JDBM中提供了一个接口RecordManager，用于对记录进行操作：

  public abstract long insert( Object obj )
        throws IOException;

   
    /**
     *  Inserts a new record using a custom serializer.
     */
    public abstract long insert( Object obj, Serializer serializer )
        throws IOException;

    /**
     *  Deletes a record.
     */
    public abstract void delete( long recid )
        throws IOException;

    /**
     *  Updates a record using standard java object serialization.
     */
    public abstract void update( long recid, Object obj )
        throws IOException;

    /**
     *  Updates a record using a custom serializer.
     */
    public abstract void update( long recid, Object obj, Serializer serializer )
        throws IOException;

   
    /**
     *  Fetches a record using standard java object serialization.
     */
    public abstract Object fetch( long recid )
        throws IOException;

    /**
     *  Fetches a record using a custom serializer.
     */
    public abstract Object fetch( long recid, Serializer serializer )
        throws IOException;

    /**
     *  Closes the record manager.
     */
    public abstract void close()
        throws IOException;

具体的实现类一共两个：BaseRecordManager和CacheRecordManager，后者是前者的Cache。BaseRecordManager用于将缓存对象序列化到文件系统中，即缓存对象管理主要是文件读取方面的操作，而CacheRecordManager
对读取的文件进行了缓存，较少IO的次数提高效率。

BaseRecordManager

BaseRecordManager有四个主要的变量

    /**
     * Underlying record file.
     */
    private RecordFile _file;
    /**
     * Physical row identifier manager.
     */
    private PhysicalRowIdManager _physMgr;
    /**
     * Logigal to Physical row identifier manager.
     */
    private LogicalRowIdManager _logMgr;
    /**
     * Page manager.
     */
    private PageManager _pageman;

没有看其实现代码，但是从其构造函数可以看出一些端倪：
    public BaseRecordManager( String filename )
        throws IOException
    {
        _file = new RecordFile( filename );
        _pageman = new PageManager( _file );
        _physMgr = new PhysicalRowIdManager( _file, _pageman );
        _logMgr = new LogicalRowIdManager( _file, _pageman );
    }
jdbm.recman主要都是关于Page,PhysicalRow和LogicalRow这些相关类。