JDBM2 介绍
JDBM2 提供了 HashMap 和 TreeMap 的磁盘存储功能，简单易用，用于持久化数据。特别适合用于嵌入到其他应用程序中。示例代码：
/** create (or open existing) database */ String fileName = "helloWorld"; RecordManager recMan = RecordManagerFactory.createRecordManager(fileName); /** Creates TreeMap which stores data in database. * Constructor method takes recordName (something like SQL table name)*/ String recordName = "firstTreeMap"; PrimaryTreeMap treeMap = recMan.treeMap(recordName); /** add some stuff to map*/ treeMap.put(1, "One"); treeMap.put(2, "Two"); treeMap.put(3, "Three"); System.out.println(treeMap.keySet()); // > [1, 2, 3] /** Map changes are not persisted yet, commit them (save to disk) */ recMan.commit(); System.out.println(treeMap.keySet()); // > [1, 2, 3] /** Delete one record. Changes are not commited yet, but are visible. */ treeMap.remove(2); System.out.println(treeMap.keySet()); // > [1, 3] /** Did not like change. Roolback to last commit (undo record remove). */ recMan.rollback(); /** Key 2 was recovered */ System.out.println(treeMap.keySet()); // > [1, 2, 3] /** close record manager */ recMan.close();