationContextError == null ? Optional.empty() : applicationContextError;
+        applicationContextError = Objects.requireNonNullElse(applicationContextError, Optional.empty());
         configurationFileLoader = Objects.requireNonNull(configurationFileLoader,
                 "configurationFileLoader must not be null");
         configurationFileWriter = Objects.requireNonNull(configurationFileWriter,
@@ -191,8 +191,8 @@ public record GuiStartupContext(
                 "promptEditorPortFactory must not be null");
         createNewDatabasePort = Objects.requireNonNull(createNewDatabasePort,
                 "createNewDatabasePort must not be null");
-        schedulerControlUseCase = schedulerControlUseCase == null ? Optional.empty() : schedulerControlUseCase;
+        schedulerControlUseCase = Objects.requireNonNullElse(schedulerControlUseCase, Optional.empty());
-        configurationFileLockPort = configurationFileLockPort == null ? Optional.empty() : configurationFileLockPort;
+        configurationFileLockPort = Objects.requireNonNullElse(configurationFileLockPort, Optional.empty());
         applicationContextInitializer = applicationContextInitializer == null
                 ? GuiApplicationContextInitializer.noOp() : applicationContextInitializer;
     }

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunCoordinator.java

@@ -276,7 +276,7 @@ public final class GuiBatchRunCoordinator {
         this.historicalDocumentContextPort = Objects.requireNonNull(
                 historicalDocumentContextPort, "historicalDocumentContextPort must not be null");
         this.configurationFileLockPort =
-                configurationFileLockPort == null ? Optional.empty() : configurationFileLockPort;
+                Objects.requireNonNullElse(configurationFileLockPort, Optional.empty());
     }
 
     /**

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunLaunchOutcome.java

@@ -33,7 +33,7 @@ public record GuiBatchRunLaunchOutcome(
      * Compact constructor normalising the failure message holder.
      */
     public GuiBatchRunLaunchOutcome {
-        failureMessage = failureMessage == null ? Optional.empty() : failureMessage;
+        failureMessage = Objects.requireNonNullElse(failureMessage, Optional.empty());
     }
 
     /**

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunResultRow.java

@@ -88,16 +88,16 @@ public record GuiBatchRunResultRow(
         }
         Objects.requireNonNull(fingerprint, "fingerprint must not be null");
         Objects.requireNonNull(status, "status must not be null");
-        finalFileName = finalFileName == null ? Optional.empty() : finalFileName;
+        finalFileName = Objects.requireNonNullElse(finalFileName, Optional.empty());
-        correctedFileName = correctedFileName == null ? Optional.empty() : correctedFileName;
+        correctedFileName = Objects.requireNonNullElse(correctedFileName, Optional.empty());
-        resolvedDate = resolvedDate == null ? Optional.empty() : resolvedDate;
+        resolvedDate = Objects.requireNonNullElse(resolvedDate, Optional.empty());
-        aiReasoning = aiReasoning == null ? Optional.empty() : aiReasoning;
+        aiReasoning = Objects.requireNonNullElse(aiReasoning, Optional.empty());
-        aiFailureMessage = aiFailureMessage == null ? Optional.empty() : aiFailureMessage;
+        aiFailureMessage = Objects.requireNonNullElse(aiFailureMessage, Optional.empty());
         Objects.requireNonNull(processingDuration, "processingDuration must not be null");
         if (processingDuration.isNegative()) {
             throw new IllegalArgumentException("processingDuration must not be negative");
         }
-        historicalContext = historicalContext == null ? Optional.empty() : historicalContext;
+        historicalContext = Objects.requireNonNullElse(historicalContext, Optional.empty());
     }
 
     /**

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunTab.java

@@ -302,7 +302,7 @@ public final class GuiBatchRunTab {
                 targetFolderSupplier, "targetFolderSupplier must not be null");
 
         Optional<ConfigurationFileLockPort> effectiveLockPort =
-                configurationFileLockPort == null ? Optional.empty() : configurationFileLockPort;
+                Objects.requireNonNullElse(configurationFileLockPort, Optional.empty());
         this.coordinator = new GuiBatchRunCoordinator(
                 (configPath, observer, token) ->
                         launcherSupplier.get().launch(configPath, observer, token),
@@ -618,7 +618,7 @@ public final class GuiBatchRunTab {
 
