feat: support cancelling queued downloads if the UI is closed

src/main/java/com/flowingcode/vaadin/addons/gridexporter/ConcurrentStreamResourceWriter.java

@@ -1,11 +1,13 @@
 package com.flowingcode.vaadin.addons.gridexporter;
 
+import com.vaadin.flow.component.UI;
 import com.vaadin.flow.server.StreamResourceWriter;
 import com.vaadin.flow.server.VaadinSession;
 import java.io.IOException;
 import java.io.InterruptedIOException;
 import java.io.OutputStream;
 import java.nio.channels.InterruptedByTimeoutException;
+import java.util.Optional;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
 import java.util.function.IntFunction;
@@ -30,6 +32,8 @@ abstract class ConcurrentStreamResourceWriter implements StreamResourceWriter {
 
   private static volatile boolean enabled;
 
+  private static volatile boolean failOnUiChange;
+
   private final StreamResourceWriter delegate;
 
   private static final class ConfigurableSemaphore extends Semaphore {
@@ -89,6 +93,10 @@ public static void setLimit(float limit) {
     }
   }
 
+  static void setFailOnUiChange(boolean failOnUiChange) {
+    ConcurrentStreamResourceWriter.failOnUiChange = failOnUiChange;
+  }
+
   /**
    * Returns the limit for the number of concurrent downloads.
    *
@@ -147,6 +155,22 @@ public float getCost(VaadinSession session) {
     return DEFAULT_COST;
   }
 
+  /**
+   * Returns the UI associated with the current download.
+   * <p>
+   * This method is used to ensure that the UI is still attached to the current session when a
+   * download is initiated. Implementations should return the appropriate UI instance.
+   * </p>
+   *
+   * @return the {@link UI} instance associated with the current download, or {@code null} if no UI
+   *         is available.
+   */
+  protected abstract UI getUI();
+
+  private UI getAttachedUI() {
+    return Optional.ofNullable(getUI()).filter(UI::isAttached).orElse(null);
+  }
+
   /**
    * Callback method that is invoked when a timeout occurs while trying to acquire a permit for
    * starting a download.
@@ -207,36 +231,41 @@ public float getCost(VaadinSession session) {
   public final void accept(OutputStream stream, VaadinSession session) throws IOException {
     onAccept();
     try {
-      if (!enabled) {
-        delegate.accept(stream, session);
-      } else {
+    if (!enabled) {
+      delegate.accept(stream, session);
+    } else {
 
-        try {
+      try {
+        int permits;
+        float cost = getCost(session);
+        synchronized (semaphore) {
+          permits = costToPermits(cost, semaphore.maxPermits);
+        }
 
-          int permits;
-          float cost = getCost(session);
-          synchronized (semaphore) {
-            permits = costToPermits(cost, semaphore.maxPermits);
-          }
+        UI ui = failOnUiChange ? getAttachedUI() : null;
 
-          if (semaphore.tryAcquire(permits, getTimeout(), TimeUnit.NANOSECONDS)) {
-            try {
-              delegate.accept(stream, session);
-            } finally {
-              semaphore.release(permits);
+        if (semaphore.tryAcquire(permits, getTimeout(), TimeUnit.NANOSECONDS)) {
+          try {
+            if (ui != null && getAttachedUI()!=ui) {
+              // The UI has changed or was detached after acquirig the semaphore
+              throw new IOException("Detached UI");
             }
-          } else {
-            onTimeout();
-            throw new InterruptedByTimeoutException();
+            delegate.accept(stream, session);
+          } finally {
+            semaphore.release(permits);
           }
-        } catch (InterruptedException e) {
-          Thread.currentThread().interrupt();
-          throw (IOException) new InterruptedIOException().initCause(e);
+        } else {
+          onTimeout();
+          throw new InterruptedByTimeoutException();
         }
+      } catch (InterruptedException e) {
+        Thread.currentThread().interrupt();
+        throw (IOException) new InterruptedIOException().initCause(e);
       }
+    }
     } finally {
       onFinish();
-    }
+  }
   }
 
 }

src/main/java/com/flowingcode/vaadin/addons/gridexporter/GridExporter.java

@@ -24,6 +24,7 @@
 import com.vaadin.flow.component.Component;
 import com.vaadin.flow.component.ComponentUtil;
 import com.vaadin.flow.component.HasEnabled;
+import com.vaadin.flow.component.UI;
 import com.vaadin.flow.component.grid.ColumnPathRenderer;
 import com.vaadin.flow.component.grid.Grid;
 import com.vaadin.flow.component.grid.Grid.Column;
@@ -41,6 +42,7 @@
 import com.vaadin.flow.server.StreamResourceWriter;
 import com.vaadin.flow.server.VaadinSession;
 import com.vaadin.flow.shared.Registration;
+import java.io.IOException;
 import java.io.Serializable;
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
@@ -354,27 +356,32 @@ private class GridExporterConcurrentStreamResourceWriter extends ConcurrentStrea
 
     private Component button;
 
-    @Override
-    public float getCost(VaadinSession session) {
-      return concurrentDownloadCost;
-    }
+      @Override
+      public float getCost(VaadinSession session) {
+        return concurrentDownloadCost;
+      }
 
