org.egothor.repository

Class DocumentsDB

java.lang.Object

org.egothor.repository.DocumentsDB

All Implemented Interfaces:

DataRepository

public class DocumentsDB
extends Object
implements DataRepository

DocumentsDB implements a documents DB structure on disc. The structure consists of two files: the first one is used as an index, and the second one as a data store. When you want to read the element with key uid the algorithm works as follows:

1. Read an offset of the element: firstfile.seek( uid*SIZEOFOFFSET ); offset = firstfile.read();
2. Read the element: secondfile.seek( offset ); object = secondfile.readTheObject();

Author:

Leo Galambos

Nested Class Summary

Nested classes/interfaces inherited from interface org.egothor.repository.DataRepository

DataRepository.TupleSequence

Constructor Summary

Constructors

Constructor and Description
DocumentsDB(String location, boolean compressed) Constructor for the DocumentsDB object.

Method Summary

Modifier and Type	Method and Description
int	addItem(long uid, byte[] document, int length) Adds another document into the repository.
void	close() Closes the structure.
void	destroy() Destroy this data structure.
DataInputStream	elementAt(long uid, int revision) Retrieves a data block.
DataRepository.TupleSequence	elements() The tuples are [long:uid;int:rev;Object:DataInputStream].
void	flush()
boolean	removeDoc(long uid) Removes an element of the given uid.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DocumentsDB

public DocumentsDB(String location,
                   boolean compressed)

Constructor for the DocumentsDB object. Open the structure in the given directory. Three files are created, all with the name doc , with varying extensions depending on the file's function: information about removed elements is stored in doc.btm , the first file of offsets in doc.idx , and the second file with elements data in doc.dta .

Parameters:

location - the location where the files will be created

compressed - true iff the DocumentData will be saved in gzip format

Method Detail

addItem

public int addItem(long uid,
                   byte[] document,
                   int length)

Description copied from interface: DataRepository

Adds another document into the repository. If the implementation is able to recognize whether the incoming data block is still the same (as the existing in the repository), it would discard the insertion request and return 0 as the signal of no-op.

Specified by:

addItem in interface DataRepository

Returns:

revision number (0 iff unchanged) or -1 when fails

elementAt

public DataInputStream elementAt(long uid,
                                 int revision)

Description copied from interface: DataRepository

Retrieves a data block.

Specified by:

elementAt in interface DataRepository

Parameters:

uid - the key of the block

revision - revision number of the block, 0 is used for the latest (current) revision

Returns:

null if the revision is not available (or the key is unknown)

destroy

public void destroy()

Destroy this data structure. First, it calls close(). Then it removes these files from the directory where the structure is stored: bitmap, idocs, docs.

Specified by:

destroy in interface DataRepository

removeDoc

public boolean removeDoc(long uid)

Removes an element of the given uid.

Parameters:

uid - the element to remove

Returns:

true if successful, false otherwise

close

public void close()

Closes the structure. It closes both data files (idocs and docs).

Specified by:

close in interface DataRepository

elements

public DataRepository.TupleSequence elements()

The tuples are [long:uid;int:rev;Object:DataInputStream].

Specified by:

elements in interface DataRepository

flush

public void flush()

Specified by:

flush in interface DataRepository