Cannot cast BasicDBObject to [B

I have the following gridfs in a mongodb database:

db.outputFs.files.find()

{ "_id" : ObjectId("000000000000000000000001"), "chunkSize" : 261120, "length" : 232, "md5" : "42290309186cc5420acff293b92ae21d", "filename" : "/tmp/outputFs-01.tmp", "contentType" : null, "uploadDate" : ISODate("2015-04-13T13:50:48.259Z"), "aliases" : null, "metadata" : { "estado" : "FICHERO_PDTE_ENVIO", "dataDate" : "20141122", "inputOutputFs" : "output", "gridFileCompression" : "bzip2", "fileType" : "OUTPUT-TEST1", "filePath" : "/tmp/outputFs-01.tmp", "sourceParticipant" : "0100", "destinationParticipant" : "REE", "exportFileName" : "F1_0100_20141122_20150219.0", "processed" : "false", "fileMD5" : "4276e61a4b63d3d1d1b77e27e792bd13", "version" : 0 } }

{ "_id" : ObjectId("000000000000000000000002"), "chunkSize" : 261120, "length" : 232, "md5" : "42290309186cc5420acff293b92ae21d", "filename" : "/tmp/outputFs-02.tmp", "contentType" : null, "uploadDate" : ISODate("2015-04-13T13:50:48.259Z"), "aliases" : null, "metadata" : { "estado" : "FICHERO_ENVIADO_OK", "fechaEnvio" : ISODate("2015-04-13T13:50:48.259Z"), "dataDate" : "20141123", "inputOutputFs" : "output", "gridFileCompression" : "bzip2", "fileType" : "OUTPUT-TEST2", "filePath" : "/tmp/outputFs-02.tmp", "sourceParticipant" : "0100", "destinationParticipant" : "REE", "exportFileName" : "F1_0100_20141123_20150220.0", "processed" : "false", "fileMD5" : "4276e61a4b63d3d1d1b77e27e792bd13", "version" : 0 } }



db.outputFs.chunks.find()

{ "_id" : ObjectId("000000000000000000000001"), "files_id" :  ObjectId("000000000000000000000001"), "n" : 0, "data" : { "$type" : 0, "$binary" : "QlpoOTFBWSZTWZSBQ/YABX5cAAAYQAH/+CAAMAFWA0NqptIb9UgAZ6qowAAFKSaJpGhk8ssmVlk7AAAALZtZZOf0vr859OqflcIs461Dm1skcSOpGpHMuu5HcsJG0j5I9PiR4kaRvvjWskfsVMkZVLxI3uRy/pGTqRj7VmMyTOBfUtb561rwkf0j09+Zbkd+cs1I77861xI7pypvfOt1v5DmR1I51nW7XGdaluRnGZjMzJMzOZGpHnrfGM56+/fnGPVVVVVqqpVVWxCSxCTSAEMkZI3IyqXuqXyRuR/i7kinChISkCh+wA==" } }

{ "_id" : ObjectId("000000000000000000000002"), "files_id" : ObjectId("000000000000000000000002"), "n" : 0, "data" : { "$type" : 0, "$binary" : "QlpoOTFBWSZTWZSBQ/YABX5cAAAYQAH/+CAAMAFWA0NqptIb9UgAZ6qowAAFKSaJpGhk8ssmVlk7AAAALZtZZOf0vr859OqflcIs461Dm1skcSOpGpHMuu5HcsJG0j5I9PiR4kaRvvjWskfsVMkZVLxI3uRy/pGTqRj7VmMyTOBfUtb561rwkf0j09+Zbkd+cs1I77861xI7pypvfOt1v5DmR1I51nW7XGdaluRnGZjMzJMzOZGpHnrfGM56+/fnGPVVVVVqqpVVWxCSxCTSAEMkZI3IyqXuqXyRuR/i7kinChISkCh+wA==" } }

When I try to retrieve it with Spring Data or even MongoChef (both Java clients) as a file, I receive the following error:

com.mongodb.BasicDBObject cannot be cast to [B

The collections were manually imported as they are, not using MongoChef or mongofiles and I have no idea where this error can come from.

Solution

The GridFS specification expects a Binary field called data in the chunks collection. However, your outputFs.chunks does not meet this criteria.

The data field here is not a Binary BSON data type but a regular document that happens to have two fields called $type and $data.

mongoimport will create a Binary field only for JSON entries in the following format. Please note that the order of the fields matters for mongoimport.

{
   "$binary" : ... 
   "$type" : ...
}

Your example has the $type and $binary fields swapped.

Update your JSON file and import your outputFs.chunks again. mongoimport will create valid Binary fields and you'll be able to work with GridFS using your other MongoDB tools.