/* DBReader.java (P)1999-2002 Laurentiu Cristofor */ /* laur.dm.ar - A Java package for association rule mining Copyright (C) 2002 Laurentiu Cristofor This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA The laur.dm.ar package was written by Laurentiu Cristofor (laur@cs.umb.edu). */ package laur.dm.ar; import java.io.*; import java.util.ArrayList; /** A DBReader is used to read data from a database. @version 1.0 @author Laurentiu Cristofor */ /* Database header specification: 1. Identifier - 3 characters - CKL 2. Database format version number - 3 integers - 1 12 3 (meaning 1.12.3) 3. Header size - 1 long - the size of the header in bytes, lets us know where the data starts 4. Number of rows - 1 long 5. Number of columns - 1 long 6. Column names - fixed length fields (32 characters). There are as many such entries as we have columns in the database. 7. Identifier - 3 characters - CKL : for verification only, it indicates the end of the column names enumeration. 8. Database description - fixed length field (256 characters). 9. Identifier - 3 characters - CKL : again for verifying the end of the description 10. CRC field - 1 int - CRC of the data part of the file only Database contents: each row consists of ints: no_items, item 1, ... item n */ public class DBReader { private static final int COLUMN_LENGTH = DBWriter.COLUMN_LENGTH; private static final int DESCRIPTION_LENGTH = DBWriter.DESCRIPTION_LENGTH; private static final String ID = DBWriter.ID; private RandomAccessFile inStream; private String version; private String description; private ArrayList names; private long numRows; private long numColumns; private int CRC; private long headerSize; private boolean needReposition; private long lastPosition; private long currRow; // call this method to check the existence of the ID; // the file pointer must be already positioned private void checkID() throws IOException { for (int i = 0; i < ID.length(); i++) if (inStream.readChar() != ID.charAt(i)) throw new IOException("Attempting to load invalid database"); } /** * Create a new DBReader according to the input file name. * * @param fileName the name of the file * @exception IOException from library call */ public DBReader(String fileName) throws IOException { inStream = new RandomAccessFile(fileName, "r"); checkID(); version = ""; version += inStream.readInt() + "." + inStream.readInt() + "." + inStream.readInt(); headerSize = inStream.readLong(); numRows = inStream.readLong(); numColumns = inStream.readLong(); names = new ArrayList((int)numColumns); for (int i = 0; i < numColumns; i++) { String aString = ""; for (int j = 0; j < COLUMN_LENGTH; j++) aString += inStream.readChar(); aString = aString.trim(); names.add(aString); } checkID(); description = ""; for (int i = 0; i < DESCRIPTION_LENGTH; i++) description += inStream.readChar(); description = description.trim(); checkID(); CRC = inStream.readInt(); currRow = 1; needReposition = false; } /** * Close the I/O stream. */ public void close() throws IOException { inStream.close(); } /** * Get the file version number. * * @return a String containing the version (ex: 1.1.7) */ public String getVersion() { return version; } /** * Get the number of the rows in database. * * @return number of rows in database */ public long getNumRows() { return numRows; } /** * Get the number of the columns in database. * * @return number of columns in database */ public long getNumColumns() { return numColumns; } /** * Get all the column names for database. * * @return a ArrayList containing the column names */ public ArrayList getColumnNames() { return names; } /** * Get the i-th column name from database. * * @param i the index of the column requested * @return name of column */ public String getColumnName(int i) throws DBException { if (i < 0 || i >= numColumns) throw new DBException("Invalid column index"); return (String)names.get(i); } /** * Get the description of the database. */ public String getDescription() { return description; } /** * Check the integrity of the database. * * @exception IOException from library call * @return true if test passed, false otherwise */ public boolean checkIntegrity() throws IOException { int crc = 0; if (needReposition == false) { lastPosition = inStream.getFilePointer(); needReposition = true; } inStream.seek(headerSize); for (int i = 0; i < numRows; i++) { int numItems = inStream.readInt(); crc = DBWriter.updateCRC(crc, numItems); for (int j = 0; j < numItems; j++) crc = DBWriter.updateCRC(crc, inStream.readInt()); } if (crc == CRC) return true; else return false; } /** * Get first row of the table from the data file. * * @exception IOException from library call * @exception DBException an invalid item has been met * @return first Itemset from database */ public Itemset getFirstRow() throws IOException, DBException { currRow = 1; inStream.seek(headerSize); needReposition = false; return getNextRow(); } /** * Get the next row of data since last reading. * * @exception IOException from library call * @exception DBException an invalid item has been met */ public Itemset getNextRow() throws IOException, DBException { if (currRow > numRows) throw new IOException("EOF reached"); if (needReposition == true) { inStream.seek(lastPosition); needReposition = false; } int numItems = inStream.readInt(); int item; Itemset is = new Itemset(numItems); for (int i = 0; i < numItems; i++) { item = inStream.readInt(); if (item > numColumns) throw new DBException("Read an invalid item"); is.add(item); } currRow++; return is; } /** * Tell whether there are more rows to be read from the database. * * @return true if there are more rows, false otherwise */ public boolean hasMoreRows() { return (currRow } /** * sample usage and testing */ public static void main(String arg[]) { System.out.println("\n\nTrying to open nonexistent database:"); try { DBReader dbr = new DBReader("nonexistent.db"); } catch (Exception e) { System.out.println(e); } System.out.println("\n\nTrying to open invalid database:"); try { DBReader dbr = new DBReader("invalid.db"); } catch (Exception e) { System.out.println(e); } System.out.println("\n\nTrying to open corrupted database:"); try { DBReader dbr = new DBReader("corrupted.db"); System.out.println("No rows: " + dbr.getNumRows()); System.out.println("No columns: " + dbr.getNumColumns()); System.out.println("Third column name is: " + dbr.getColumnName(2)); System.out.println("Description: " + dbr.getDescription()); System.out.println("Version: " + dbr.getVersion()); System.out.println("Integrity check result: " + dbr.checkIntegrity()); while (dbr.hasMoreRows()) System.out.println(dbr.getNextRow()); } catch (Exception e) { System.out.println(e); } System.out.println("\n\nTrying to open empty database:"); try { DBReader dbr = new DBReader("empty.db"); System.out.println("No rows: " + dbr.getNumRows()); System.out.println("No columns: " + dbr.getNumColumns()); System.out.println("Third column name is: " + dbr.getColumnName(2)); System.out.println("Description: " + dbr.getDescription()); System.out.println("Version: " + dbr.getVersion()); System.out.println("Integrity check result: " + dbr.checkIntegrity()); while (dbr.hasMoreRows()) System.out.println(dbr.getNextRow()); } catch (Exception e) { System.out.println("Shouldn't have happened: " + e); } System.out.println("\n\nTrying to open correct database:"); try { DBReader dbr = new DBReader("correct.db"); System.out.println("No rows: " + dbr.getNumRows()); System.out.println("No columns: " + dbr.getNumColumns()); System.out.println("Third column name is: " + dbr.getColumnName(2)); System.out.println("Description: " + dbr.getDescription()); System.out.println("Version: " + dbr.getVersion()); System.out.println("Integrity check result: " + dbr.checkIntegrity()); while (dbr.hasMoreRows()) System.out.println(dbr.getNextRow()); } catch (Exception e) { System.out.println("Shouldn't have happened: " + e); } } }
