通过Java驱动程序写入Mongodb。得到以下错误：
com.mongodb.WriteConcernException: { "serverUsed" : "127.0.0.1:27017" , "err" : "_a != -1" , "n" : 0 , "connectionId" : 3 , "ok" : 1.0}
at com.mongodb.CommandResult.getWriteException(CommandResult.java:90)
at com.mongodb.CommandResult.getException(CommandResult.java:79)
at com.mongodb.CommandResult.throwOnError(CommandResult.java:131)
at com.mongodb.DBTCPConnector._checkWriteError(DBTCPConnector.java:135)
at com.mongodb.DBTCPConnector.access$000(DBTCPConnector.java:39)
at com.mongodb.DBTCPConnector$1.execute(DBTCPConnector.java:186)
at com.mongodb.DBTCPConnector$1.execute(DBTCPConnector.java:181)
at com.mongodb.DBTCPConnector.doOperation(DBTCPConnector.java:210)
at com.mongodb.DBTCPConnector.say(DBTCPConnector.java:181)
at com.mongodb.DBCollectionImpl.insertWithWriteProtocol(DBCollectionImpl.java:528)
at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:193)
at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:165)
at com.mongodb.DBCollection.insert(DBCollection.java:161)
at com.mongodb.DBCollection.insert(DBCollection.java:147)
at com.mongodb.DBCollection$insert.call(Unknown Source)
在"err" : "_a != -1"的文档中找不到任何引用。有什么想法吗？
编辑：
添加我使用的代码（并非所有代码都依赖于其他库来解析文件）：
MongoClient mongoClient = new MongoClient()
mongoClient.setWriteConcern(WriteConcern.SAFE)
DB db = mongoClient.getDB("vcf")
List<DBObject> documents = new ArrayList<DBObject>()
DBCollection recordsColl = db.getCollection("records")
//loop through file
BasicDBObject mongoRecord = new BasicDBObject()
//add data to mongoRecord
documents.add(mongoRecord)
//end loop
recordsColl.insert(documents)
mongoClient.close()