DS-4391 Get modified date from the right store

This also tightens up the contract and improves javadocs a bit,
so callers know what to expect.

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

@@ -14,6 +14,8 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.UUID;
 
+import javax.annotation.Nullable;
+
 import org.apache.commons.collections4.CollectionUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.logging.log4j.Logger;
@@ -462,7 +464,9 @@ public class BitstreamServiceImpl extends DSpaceObjectServiceImpl<Bitstream> imp
         return bitstreamDAO.getNotReferencedBitstreams(context);
     }
 
-    public Long getLastModified(Bitstream bitstream) {
+    @Nullable
+    @Override
+    public Long getLastModified(Bitstream bitstream) throws IOException {
         return bitstreamStorageService.getLastModified(bitstream);
     }
 }

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

@@ -14,6 +14,8 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.UUID;
 
+import javax.annotation.Nullable;
+
 import org.dspace.authorize.AuthorizeException;
 import org.dspace.content.Bitstream;
 import org.dspace.content.BitstreamFormat;
@@ -222,5 +224,13 @@ public interface BitstreamService extends DSpaceObjectService<Bitstream>, DSpace
 
     List<Bitstream> getNotReferencedBitstreams(Context context) throws SQLException;
 
-    public Long getLastModified(Bitstream bitstream);
+    /**
+     * Gets the last modified timestamp of the the given bitstream's content, if known.
+     *
+     * @param bitstream the bitstream.
+     * @return the timestamp in milliseconds, or {@code null} if unknown.
+     * @throws IOException if an unexpected io error occurs.
+     */
+    @Nullable
+    Long getLastModified(Bitstream bitstream) throws IOException;
 }

dspace-api/src/main/java/org/dspace/storage/bitstore/BitstreamStorageServiceImpl.java

@@ -16,6 +16,8 @@ import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
+import javax.annotation.Nullable;
+
 import org.apache.commons.collections4.MapUtils;
 import org.apache.logging.log4j.Logger;
 import org.dspace.authorize.AuthorizeException;
@@ -326,15 +328,16 @@ public class BitstreamStorageServiceImpl implements BitstreamStorageService, Ini
         }
     }
 
-    public Long getLastModified(Bitstream bitstream) {
+    @Nullable
-        Map wantedMetadata = new HashMap();
+    @Override
-        wantedMetadata.put("modified", null);
+    public Long getLastModified(Bitstream bitstream) throws IOException {
-        try {
+        Map attrs = new HashMap();
-            wantedMetadata = stores.get(incoming).about(bitstream, wantedMetadata);
+        attrs.put("modified", null);
-        } catch (IOException e) {
+        attrs = stores.get(bitstream.getStoreNumber()).about(bitstream, attrs);
-            log.error(e);
+        if (attrs == null || !attrs.containsKey("modified")) {
+            return null;
         }
-        return Long.valueOf(wantedMetadata.get("modified").toString());
+        return Long.valueOf(attrs.get("modified").toString());
     }
 
     /**

dspace-api/src/main/java/org/dspace/storage/bitstore/service/BitstreamStorageService.java

@@ -12,6 +12,7 @@ import java.io.InputStream;
 import java.sql.SQLException;
 import java.util.Map;
 import java.util.UUID;
+import javax.annotation.Nullable;
 
 import org.dspace.authorize.AuthorizeException;
 import org.dspace.content.Bitstream;
@@ -181,11 +182,13 @@ public interface BitstreamStorageService {
 
 
     /**
-     * Get the last modified timestamp of the file linked to the given bitstream
+     * Gets the last modified timestamp of the the given bitstream's content, if known.
      *
-     * @param bitstream The bitstream for which to get the last modified timestamp
+     * @param bitstream the bitstream.
-     * @return The last modified timestamp in milliseconds
+     * @return the timestamp in milliseconds, or {@code null} if unknown.
+     * @throws IOException if an unexpected io error occurs.
      */
-    public Long getLastModified(Bitstream bitstream);
+    @Nullable
+    Long getLastModified(Bitstream bitstream) throws IOException;
 
 }

dspace-server-webapp/src/main/java/org/dspace/app/rest/BitstreamRestController.java

@@ -140,10 +140,13 @@ public class BitstreamRestController {
                     .withLength(bitstreamTuple.getRight())
                     .withChecksum(bit.getChecksum())
                     .withMimetype(mimetype)
-                    .withLastModified(lastModified)
                     .with(request)
                     .with(response);
 
+            if (lastModified != null) {
+                sender.withLastModified(lastModified);
+            }
+
             //Determine if we need to send the file as a download or if the browser can open it inline
             long dispositionThreshold = configurationService.getLongProperty("webui.content_disposition_threshold");
             if (dispositionThreshold >= 0 && bitstreamTuple.getRight() > dispositionThreshold) {