feat: add delimiter BlobListOption

google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java

@@ -988,6 +988,16 @@ public static BlobListOption currentDirectory() {
       return new BlobListOption(StorageRpc.Option.DELIMITER, true);
     }
 
+    /**
+     * Returns an option to set a delimiter.
+     *
+     * @param delimiter generally '/' is the one used most often, but you can used other delimiters
+     *     as well.
+     */
+    public static BlobListOption delimiter(String delimiter) {
+      return new BlobListOption(StorageRpc.Option.DELIMITER, delimiter);
+    }
+
     /**
      * Returns an option to define the billing user project. This option is required by buckets with
      * `requester_pays` flag enabled to assign operation costs.

google-cloud-storage/src/main/java/com/google/cloud/storage/StorageImpl.java

@@ -1583,9 +1583,11 @@ private static <T> void addToOptionMap(
       Object prev = temp.put(option.getRpcOption(), option.getValue());
       checkArgument(prev == null, "Duplicate option %s", option);
     }
-    Boolean value = (Boolean) temp.remove(DELIMITER);
-    if (Boolean.TRUE.equals(value)) {
+    if (Boolean.TRUE.equals(temp.get(DELIMITER))) {
+      temp.remove(DELIMITER);
       temp.put(DELIMITER, PATH_DELIMITER);
+    } else if (null != temp.get(DELIMITER)) {
+      temp.put(DELIMITER, temp.get(DELIMITER));
     }
     if (useAsSource) {
       addToOptionMap(IF_GENERATION_MATCH, IF_SOURCE_GENERATION_MATCH, generation, temp);

google-cloud-storage/src/test/java/com/google/cloud/storage/StorageImplTest.java

@@ -1166,6 +1166,23 @@ public void testListBlobsCurrentDirectory() {
     assertArrayEquals(blobList.toArray(), Iterables.toArray(page.getValues(), Blob.class));
   }
 
+  @Test
+  public void testListBlobsDelimiter() {
+    String cursor = "cursor";
+    String delimiter = "/";
+    Map<StorageRpc.Option, ?> options = ImmutableMap.of(StorageRpc.Option.DELIMITER, delimiter);
+    ImmutableList<BlobInfo> blobInfoList = ImmutableList.of(BLOB_INFO1, BLOB_INFO2);
+    Tuple<String, Iterable<com.google.api.services.storage.model.StorageObject>> result =
+        Tuple.of(cursor, Iterables.transform(blobInfoList, BlobInfo.INFO_TO_PB_FUNCTION));
+    EasyMock.expect(storageRpcMock.list(BUCKET_NAME1, options)).andReturn(result);
+    EasyMock.replay(storageRpcMock);
+    initializeService();
+    ImmutableList<Blob> blobList = ImmutableList.of(expectedBlob1, expectedBlob2);
+    Page<Blob> page = storage.list(BUCKET_NAME1, Storage.BlobListOption.delimiter(delimiter));
+    assertEquals(cursor, page.getNextPageToken());
+    assertArrayEquals(blobList.toArray(), Iterables.toArray(page.getValues(), Blob.class));
+  }
+
   @Test
   public void testUpdateBucket() {
     BucketInfo updatedBucketInfo = BUCKET_INFO1.toBuilder().setIndexPage("some-page").build();