Persisting Java objects is now easy.

Transparent persistence. Powerful querying.

Use the API your prefer, to a very wide range of datastores.

The most standards-compliant Java persistence product.

Open Source software, under the Apache 2 license
Choose Your API
Java Data Objects (JDO)

Java standard since 2001, providing transparent persistence and datastore agnosticity. Comes with its own "Java syntax" JDOQL query language so you can use the Java syntax you already know to query your data. Supports JDO3.1
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Java Persistence API (JPA)

Java standard since 2006, providing easy persistence to RDBMS datastores. Comes with its own "SQL-like" JPQL query language, so you query your data in a language similar to what your datastore understands. Supports JPA2.1
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REST API (JSON)

For web-based applications where you want to request objects from a server, and post object updates to the server and be able to retrieve those objects at a later date.
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Choose Your Datastore
RDBMS Relational databases like PostgreSQL, MySQL, Oracle, SQLServer, DB2, H2 etc have been the database workhorses since the 1980s and won't be going away anytime soon. Data is stored relationally, consisting of tables and columns, and can be indexed for faster access, with foreign keys assigned to provide relational integrity of data. Data is queried using Structured Query Language (SQL).
Map-Based HBase and Cassandra store data in a map-type structure. Data is queried using their own language.
Graph-Based Neo4j stores data in a graph structure, perfect for allowing navigation between objects.
Documents Spreadsheets like Excel and LibreOffice store their data in XLS, OOXML and ODF formats. You can persist your data in this format too so that it is easily interchangeable with other parts of your organisation. XML is a standard document format for interchanging data, and can also be used for storage of data.
Web-based Amazon S3 and Google Storage allow data to be stored in essentially "JSON" format, ready to pass around the web via REST.
Doc-based MongoDB stores its data in document structures, utilising a JSON-style, so hence web-accessible, yet also very flexible in terms of querying.
Others LDAP is a vendor-neutral standard for accessing/maintaining distributed directory services information, such as account information.
Documentation
Browse our extensive documentation for recent versions of DataNucleus AccessPlatform. Explore the different APIs and features available for each datastore.
Version 4.0 : Browse Online | PDF
Version 4.1 : Browse Online | PDF
Download
Download the latest version as a convenient ZIP file with all dependencies : Version 4.0 | Version 4.1
Contribute
Explore the codebase on GitHub and contribute new features or fix bugs We have made all code available under the very flexible Apache 2 License so you have every opportunity to offer your skills to the project.
Keep up to date
Follow the DataNucleus blog or Twitter (@datanucleus). You can receive updates when features are added, or bugs are fixed that could impact on your application(s).