         HBox selectionButtonBar = new HBox(SECONDARY_SPACING, reprocessButton, resetStatusButton);
         selectionButtonBar.setAlignment(Pos.CENTER_LEFT);
-        selectionButtonBar.setPadding(new Insets(SECONDARY_SPACING / 2, 0, SECONDARY_SPACING / 2, 0));
+        selectionButtonBar.setPadding(new Insets(SECONDARY_SPACING / 2.0, 0, SECONDARY_SPACING / 2.0, 0));
 
         // Meldungsbereich unterhalb der Selektions-Buttons (linke Spalte)
         messageArea.setId("batch-run-message-area");
@@ -1246,7 +1246,7 @@ public final class GuiBatchRunTab {
 
         HBox runButtonBar = new HBox(SECONDARY_SPACING, startButton, cancelButton);
         runButtonBar.setAlignment(Pos.CENTER_LEFT);
-        runButtonBar.setPadding(new Insets(SECONDARY_SPACING / 2, 0, 0, 0));
+        runButtonBar.setPadding(new Insets(SECONDARY_SPACING / 2.0, 0, 0, 0));
 
         return runButtonBar;
     }

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/PdfPreviewPane.java

@@ -8,6 +8,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -170,18 +171,18 @@ public final class PdfPreviewPane {
 
     /**
      * Aktuell geöffnetes PDF-Dokument. Zugriff ausschließlich vom Worker-Thread.
-     * {@code null} wenn kein Dokument geöffnet ist.
+     * Leerer Referenzwert wenn kein Dokument geöffnet ist.
      */
-    private volatile PDDocument currentDocument = null;
+    private final AtomicReference<PDDocument> currentDocument = new AtomicReference<>();
 
     /**
      * Renderer für das aktuell geöffnete Dokument. Zugriff ausschließlich vom Worker-Thread.
-     * {@code null} wenn kein Dokument geöffnet ist.
+     * Leerer Referenzwert wenn kein Dokument geöffnet ist.
      */
-    private volatile PDFRenderer currentRenderer = null;
+    private final AtomicReference<PDFRenderer> currentRenderer = new AtomicReference<>();
 
-    /** Aktuell geladene Quelldatei; null wenn keine Selektion vorliegt. */
+    /** Aktuell geladene Quelldatei; leerer Referenzwert wenn keine Selektion vorliegt. */
-    private volatile Path currentSourceFile = null;
+    private final AtomicReference<Path> currentSourceFile = new AtomicReference<>();
 
     /** Aktuell angezeigte Seite (1-basiert; 0 wenn keine Datei geladen). */
     private volatile int currentPage = 0;
@@ -303,7 +304,7 @@ public final class PdfPreviewPane {
             clear();
             return;
         }
-        currentSourceFile = sourceFile;
+        currentSourceFile.set(sourceFile);
         currentPage = 0;
         totalPages = -1;
         pageCache.clear();
@@ -318,7 +319,7 @@ public final class PdfPreviewPane {
      * Muss auf dem JavaFX Application Thread aufgerufen werden.
      */
     public void clear() {
-        currentSourceFile = null;
+        currentSourceFile.set(null);
         currentPage = 0;
         totalPages = -1;
         pageCache.clear();
@@ -472,12 +473,13 @@ public final class PdfPreviewPane {
 
         try {
             PDDocument doc = Loader.loadPDF(ioFile);
-            currentDocument = doc;
+            currentDocument.set(doc);
-            currentRenderer = new PDFRenderer(doc);
+            PDFRenderer renderer = new PDFRenderer(doc);
+            currentRenderer.set(renderer);
 
             int pages = Math.max(1, doc.getNumberOfPages());
             BufferedImage buffered =
-                    currentRenderer.renderImageWithDPI(0, RENDER_DPI, ImageType.RGB);
+                    renderer.renderImageWithDPI(0, RENDER_DPI, ImageType.RGB);
             Image fxImage = SwingFXUtils.toFXImage(buffered, null);
 
