80218: Add BitstreamService#getThumbnail

dspace-api/src/main/java/org/dspace/content/BitstreamServiceImpl.java

@@ -13,6 +13,8 @@ import java.sql.SQLException;
 import java.util.Iterator;
 import java.util.List;
 import java.util.UUID;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import javax.annotation.Nullable;
 
 import org.apache.commons.collections4.CollectionUtils;
@@ -409,6 +411,25 @@ public class BitstreamServiceImpl extends DSpaceObjectServiceImpl<Bitstream> imp
         return null;
     }
 
+    @Override
+    public Bitstream getThumbnail(Context context, Bitstream bitstream) throws SQLException {
+        Pattern pattern = Pattern.compile("^" + bitstream.getName() + ".([^.]+)$");
+
+        for (Bundle bundle : bitstream.getBundles()) {
+            for (Item item : bundle.getItems()) {
+                for (Bundle thumbnails : itemService.getBundles(item, "THUMBNAIL")) {
+                    for (Bitstream thumbnail : thumbnails.getBitstreams()) {
+                        if (pattern.matcher(thumbnail.getName()).matches()) {
+                            return thumbnail;
+                        }
+                    }
+                }
+            }
+        }
+
+        return null;
+    }
+
     @Override
     public BitstreamFormat getFormat(Context context, Bitstream bitstream) throws SQLException {
         if (bitstream.getBitstreamFormat() == null) {

dspace-api/src/main/java/org/dspace/content/service/BitstreamService.java

@@ -209,6 +209,8 @@ public interface BitstreamService extends DSpaceObjectService<Bitstream>, DSpace
 
     public Bitstream getFirstBitstream(Item item, String bundleName) throws SQLException;
 
+    public Bitstream getThumbnail(Context context, Bitstream bitstream) throws SQLException;
+
     public BitstreamFormat getFormat(Context context, Bitstream bitstream) throws SQLException;
 
     public Iterator<Bitstream> findByStoreNumber(Context context, Integer storeNumber) throws SQLException;