As mentioned earlier, MongoDB is currently the top ranked NoSQL database system. (see http://www.kdnuggets.com/2016/06/top-nosql-database-engines.html) It is followed by Apache Cassandra, Redis, Apache HBase, and Neoj4.
MongoDB uses the document data model: a database is a set of collections, each of which is a set of documents, each of which is a set of key-value pairs. Each document is stored as a BSON file.
Cassandra and HBase use the column data model: each data element is a triple: a key, its value, and a timestamp. Cassandra has its own query language, called CQL, that looks like SQL.
Redis uses the key-value data model: a database is a set of dictionaries, each of which is a set of key-value records, where the value is a sequence of fields.
Neoj4 uses the graph data model: a database is a graph whose nodes contain the data. It supports the Cypher query language. Other graph DBS that support Java include GraphBase and OrientDB.
These all have Java APIs, so you can write essentially the same Java access programs that we have used here for our MongoDB database.