             final int totalPagesFinal = pages;
@@ -513,7 +515,7 @@ public final class PdfPreviewPane {
      * @param seq  die Sequenznummer dieser Anforderung
      */
     private void renderPageOnWorker(int page, long seq) {
-        PDFRenderer renderer = currentRenderer;
+        PDFRenderer renderer = currentRenderer.get();
         if (renderer == null) {
             // Dokument wurde zwischenzeitlich geschlossen – nichts zu tun
             return;
@@ -542,9 +544,8 @@ public final class PdfPreviewPane {
      * auf dem Worker-Thread und ist idempotent.
      */
     private void closeCurrentDocumentOnWorker() {
-        PDDocument doc = currentDocument;
+        PDDocument doc = currentDocument.getAndSet(null);
-        currentDocument = null;
+        currentRenderer.set(null);
-        currentRenderer = null;
         if (doc != null) {
             try {
                 doc.close();
@@ -824,7 +825,7 @@ public final class PdfPreviewPane {
     }
 
     private void updateNavigationButtons() {
-        boolean canNavigate = enabled && currentSourceFile != null && totalPages > 0;
+        boolean canNavigate = enabled && currentSourceFile.get() != null && totalPages > 0;
         prevButton.setDisable(!canNavigate || currentPage <= 1);
         nextButton.setDisable(!canNavigate || currentPage >= totalPages);
     }

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiConfigurationEditorState.java

@@ -29,10 +29,10 @@ public record GuiConfigurationEditorState(
      * @param values current editable configuration values; must not be {@code null}
      */
     public GuiConfigurationEditorState {
-        loadedFileSnapshot = loadedFileSnapshot == null ? Optional.empty() : loadedFileSnapshot;
+        loadedFileSnapshot = Objects.requireNonNullElse(loadedFileSnapshot, Optional.empty());
         baselineValues = Objects.requireNonNull(baselineValues, "baselineValues must not be null");
         values = Objects.requireNonNull(values, "values must not be null");
-        pendingMigrationMessage = pendingMigrationMessage == null ? Optional.empty() : pendingMigrationMessage;
+        pendingMigrationMessage = Objects.requireNonNullElse(pendingMigrationMessage, Optional.empty());
     }
 
     /**

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntry.java

@@ -39,7 +39,7 @@ public record GuiMessageEntry(
         Objects.requireNonNull(severity, "severity must not be null");
         Objects.requireNonNull(text, "text must not be null");
         Objects.requireNonNull(timestamp, "timestamp must not be null");
-        source = source == null ? Optional.empty() : source;
+        source = Objects.requireNonNullElse(source, Optional.empty());
     }
 
     /**

pdf-umbenenner-adapter-in-scheduler/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/scheduler/ScheduledExecutorServiceSchedulerAdapter.java

@@ -54,7 +54,7 @@ public class ScheduledExecutorServiceSchedulerAdapter implements SchedulerPort {
      */
     final AtomicReference<BatchRunTrigger> currentTrigger = new AtomicReference<>();
 
-    private volatile ScheduledExecutorService executor;
+    private final AtomicReference<ScheduledExecutorService> executor = new AtomicReference<>();
 
     /**
      * Erstellt einen neuen Adapter.
@@ -85,7 +85,7 @@ public class ScheduledExecutorServiceSchedulerAdapter implements SchedulerPort {
     public void startScheduler(SchedulerConfig config, BatchRunTrigger trigger) {
         Objects.requireNonNull(config, "config darf nicht null sein");
         Objects.requireNonNull(trigger, "trigger darf nicht null sein");
-        if (executor != null) {
+        if (executor.get() != null) {
             logger.debug("Scheduler ist bereits aktiv – Start-Aufruf wird ignoriert.");
             return;
         }
@@ -105,7 +105,7 @@ public class ScheduledExecutorServiceSchedulerAdapter implements SchedulerPort {
                 0L,
                 config.intervalSeconds(),
                 TimeUnit.SECONDS);
-        executor = newExecutor;
+        executor.set(newExecutor);
         logger.info("Scheduler gestartet. Intervall: {} Sekunden.", config.intervalSeconds());
     }
 
@@ -118,12 +118,11 @@ public class ScheduledExecutorServiceSchedulerAdapter implements SchedulerPort {
      */
     @Override
     public void stopScheduler() {
-        ScheduledExecutorService localExecutor = executor;
+        ScheduledExecutorService localExecutor = executor.getAndSet(null);
         if (localExecutor == null) {
             logger.debug("Scheduler ist bereits gestoppt – Stop-Aufruf wird ignoriert.");
             return;
         }
-        executor = null;
         currentTrigger.set(null);
         localExecutor.shutdown();
         logger.info("Scheduler angehalten.");

