com.coyotegulch.jisp
public class ObjectDatabaseFile extends Object
ObjectDatabaseFile
provides a random-access file that
serializes objects to variable length records in a random-access file.
An ObjectDatabaseFile
allows the deletion of records and
automatically uses such space for new records.
For the purposes of an ObjectDatabaseFile
, consider record
and object to be synonyms. In traditional database terms, an
ObjectDatabaseFile
is a table, each object is a row,
and each field in an object is a column. Unlike a full-featured
database, an ObjectDatabaseFile
can contain a set of heterogenous
records -- in other words, different objects can be stored together in one
ObjectDatabaseFile
. This class is the foundation of the Jisp
package, providing the fundamental file structures for both indexes and data
files.
You can store any serializable object in an ObjectDatabaseFile
.
Records in an ObjectDatabaseFile
can have varying lengths based
on the serialization requirements of objects. To handle variable-length records,
a ObjectDatabaseFile
records the size of each record. When a record
is deleted, the space it occupied is marked as empty; the files maintains a
linked list of deleted record locations and thier sizes.
Inserting a new record involves a traverse of the deleted list, looking for an empty record that is large enough to contain the new information. If the deleted list is empty, or the new record is too large to fit into any open slots, the new object record is appended to the file.
Reusing deleted record space has a drawback: it leaves dead space in the file when
a newly-inserted record is smaller than the "deleted" space it
overwrites. Deleted records also use space in the file until a new record is
written into their location. Periodically, it makes sense to compact the
file, removing the wasted space and eliminating deleted records. ObjectDatabaseFile
recovers "waste space" by re-writing the file, record by record, using exact record lengths,
ignoring deleted records, and calling a user-provided method so that indexes can be
simultaneously regenerated.
See Also: IndexedObjectDatabase PageDatabaseFile
Field Summary | |
---|---|
protected static long | DEL_LIST_END
Marks the end of the list of deleted records |
protected static byte | IS_ACTIVE
Marks a given record as containing live data |
protected static byte | IS_DELETED
Marks a given record as deleted |
protected RandomAccessFile | m_dataFile
Physical file containing serialized objects |
protected String | m_fileName
Name of the underlying physical file |
protected RecordFilter | m_filter
Filter to be applied to each object read or written |
protected long | m_firstDeleted
File position of the first delete record |
Constructor Summary | |
---|---|
ObjectDatabaseFile(String name, boolean is_new)
Creates or opens a file that stores objects in variable-length records.
| |
ObjectDatabaseFile(File file, boolean is_new)
Creates or opens a file that stores objects in variable-length records.
|
Method Summary | |
---|---|
void | assignFilter(RecordFilter filter)
Assigns a filter object to translated, encrypt, compress, or otherwise manipulate
objects as they are written and read.
|
void | close() |
void | compact(ObjectDatabaseCallback callback)
Compacts a database file by copying it to a new file and deleting the old one.
|
protected ObjectInputStream | createObjectInputStream(InputStream in) |
protected ObjectOutputStream | createObjectOutputStream(OutputStream out) |
void | delete()
Deletes the record in the current file position.
|
FileDescriptor | getFD() |
long | getFilePointer() |
long | length() |
Object | readObject() |
void | rewind()
Sets the current file pointer to the first byte beyond the file header.
|
void | rewriteObject(Serializable obj)
Re-writes a serializable object to the file, at the current file position.
|
void | seek(long pos) |
void | skip()
Skips the record at the current file position, moving to the next record in sequence.
|
long | writeObject(Serializable obj)
Writes a serializable object to the file. |
Parameters: name name of the file to be created is_new true
when a new file should be created, overwriting
any existing file with the same name; false
when
opening and using an existing file
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
Parameters: file indentity of the file to be created is_new true
when a new file should be created, overwriting
any existing file with the same identity; false
when
opening and using an existing file
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
Parameters: filter assigned filter
Parameters: callback called for each record rewritten to the compacted file
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class ClassNotFoundException for a casting error, usually when a persistent object or index does match the expected type
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
Parameters: obj serializable object to be written as a record
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class
writeObject
stores the
new record in the first "deleted" location of sufficient size, or
it appends the new record if suitable deleted space is not available.
Parameters: obj serializable object to be written as a record
Returns: file position of the newly-written record
Throws: IOException when an I/O exception is thrown by an underlying java.io.* class