/**File Name : Database.java * *Authors : Prashanth. K * Shireen Javali * *Date : 20/05/2000 * *Function : Maintains a database of the search * strings and the corresponding url's */ /**The database consists of the following files: *The links file contains the list of links of the sites each *occupying 50 bytes of space *The index file contains a search string followed *by offsets in the links file where the strings are stored * *The data base is updated using 3 files *The links file , the index file & the temp file * *The temp file contains the new links to be entered */ import java.io.*; import java.util.StringTokenizer; import java.math.*; public class Database { /**This method updates the database by adding a search string to it *It takes care not to repeat a url while updating */ public void update(String indexFileName, String linksFileName,String tempFileName,String countFileName,String searchString) throws IOException { RandomAccessFile indexFile = new RandomAccessFile (indexFileName,"rw"); RandomAccessFile linksFile = new RandomAccessFile (linksFileName,"rw"); RandomAccessFile tempFile = new RandomAccessFile (tempFileName ,"rw"); RandomAccessFile countFile = new RandomAccessFile (countFileName,"rw"); RandomAccessFile tempIndexFile = new RandomAccessFile ("tempIndex.dat","rw"); String latest = new String(countFile.readLine()); int z = 0; byte spaces[]; spaces = new byte[200]; for (int i = 0 ; i < 200 ; i++) spaces[i] = (byte)' '; BigInteger latestIndex = new BigInteger(latest); BigInteger unity = new BigInteger("1"); int diff; long len = linksFile.length(); linksFile.seek(len); long lenOfTempFile = tempFile.length(); long fpOfTempFile = 0; long lenOfIndexFile = indexFile.length(); long indexFilePtr = 0; boolean notFound = true; indexFile.seek(0); String line; while(notFound && (indexFilePtr < lenOfIndexFile)) { line = indexFile.readLine(); if(line.trim().equals(searchString.trim())) notFound = false; else { tempIndexFile.writeBytes(line+"\r\n"); line = indexFile.readLine(); tempIndexFile.writeBytes(line+"\r\n"); } indexFilePtr = indexFile.getFilePointer(); } if(!notFound) { indexFile.readLine(); //write the remaining file while(indexFilePtr < lenOfIndexFile) { line = indexFile.readLine(); tempIndexFile.writeBytes(line+"\r\n"); indexFilePtr = indexFile.getFilePointer(); } } tempIndexFile.writeBytes(searchString+"\r\n"); byte buffer[] = new byte[200]; while(fpOfTempFile < lenOfTempFile) { try { System.out.println("here 3"); String link = new String(tempFile.readLine()); long fpOfLinksFile = 0; boolean found = false; linksFile.seek(0); long lenOfLinksFile = linksFile.length(); while (fpOfLinksFile < lenOfLinksFile) { linksFile.read(buffer); String str = new String (buffer); if (str.trim().equals(link.trim())) { found = true; break; } fpOfLinksFile = linksFile.getFilePointer(); } if (found) { fpOfLinksFile = linksFile.getFilePointer(); Long toBeWritten = new Long(fpOfLinksFile / 200); tempIndexFile.writeBytes(Long.toString(fpOfLinksFile / 200)+ " "); } else { System.out.println("here 4"); linksFile.writeBytes(link); System.out.println(link+" "+link.length()); diff = 200 - link.length(); System.out.println("here 5"); linksFile.write(spaces,0,diff); // linksFile.writeBytes("\r\n"); System.out.println("here 6"); latestIndex = latestIndex.add(unity); tempIndexFile.writeBytes(latestIndex.toString()+ " "); } System.out.println("here 7"); fpOfTempFile = tempFile.getFilePointer() ; System.out.println("here "+z++); } catch( NullPointerException e) { } } indexFile.writeBytes("\r\n"); countFile.seek(0); countFile.writeBytes(latestIndex.toString()); countFile.close(); linksFile.close(); indexFile.close(); tempFile.close(); tempIndexFile.close(); File