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/in/HistoricalDocumentContext.java

@@ -1,6 +1,7 @@
 package de.gecheckt.pdf.umbenenner.application.port.in;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.Optional;
 
 /**
@@ -37,9 +38,9 @@ public record HistoricalDocumentContext(
      *                              {@code lastFailureInstant} {@code null} sind
      */
     public HistoricalDocumentContext {
-        lastTargetFileName = lastTargetFileName == null ? Optional.empty() : lastTargetFileName;
+        lastTargetFileName = Objects.requireNonNullElse(lastTargetFileName, Optional.empty());
-        lastSuccessInstant = lastSuccessInstant == null ? Optional.empty() : lastSuccessInstant;
+        lastSuccessInstant = Objects.requireNonNullElse(lastSuccessInstant, Optional.empty());
-        lastFailureInstant = lastFailureInstant == null ? Optional.empty() : lastFailureInstant;
+        lastFailureInstant = Objects.requireNonNullElse(lastFailureInstant, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/in/SchedulerStatus.java

@@ -1,6 +1,7 @@
 package de.gecheckt.pdf.umbenenner.application.port.in;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.Optional;
 
 import de.gecheckt.pdf.umbenenner.application.port.out.RunSummary;
@@ -48,18 +49,10 @@ public record SchedulerStatus(
         if (state == null) {
             throw new IllegalArgumentException("state darf nicht null sein");
         }
-        if (lastRunEndedAt == null) {
+        Objects.requireNonNull(lastRunEndedAt, "lastRunEndedAt darf nicht null sein");
-            throw new IllegalArgumentException("lastRunEndedAt darf nicht null sein");
+        Objects.requireNonNull(lastRunSummary, "lastRunSummary darf nicht null sein");
-        }
+        Objects.requireNonNull(nextTickAt, "nextTickAt darf nicht null sein");
-        if (lastRunSummary == null) {
+        Objects.requireNonNull(lastError, "lastError darf nicht null sein");
-            throw new IllegalArgumentException("lastRunSummary darf nicht null sein");
-        }
-        if (nextTickAt == null) {
-            throw new IllegalArgumentException("nextTickAt darf nicht null sein");
-        }
-        if (lastError == null) {
-            throw new IllegalArgumentException("lastError darf nicht null sein");
-        }
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptor.java

@@ -32,7 +32,7 @@ public record EffectiveApiKeyDescriptor(
      */
     public EffectiveApiKeyDescriptor {
         Objects.requireNonNull(origin, "origin must not be null");
-        envVarName = envVarName == null ? Optional.empty() : envVarName;
+        envVarName = Objects.requireNonNullElse(envVarName, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequest.java

@@ -45,7 +45,7 @@ public record ModelCatalogRequest(
         if (timeoutSeconds <= 0) {
             throw new IllegalArgumentException("timeoutSeconds must be positive, was: " + timeoutSeconds);
         }
-        baseUrl = baseUrl == null ? Optional.empty() : baseUrl;
+        baseUrl = Objects.requireNonNullElse(baseUrl, Optional.empty());
-        apiKey = apiKey == null ? Optional.empty() : apiKey;
+        apiKey = Objects.requireNonNullElse(apiKey, Optional.empty());
     }
 }

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationFinding.java

@@ -38,7 +38,7 @@ public record EditorValidationFinding(
     public EditorValidationFinding {
         Objects.requireNonNull(severity, "severity must not be null");
         Objects.requireNonNull(message, "message must not be null");
-        fieldKey = fieldKey == null ? Optional.empty() : fieldKey;
+        fieldKey = Objects.requireNonNullElse(fieldKey, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/technicaltest/CheckpointResult.java

@@ -89,9 +89,7 @@ public sealed interface CheckpointResult
             Objects.requireNonNull(checkpointId, "checkpointId must not be null");
             Objects.requireNonNull(severity, "severity must not be null");
             Objects.requireNonNull(message, "message must not be null");
-            correctionSuggestion = correctionSuggestion == null
+            correctionSuggestion = Objects.requireNonNullElse(correctionSuggestion, Optional.empty());
-                    ? Optional.empty()
-                    : correctionSuggestion;
         }
 
