There are a lot of Java SDKs being released by Microsoft these days, and here's another: the Azure Cosmos DB folks have released version 1.0.0 of their asynchronous Java SDK, and at the same time they have open sourced the SDK repo! There is a getting started application ready for people to sink their teeth into, and the artifacts are already up in Maven Central. Finally, the team has released a benchmark tool, and they said to me that they could reach 43,000 document inserts per second (on a 16 CPU core Ubuntu VM) for documents of 1KB size in gateway mode.
For those unfamiliar with Cosmos DB, check out the Azure Cosmos DB introduction. In summary, "Azure Cosmos DB is Microsoft's globally distributed, multi-model database. With the click of a button, Azure Cosmos DB enables you to elastically and independently scale throughput and storage across any number of Azure's geographic regions. It offers throughput, latency, availability, and consistency guarantees with comprehensive service level agreements (SLAs), something no other database service can offer." From there you can find quick start documentation for SQL, MongoDB, Graph, Table, and Cassandra.