com.coyotegulch.jisp
Class ObjectDatabaseFile

java.lang.Object
  extended by com.coyotegulch.jisp.ObjectDatabaseFile
Direct Known Subclasses:
IndexedObjectDatabase

public class ObjectDatabaseFile
extends java.lang.Object

The 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  java.io.RandomAccessFile m_dataFile
          Physical file containing serialized objects
protected  java.lang.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(java.io.File file, boolean is_new)
          Creates or opens a file that stores objects in variable-length records.
ObjectDatabaseFile(java.lang.String name, 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  java.io.ObjectInputStream createObjectInputStream(java.io.InputStream in)
           
protected  java.io.ObjectOutputStream createObjectOutputStream(java.io.OutputStream out)
           
 void delete()
          Deletes the record in the current file position.
 java.io.FileDescriptor getFD()
           
 long getFilePointer()
           
 long length()
           
 java.lang.Object readObject()
           
 void rewind()
          Sets the current file pointer to the first byte beyond the file header.
 void rewriteObject(java.io.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(java.io.Serializable obj)
          Writes a serializable object to the file.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DEL_LIST_END

protected static final long DEL_LIST_END
Marks the end of the list of deleted records

See Also:
Constant Field Values

IS_DELETED

protected static final byte IS_DELETED
Marks a given record as deleted

See Also:
Constant Field Values

IS_ACTIVE

protected static final byte IS_ACTIVE
Marks a given record as containing live data

See Also:
Constant Field Values

m_dataFile

protected java.io.RandomAccessFile m_dataFile
Physical file containing serialized objects


m_fileName

protected java.lang.String m_fileName
Name of the underlying physical file


m_firstDeleted

protected long m_firstDeleted
File position of the first delete record


m_filter

protected RecordFilter m_filter
Filter to be applied to each object read or written

Constructor Detail

ObjectDatabaseFile

public ObjectDatabaseFile(java.lang.String name,
                          boolean is_new)
                   throws java.io.IOException
Creates or opens a file that stores objects in variable-length records.

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:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

ObjectDatabaseFile

public ObjectDatabaseFile(java.io.File file,
                          boolean is_new)
                   throws java.io.IOException
Creates or opens a file that stores objects in variable-length records.

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:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
Method Detail

writeObject

public long writeObject(java.io.Serializable obj)
                 throws java.io.IOException
Writes a serializable object to the file. 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:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

rewriteObject

public void rewriteObject(java.io.Serializable obj)
                   throws java.io.IOException
Re-writes a serializable object to the file, at the current file position.

Parameters:
obj - serializable object to be written as a record
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

readObject

public java.lang.Object readObject()
                            throws java.io.IOException,
                                   java.lang.ClassNotFoundException
Throws:
java.io.IOException
java.lang.ClassNotFoundException

delete

public void delete()
            throws java.io.IOException
Deletes the record in the current file position.

Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

rewind

public void rewind()
            throws java.io.IOException
Sets the current file pointer to the first byte beyond the file header.

Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

skip

public void skip()
          throws java.io.IOException
Skips the record at the current file position, moving to the next record in sequence.

Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class

compact

public void compact(ObjectDatabaseCallback callback)
             throws java.io.IOException,
                    java.lang.ClassNotFoundException
Compacts a database file by copying it to a new file and deleting the old one. The records will be copied in sequence, and the callback function is called for each record as it is rewritten. The callback function is responsible for rebuilding any indexes or other referneces to the records, which will have new file positions after compaction.

Parameters:
callback - called for each record rewritten to the compacted file
Throws:
java.io.IOException - when an I/O exception is thrown by an underlying java.io.* class
java.lang.ClassNotFoundException - for a casting error, usually when a persistent object or index does match the expected type

assignFilter

public void assignFilter(RecordFilter filter)
Assigns a filter object to translated, encrypt, compress, or otherwise manipulate objects as they are written and read.

Parameters:
filter - assigned filter

getFD

public final java.io.FileDescriptor getFD()
                                   throws java.io.IOException
Throws:
java.io.IOException

getFilePointer

public long getFilePointer()
                    throws java.io.IOException
Throws:
java.io.IOException

seek

public void seek(long pos)
          throws java.io.IOException
Throws:
java.io.IOException

length

public long length()
            throws java.io.IOException
Throws:
java.io.IOException

close

public void close()
           throws java.io.IOException
Throws:
java.io.IOException

createObjectInputStream

protected java.io.ObjectInputStream createObjectInputStream(java.io.InputStream in)
                                                     throws java.io.IOException
Throws:
java.io.IOException

createObjectOutputStream

protected java.io.ObjectOutputStream createObjectOutputStream(java.io.OutputStream out)
                                                       throws java.io.IOException
Throws:
java.io.IOException