Processing line by line text in a file using java io

Question

hi,
i am able to do the basic file handling such reading files, creating a new text file, appending data etc..etc... using java.
But now i am having a text file containing many lines of sql update statements. i need to go through each line, execute the line in database and if it is successfull then the corresponding line will be deleted. In process of going through these many lines if the connection with database ends abruptly in between then i must be left with all the lines that were not updated in the database.
Thus if there is no failure in the connection during the process then all lines will be executed and the file will be emptied. on the other hand if connection ends in between then all the lines which were not executed will be left in the file.
i think the above process could be summarized[b] as to go through the each line in a text file..do some processing and delete the correspondng line and then proceed to the next line and reapeat the above process until file end has been reached.
i didnt find any good methods to do such updations of file. so please help me...
thanx

Answer 1

If you really want to delete a line from a text file, you have to move everything after the line upwards. This is equivalent to deleting an item in an array - you have to shift everything after the item to keep it contiguous. However, I don't think that solution is what you want because it is very inefficient. It would be more efficient for you to read a line, perform the update, then move to the next line. If you get an error, or you come to the end of the file, you're finished. Once you're finished, start reading from the current position and write to the beginning of the file. At this point you would need to keep track of both positions. The easiest way is with a RandomAccessFile. Once you've moved all the remaining lines up in the file, just set the length of the file to the current position.