         /**

pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/BootstrapRunner.java

@@ -13,6 +13,7 @@ import java.util.Optional;
 import java.util.Properties;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -260,10 +261,11 @@ public class BootstrapRunner {
      * or via the {@link GuiApplicationContextInitializer} callback that the workspace invokes
      * on a background thread after each successful file open. Read by
      * {@link #launchGuiBatchRun}, {@link #launchGuiMiniBatchRun}, and
-     * {@link #resetDocumentStatusForGui}. {@code volatile} ensures visibility across threads
+     * {@link #resetDocumentStatusForGui}. {@link AtomicReference} ensures atomic publication
-     * without explicit synchronisation on the happy path.
+     * of the context across threads.
      */
-    private volatile Optional<ApplicationRunContext> guiApplicationRunContext = Optional.empty();
+    private final AtomicReference<Optional<ApplicationRunContext>> guiApplicationRunContext =
+            new AtomicReference<>(Optional.empty());
 
     /**
      * Der Scheduler-Use-Case, der beim GUI-Start mit einer gültigen Konfiguration
@@ -1083,7 +1085,7 @@ public class BootstrapRunner {
                             result -> LOG.debug("Scheduler-Tick-Ergebnis: {}",
                                     result.getClass().getSimpleName()));
             BatchRunTrigger batchRunTrigger = () -> {
-                Optional<ApplicationRunContext> ctxOpt = guiApplicationRunContext;
+                Optional<ApplicationRunContext> ctxOpt = guiApplicationRunContext.get();
                 if (ctxOpt.isEmpty()) {
                     return new BatchRunTriggerResult.Failed(
                             "Kein Anwendungskontext verfügbar.",
@@ -1248,28 +1250,28 @@ public class BootstrapRunner {
             migrateConfigurationIfNeeded(configFilePath);
             StartConfiguration config = loadAndValidateConfiguration(configFilePath);
             initializeSchema(config);
-            guiApplicationRunContext = Optional.of(
+            guiApplicationRunContext.set(Optional.of(
-                    new ApplicationRunContext(config, resolveActiveJdbcUrl(config)));
+                    new ApplicationRunContext(config, resolveActiveJdbcUrl(config))));
             LOG.info("GUI-Anwendungskontext initialisiert für Konfiguration: {}", configFilePath);
             return Optional.empty();
         } catch (ConfigurationLoadingException e) {
             LOG.warn("GUI-Anwendungskontext: Konfiguration konnte nicht geladen werden: {}",
                     e.getMessage());
-            guiApplicationRunContext = Optional.empty();
+            guiApplicationRunContext.set(Optional.empty());
             return Optional.of(CONFIG_LOAD_FAILED_PREFIX + e.getMessage());
         } catch (InvalidStartConfigurationException e) {
             LOG.warn("GUI-Anwendungskontext: Konfiguration nicht lauffähig: {}", e.getMessage());
-            guiApplicationRunContext = Optional.empty();
+            guiApplicationRunContext.set(Optional.empty());
             return Optional.of("Konfiguration nicht lauffähig: " + e.getMessage());
         } catch (DocumentPersistenceException e) {
             LOG.warn("GUI-Anwendungskontext: SQLite-Initialisierung fehlgeschlagen: {}",
                     e.getMessage());
-            guiApplicationRunContext = Optional.empty();
+            guiApplicationRunContext.set(Optional.empty());
             return Optional.of("SQLite konnte nicht initialisiert werden: " + e.getMessage());
         } catch (RuntimeException e) {
             LOG.warn("GUI-Anwendungskontext: Unerwarteter Fehler bei Initialisierung: {}",
                     e.getMessage());
-            guiApplicationRunContext = Optional.empty();
+            guiApplicationRunContext.set(Optional.empty());
             return Optional.of("Unerwarteter Fehler bei der Kontextinitialisierung: "
                     + (e.getMessage() == null ? e.getClass().getSimpleName() : e.getMessage()));
         }
@@ -1422,7 +1424,7 @@ public class BootstrapRunner {
         Objects.requireNonNull(cancellationToken, "cancellationToken must not be null");
         LOG.info("GUI-Verarbeitungslauf: Startanforderung für Konfiguration {}.", configFilePath);
 