iF = new File(indexFileName); File tiF = new File("tempIndex.dat"); iF.delete(); tiF.renameTo(iF); } public void deleteLinks(String token, String indexFileName,int idx[]) { //modify in case of no links try { RandomAccessFile indexFile = new RandomAccessFile (indexFileName,"rw"); RandomAccessFile tempIndexFile = new RandomAccessFile ("tempIndex.dat","rw"); int z = 0; int diff; long lenOfIndexFile = indexFile.length(); long indexFilePtr = 0; boolean notFound = true; indexFile.seek(0); String line; while(notFound && (indexFilePtr < lenOfIndexFile)) { line = indexFile.readLine(); if(line.trim().equals(token.trim())) notFound = false; else { tempIndexFile.writeBytes(line+"\r\n"); line = indexFile.readLine(); tempIndexFile.writeBytes(line+"\r\n"); } indexFilePtr = indexFile.getFilePointer(); } if(notFound) { indexFile.close(); tempIndexFile.close(); File iF = new File(indexFileName); File tiF = new File("tempIndex.dat"); iF.delete(); tiF.renameTo(iF); System.out.println("returning"); return; } //if found StringTokenizer storeIndex = new StringTokenizer(indexFile.readLine()," ",false); indexFilePtr = indexFile.getFilePointer(); //write the remaining file while(indexFilePtr < lenOfIndexFile) { line = indexFile.readLine(); tempIndexFile.writeBytes(line+"\r\n"); indexFilePtr = indexFile.getFilePointer(); } System.out.println("deleting links for "+token); tempIndexFile.writeBytes(token+"\r\n"); int idxPtr = 0; while(storeIndex.hasMoreTokens()) { if(idxPtr < idx.length) { if(idx[idxPtr] == idxPtr ) storeIndex.nextToken(); else tempIndexFile.writeBytes(storeIndex.nextToken()+ " "); } else tempIndexFile.writeBytes(storeIndex.nextToken()+ " "); idxPtr++; } tempIndexFile.writeBytes("\r\n"); indexFile.close(); tempIndexFile.close(); File iF = new File(indexFileName); File tiF = new File("tempIndex.dat"); iF.delete(); tiF.renameTo(iF); } catch(FileNotFoundException fe) { } catch(IOException ie) { } } /**This method searches if a string is present in database *and returns the corresponding url's */ public boolean search(String indexFileName,String linksFileName,String outFileName,String searchString) throws IOException { long fpOfIndexFile = 0; RandomAccessFile indexFile = null; RandomAccessFile linksFile = null; RandomAccessFile outFile = null; byte buffer[]; long lenOfIndexFile; try { indexFile = new RandomAccessFile (indexFileName,"rw"); linksFile = new RandomAccessFile (linksFileName,"rw"); outFile = new RandomAccessFile(outFileName,"rw"); buffer = new byte[200]; lenOfIndexFile = indexFile.length(); System.out.println("here 2"); while(fpOfIndexFile < lenOfIndexFile) { System.out.println("here 3"); if(indexFile.readLine().trim().equals(searchString.trim())) { System.out.println("file length "+outFile.length()); StringTokenizer t = new StringTokenizer(indexFile.readLine()," "); while(t.hasMoreTokens()) { BigInteger linkIndex = new BigInteger(t.nextToken()); long fp = linkIndex.longValue(); fp = (fp-1) *200; linksFile.seek(fp); linksFile.read(buffer); String str = new String (buffer); int i = str.indexOf(" "); str = str.substring(0,i); System.out.println(str); outFile.writeBytes(str+"\r\n"); } indexFile.close(); linksFile.close(); outFile.close(); return true; } else indexFile.readLine(); fpOfIndexFile = indexFile.getFilePointer(); }//while indexFile.close(); linksFile.close(); outFile.close(); return false; } catch(FileNotFoundException fe) { System.out.println(fe); return false; } catch(IOException ie) { System.out.println(ie); return false; } catch(NumberFormatException nfe) { System.out.println(nfe); return false; } catch(NullPointerException npe) { System.out.println(npe); fpOfIndexFile = indexFile.getFilePointer(); return false; } } }