Find and replace string in file

Question

hi,
i need to find and replace text (string) data in about 100+ files, i've decided to write a small java program to do it but i'm stuck on how to replace.
here is what i'm heading towards:
class ReplaceString {
  BufferedReader in;
  BufferedReader os;
  public static void main(String args[]) {
    ReplaceString obj = new ReplaceString();
    obj.replace();
   void replace() {
     try {
       in = new BufferedReader(new FileReader("a.txt");
       os = new BufferdWriter(new FileWriter("a.txt");
       //  read until end of file
       String currentLine = new String();
       while((currenLine=is.readLine()) != null) {
         //  if matching text then replace????
         if(currentLine.equals("Version 001") {
            // how to now replace the Version 001 with Version 002???
     }catch(IOException e) {
        System.out.println(e);
        in.close();
        os.close();
     in.close();
     os.close();
}the above code i just typed so there might be errors, but looks ok to me, is there any way once i find the string i want to replace, to replace the string with another string. basically i want to replace all occurrences of the text "Version 001" with "Version 002"
Thank you.

Answer 1

Is it always true, as in your example, that the replacement is the same length as the existing string? If so, this one's easy.
Is it also true that you don't need to worry about 16-bit chars? (Again, as in your example.) If you're using just ASCII characters, this gets easier still.
1) Segregate the file I/O from the search/replace process.
2) Main becomes:
readFile();
replace( "this", "that" );
writeFile();Use a byte array buffer, defined in your main class. Fill it via the readFile() code. Use a RandomAccessFile, check its length() to allocate your byte array, then do a single read() to fill the buffer.
A brute force search will certainly work: scan for the first search character, then check the rest for a match, replace if you've got a match and continue scanning. Alternative if your file's aren't too big: create a String from the byte array:
// buffer is a byte array
String s = new String( buffer );And use the String.replaceAll() to do the search/replace. Recover the buffer with:
buffer = string.getBytes();A single write() and close() should handle the remaining work.