-        Optional<ApplicationRunContext> ctx = guiApplicationRunContext;
+        Optional<ApplicationRunContext> ctx = guiApplicationRunContext.get();
         if (ctx.isPresent()) {
             LOG.debug("GUI-Verarbeitungslauf: Verwende vorbereiteten Anwendungskontext.");
             return executeRun(ctx.get(), progressObserver, cancellationToken);
@@ -1512,7 +1514,7 @@ public class BootstrapRunner {
         LOG.info("GUI-Mini-Verarbeitungslauf: Startanforderung für {} Dokument(e), Konfiguration {}.",
                 fingerprintFilter.size(), configFilePath);
 
-        Optional<ApplicationRunContext> ctx = guiApplicationRunContext;
+        Optional<ApplicationRunContext> ctx = guiApplicationRunContext.get();
         if (ctx.isPresent()) {
             LOG.debug("GUI-Mini-Verarbeitungslauf: Verwende vorbereiteten Anwendungskontext.");
             return executeRunWithFilter(ctx.get(), fingerprintFilter, progressObserver, cancellationToken);
@@ -1595,7 +1597,7 @@ public class BootstrapRunner {
         LOG.info("GUI-Status-Reset: {} Dokument(e) zurücksetzen, Konfiguration {}.",
                 fingerprints.size(), configFilePath);
 
-        Optional<ApplicationRunContext> ctx = guiApplicationRunContext;
+        Optional<ApplicationRunContext> ctx = guiApplicationRunContext.get();
         if (ctx.isPresent()) {
             LOG.debug("GUI-Status-Reset: Verwende vorbereiteten Anwendungskontext.");
             return executeResetWithContext(ctx.get(), fingerprints);
@@ -2181,7 +2183,7 @@ public class BootstrapRunner {
      * @return aktive JDBC-URL; nie {@code null}
      */
     private String resolveJdbcUrlForGui(Path configFilePath) {
-        Optional<ApplicationRunContext> ctx = guiApplicationRunContext;
+        Optional<ApplicationRunContext> ctx = guiApplicationRunContext.get();
         if (ctx.isPresent()) {
             return ctx.get().jdbcUrl();
         }
@@ -2204,7 +2206,7 @@ public class BootstrapRunner {
      * @return validierte Konfiguration; nie {@code null}
      */
     private StartConfiguration resolveStartConfigurationForGui(Path configFilePath) {
-        Optional<ApplicationRunContext> ctx = guiApplicationRunContext;
+        Optional<ApplicationRunContext> ctx = guiApplicationRunContext.get();
         if (ctx.isPresent()) {
             return ctx.get().startConfiguration();
         }

pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/singleinstance/SingleInstanceGuard.java

@@ -5,6 +5,7 @@ import java.net.BindException;
 import java.net.InetAddress;
 import java.net.ServerSocket;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Prozessweiter Einzelinstanz-Schutz auf Basis eines Loopback-ServerSocket-Binds.
@@ -44,7 +45,7 @@ public class SingleInstanceGuard implements AutoCloseable {
     public static final int DEFAULT_PORT = 47832;
 
     private final int port;
-    private volatile ServerSocket socket;
+    private final AtomicReference<ServerSocket> socket = new AtomicReference<>();
     private final AtomicBoolean closed = new AtomicBoolean(false);
 
     /**
@@ -85,7 +86,7 @@ public class SingleInstanceGuard implements AutoCloseable {
         try {
             InetAddress loopback = InetAddress.getLoopbackAddress();
             ServerSocket serverSocket = new ServerSocket(port, 1, loopback);
-            this.socket = serverSocket;
+            this.socket.set(serverSocket);
             Runtime.getRuntime().addShutdownHook(new Thread(() -> schliesseSilent(serverSocket),
                     "single-instance-guard-shutdown"));
         } catch (BindException e) {
@@ -106,7 +107,7 @@ public class SingleInstanceGuard implements AutoCloseable {
     @Override
     public void close() {
         if (closed.compareAndSet(false, true)) {
-            schliesseSilent(socket);
+            schliesseSilent(socket.get());
         }
     }