How to replace string in a file

[David Sundo]

I need help! basically I have a file called "test.txt" The content of the file is as followed:
---------------Test.txt---------
Honda Civic, 4LSXL,red = 2000
Honda Accord, 3HUV, blue = 1999
Nissan Maxima, 5JKLU, green =2001
Acura Integra, JK22L, red = 2003
----------------------------------
Basically I want to replace "Nissan Maxima, 5JKLU, Green=2001" with "Nissan Altima, 6LRTU, Yellow=1999". Can any one tell me what is the easiest way to do this?
I already started to read the file, I need some help!
Thanks,
David Sundo
------------Code----------------------------
StringBuffer data = new StringBuffer();

LineNumberReader in = new LineNumberReader(new FileReader("test.txt"));
while ((line = in.readLine()) != null){
data.append(line);
data.append("\n");
}

[Stan James]

I'll guess you want a Swing UI, and we'll work against the text file kinda like it was a single-user database. See if this sings to you:

main driver:
   read the file
   edit car records
   rewrite the file
read the file:
   open the file
   while not eof
      read a line
      create a car object 
   close the file
edit car records:
   show a car
   let user select next, prior
   let user add a new empty car
   let user delete a car
   let user type in car data
rewrite the file:
   open file in replace mode
   for each car object
      write a line describing the car
   close the file

Doea that makes sense? Does it hint at some unit tests you can write? Responsibilities for different classes? This is a classic "functional decomposition" analysis, not very OO ... yet.
[ July 21, 2003: Message edited by: Stan James ]

[Bear Bibeault]

I'll guess you want a Swing UI,

??? I have no idea where Swing or a GUI comes into this...

Basically I want to replace...

Some ideas: you may want to look into regular expressions to locate the text you want to replace (I'm assuming you aren't going to hard-code the string into the program). If you aren't going to do any pattern matching, regular expressions may be over-kill, and you may just need the String.indexOf() method.
Then there are methods in the String class that will help you extract the sub-strings necessary to rebuild a new string using your string buffer.
hth,
bear

[Stan James]

Yeah, that Swing bit was a leap. If this is the least work you can do to update a file you can start by deciding if you want the whole file in memory or not.

while not eof
   read a line
   if this is the line we want to change
      write the new stuff
   else
      write the original line
end while
//
// Opposed to
//
   read the whole file into one giant string
   replace old with new - candidate for regexp 
   rewrite the whole file

I used to work on an OS called CMS that had a safe file replacement strategy, used in COPY and certain other output that replaced an existing file:

write new stuff to Temp1
rename Original to Temp2
rename Temp1 to Original
erase Temp2

This gives a "least bad" result if anything croaks in mid flight.
Yet another approach: You CAN update the file in place. Force all car records to have the same number of bytes. Use RandomAccessFile to seek a position (record number * record length) and read (record length) bytes. If you find the old data, seek the same position again, and write the new bytes. Just for practice with test first coding, I made a random access fixed length file class with the following public methods:

new RandomFile( FileName, RecordLength )
open( mode )
read( RecordNumber )
append( Record )
rewrite( RecordNumber, Record )
getRecordCount()
close()

If that sounds like fun, I'd be happy to share it. Or maybe just the Junit test first.

[Dirk Schreckmann]

Stan, I'd enjoy a look at what you did. And if you are in the mood to give us the blow-by-blow through the unit tests and the implementation, well that'd just be... awesome!

[Stan James]

I moved this to the IO forum here. So far I just posted the unit tests. Implementation tomorrow?

[Dirk Schreckmann]

Cool.

[Jaunty John]

Try this...
//~ Formatted by jFormat�2003 EMail: [email protected] 2003.07.23
import java.io.*;
import java.util.*;
public class ReadReplaceText {
public static void main(String args[]) throws IOException {
ArrayList inFile = new ArrayList();
ArrayList outFile = new ArrayList();
int iJ=0;
String oldStr = "Nissan Maxima, 5JKLU, Green =2001";//Old_String
String newStr = "Nissan Altima, 6LRTU, Yellow=1999";//New string
try {
FileReader fr = new FileReader("test.txt");// Create a char stream reader
BufferedReader br = new BufferedReader(fr);//A line reader
String str;
while((str = br.readLine()) != null) {
inFile.add(str);//~inFile is an AryFile TYPE
//System.out.println(str);
}
fr.close();
//And now manipulate the file...
for(int iK=0; iK<inFile.size(); iK++) {
str = (String) inFile.get(iK);
System.out.println(str);
iJ = str.indexOf(oldStr);
//iJ will equal 0 when current string matches Old_String
if(iJ == 0) {
outFile.add(iK, newStr);
//System.out.println(">>> " + str);
}
else {
outFile.add(iK, str);
}
}//~for(int iK=0; iK<inFile....
System.out.println();
//Write the File
PrintWriter pw = new PrintWriter(new FileWriter("test.txt"));
for(int iK=0; iK<inFile.size(); iK++) {
str = (String)outFile.get(iK);
pw.println(str);
System.out.println(str);
}
pw.close();
}//~try...
catch (IOException ex) {
ex.printStackTrace();
}
}//~public static void main(...
}//~public class ReadReplace...