ObjectDatabaseFile

java.lang.Object
- 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

Fields
Modifier and Type	Field and Description
`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

Constructors
Constructor and Description
`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

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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

Class ObjectDatabaseFile

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

DEL_LIST_END

IS_DELETED

IS_ACTIVE

m_dataFile

m_fileName

m_firstDeleted

m_filter

Constructor Detail

ObjectDatabaseFile

ObjectDatabaseFile

Method Detail

writeObject

rewriteObject

readObject

delete

rewind

skip

compact

assignFilter

getFD

getFilePointer

seek

length

close

createObjectInputStream

createObjectOutputStream