其实我们要的是内存数据库引擎，就是暴露给我们的是JDBC的API，我们就像操作数据库一样的操作，但是数据并没有写入磁盘，而是在内存中。当然需要持久化时，你也可以把它写入磁盘。
HSQLDB是这样一个实现，它是一个数据库引擎，可以作为嵌入式的数据库，也可以作为内存数据库。并且在很多知名的项目中已经有了应用比如openOffice。
我们应该关注一下！
http://hsqldb.sourceforge.net/
HSQLDB is the leading SQL relational database engine written in Java. It has a JDBC driver and supports a rich subset of ANSI-92 SQL (BNF tree format) plus SQL 99 and 2003 enhancements. It offers a small (less than 100k in one version), fast database engine which offers both in-memory and disk-based tables. Embedded and server modes are available. Additionally, it includes tools such as a minimal web server, in-memory query and management tools (can be run as applets) and a number of demonstration examples.
The product is currently being used as a database and persistence engine in many Open Source Software projects and even in commercial projects and products. In it's current version it is extremely stable and reliable. It is best known for its small size, ability to execute completely in memory and its speed.
This feature-packed software is completely free under our licenses , based on the standard BSD license. Yes, that's right, completely free of cost or onerous restrictions and fully compatible with all major open source licenses. Java source code and extensive documentation always included!
Users please visit the Project Summary Page for more information and to submit Patches, Bugs, Feature Requests and communicate with the Project Team or view/browse/subscribe to one or more of our mailing lists.
Also visit our pages featuring HSQLDB for the Sharp Zaurus platform, a special version with a data entry and view interface.
Developers please visit the Developers Page and join our effort!
Our group was formed in 2001 and has as its charter the continuation of Thomas Mueller's closed Hypersonic SQL Project. We have actively developed and released six new versions of the database since April 2001. The latest release version features a wide range of new functionality and code rewrite. The project enjoys an overall ranking of 82 among all SourceForege projects (85,000) with over 380,000 downloads.
The last stable code from Thomas' project (Hypersonic SQL version 1.43) is also available for download at Thomas Mueller's Hypersonic SQL page at SourceForge.