Text compare

This is not flex related, I know but since I don't have another blog to post this in, I will put it in this one:) so bare with me. Following my last post which was about implementing track changes in flex side, I decided to get a text comparison algorithm on the server java side to compare two texts and return a merged version with all additions and deletions.

I found a number of character/line comparison algos but the output wasn't that nice and i decided to look for a word by word comparison for change tracking. What I found was a "longest common subsequences algorithm" for Java but it was based on two linked lists or arrays. So decided to complement this with a textutil compare method that receives as a parameters two version of the text and produces a merged copy with deletions wrapped in "[-" & "-]" and additions wrapped in "[+" & "+]".

/** * Breaks ups a string of text of a series of words * @param text * @return list of words */ public static List extractWords (String text) { BreakIterator bi = BreakIterator.getWordInstance(); List words = new ArrayList(); bi.setText(text); int index =0; while (bi.next() != BreakIterator.DONE) { words.add(text.substring(index,bi.current())); System.out.print(/*(words.size()-1) +*/ text.substring(index,bi.current())); index = bi.current(); } System.out.println(); System.out.println(); return words; } /** * Compares and finds changes require to be done on text 1 to change it to text 2 * @param text1 * @param text2 * @return a copy of text1 with all merged changes of text2 * deletions are wrapped in "[-" "-]" additions are wrapped in "[+" and "+]" * */ public static String compareText( String text1, String text2) { List list= extractWords(text1); List list2= extractWords(text2); Diff diff = new Diff (list,list2); List diffList = diff.diff(); Iterator itr = diffList.iterator(); Difference difference; String mergedText= ""; int i=0; int delStart=-1; int addStart=-1; int delEnd=-1; int addEnd=-1; while (itr.hasNext()) //iterate through the difference list. { difference = itr.next(); delStart = difference.getDeletedStart(); delEnd = difference.getDeletedEnd(); addStart = difference.getAddedStart(); addEnd = difference.getAddedEnd(); while ( i < delStart ) { //copy all text before the current delete from the old text mergedText += list.get(i); i++; } if (delEnd != Difference.NONE) { //elseif DelEnd == None => nothing was deleted, most probably only addition mergedText += "[-"; while (i<= delEnd)//wrap the delete { mergedText += list.get(i); i++; } mergedText += "-]" ; } if (addEnd != Difference.NONE) { //elseif Addend == None => nothing was added, most probably only delete mergedText += "[+"; for (int j=addStart; j <= addEnd; j++) { mergedText += list2.get(j); } mergedText += "+]" ; } } while (i <>//copy the reset of the unchanged text. { mergedText += list.get(i); i++; } return mergedText; }