-    @Override
-    public long getTimeout() {
-      // It would have been possible to specify a different timeout for each instance but I cannot
-      // figure out a good use case for that. The timeout returned herebecomes relevant when the
-      // semaphore has been acquired by any other download, so the timeout must reflect how long
-      // it is reasonable to wait for "any other download" to complete and release the semaphore.
-      //
-      // Since the reasonable timeout would depend on the duration of "any other download", it
-      // makes sense that it's a global setting instead of a per-instance setting.
-      return concurrentDownloadTimeoutNanos;
-    }
+      @Override
+      public long getTimeout() {
+        // It would have been possible to specify a different timeout for each instance but I cannot
+        // figure out a good use case for that. The timeout returned herebecomes relevant when the
+        // semaphore has been acquired by any other download, so the timeout must reflect how long
+        // it is reasonable to wait for "any other download" to complete and release the semaphore.
+        //
+        // Since the reasonable timeout would depend on the duration of "any other download", it
+        // makes sense that it's a global setting instead of a per-instance setting.
+        return concurrentDownloadTimeoutNanos;
+      }
 
-    @Override
-    protected void onTimeout() {
-      fireConcurrentDownloadTimeout();
-    }
+      @Override
+      protected UI getUI() {
+        return grid.getUI().orElse(null);
+      }
+
+      @Override
+      protected void onTimeout() {
+        fireConcurrentDownloadTimeout();
+      }
 
     @Override
     protected void onAccept() {
@@ -386,7 +393,7 @@ protected void onAccept() {
     @Override
     protected void onFinish() {
       setButtonEnabled(true);
-    }
+  }
 
     private void setButtonEnabled(boolean enabled) {
       if (button instanceof HasEnabled) {
@@ -474,9 +481,20 @@ public static float getConcurrentDownloadLimit() {
     return ConcurrentStreamResourceWriter.getLimit();
   }
 
+  /**
+   * Configures the behavior of the stream operation when the UI changes during execution.
+   *
+   * @param failOnUiChange If {@code true}, the operation will throw an {@link IOException} if the
+   *        UI changes (e.g., becomes detached) after acquiring the semaphore. If {@code false}, the
+   *        operation will proceed regardless of any UI changes.
+   */
+  public static void setFailOnUiChange(boolean failOnUiChange) {
+    ConcurrentStreamResourceWriter.setFailOnUiChange(failOnUiChange);
+  }
+
   /**
    * Sets the timeout for acquiring a permit to start a download when the
-   * {@linkplain #setConcurrentDownloadLimit(int) maximum number of concurrent downloads} is
+   * {@linkplain #setConcurrentDownloadLimit(float) maximum number of concurrent downloads} is
    * reached. If the timeout is less than or equal to zero, the downloads will fail immediately if
    * no enough permits can be acquired.
    *
@@ -669,7 +687,7 @@ public void setExportValue(Column<T> column, ValueProvider<T, ?> vp) {
    * Configure if the column is exported or not
    *
    * @param column
-   * @param export: true will be included in the exported file, false will not be included
+   * @param export true will be included in the exported file, false will not be included
    */
   public void setExportColumn(Column<T> column, boolean export) {
     ComponentUtil.setData(column, COLUMN_EXPORTED_PROVIDER_DATA, export);
@@ -737,7 +755,7 @@ public void setDateColumnFormat(Column<T> column, DateFormat dateFormat, String
    *
    * @param column
    * @param dateFormat
-   * @param excelFormat
+   * @param excelFormatProvider
    */
   public void setDateColumnFormatProvider(Column<T> column, DateFormat dateFormat,
       ValueProvider<T, String> excelFormatProvider) {
@@ -820,8 +838,6 @@ public List<Column<T>> getColumns() {
 
   /**
    * Get columns in the positions specified by {@link GridExporter.setColumnPosition}
-   *
-   * @return
    */
   public List<Column<T>> getColumnsOrdered() {
     return columns == null

src/test/java/com/flowingcode/vaadin/addons/gridexporter/ConfigurableConcurrentStreamResourceWriter.java

@@ -1,5 +1,6 @@
 package com.flowingcode.vaadin.addons.gridexporter;
 
+import com.vaadin.flow.component.UI;
 import com.vaadin.flow.server.StreamResourceWriter;
 import com.vaadin.flow.server.VaadinSession;
 
@@ -13,6 +14,7 @@ public ConfigurableConcurrentStreamResourceWriter(StreamResourceWriter delegate)
 
   private float cost = GridExporter.DEFAULT_COST;
   private long timeout = 0L;
+  private UI ui;
 
   @Override
   public float getCost(VaadinSession session) {
@@ -32,4 +34,13 @@ public void setTimeout(long timeout) {
     this.timeout = timeout;
   }
 
+  @Override
+  public UI getUI() {
+    return ui;
+  }
+
+  public void setUi(UI ui) {
+    this.ui = ui;
+  }
+
 }

src/test/java/com/flowingcode/vaadin/addons/gridexporter/VaadinServiceInitListenerImpl.java

@@ -20,6 +20,8 @@ public void serviceInit(ServiceInitEvent event) {
     });
     // end-block
 
+    GridExporter.setFailOnUiChange(true);
+
   }
 
 }