8364768: JDK javax.imageio ImageWriters do not all flush the output stream

src/java.desktop/share/classes/com/sun/imageio/plugins/gif/GIFImageWriter.java

@@ -734,6 +734,7 @@ private void write(boolean writeHeader,
         if (writeTrailer) {
             writeTrailer();
         }
+        stream.flush();
     }
 
     /**

src/java.desktop/share/classes/com/sun/imageio/plugins/tiff/TIFFImageWriter.java

@@ -2327,6 +2327,7 @@ public void write(IIOMetadata sm,
         if (abortRequested()) {
             resetPositions();
         }
+        stream.flush();
     }
 
     private void writeHeader() throws IOException {

test/jdk/javax/imageio/FlushTest.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8364768
+ * @summary Tests that the standard plugins flush the stream after writing a complete image.
+ */
+
+import static java.awt.Color.WHITE;
+import java.awt.Graphics2D;
+import java.awt.image.BufferedImage;
+import java.io.IOException;
+import java.io.ByteArrayOutputStream;
+import javax.imageio.ImageIO;
+import javax.imageio.ImageWriter;
+import javax.imageio.stream.FileCacheImageOutputStream;
+
+public class FlushTest {
+
+    static final int SZ = 1000;
+    static BufferedImage bi;
+    static final String[] FORMATS = { "jpg", "png", "gif", "tiff", "bmp", "wbmp" } ;
+    static boolean failed = false;
+
+    public static void main(String[] args) throws IOException {
+
+        bi = new BufferedImage(SZ, SZ, BufferedImage.TYPE_BYTE_BINARY);
+        Graphics2D g2d = bi.createGraphics();
+        g2d.setPaint(WHITE);
+        g2d.fillRect(0, 0, SZ, SZ);
+
+        for (String f : FORMATS) {
+            testWrite(f);
+        }
+        if (failed) {
+           throw new RuntimeException("Stream sizes differ.");
+        }
+    }
+
+    static void testWrite(String fmt) throws IOException {
+        ImageWriter iw = ImageIO.getImageWritersBySuffix(fmt).next();
+        System.out.println(iw);
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        FileCacheImageOutputStream fcs = new FileCacheImageOutputStream(baos, null);
+        iw.setOutput(fcs);
+        iw.write(bi);
+        int sz0 = baos.size();
+        fcs.close();
+        int sz1 = baos.size();
+        System.out.println("fmt=" + fmt + " sizes=" + sz0 + ", " + sz1);
+        if (sz0 != sz1) {
+           failed = true;
+        }
+    }
+}