Java replace specific string in text file

Question

I've got a text file called log.txt. It's got the following data

1,,Mon May 05 00:05:45 WST 2014,textFiles/a.txt,images/download.jpg
2,,Mon May 05 00:05:45 WST 2014,textFiles/a.txt,images/download.jpg

The numbers before the first comma are indexes that specify each item.

What I want to do is to read the file and then replace one part of the string(e.g. textFiles/a.txt) in a given line with another value(e.g. something/bob.txt).

This is what I have so far:

    File log= new File("log.txt");
                    String search = "1,,Mon May 05 00:05:45 WST 2014,textFiles/a.txt,images/download.jpg;
                    //file reading
                    FileReader fr = new FileReader(log);
                    String s;
                    try (BufferedReader br = new BufferedReader(fr)) {
                        
                        while ((s = br.readLine()) != null) {
                            if (s.equals(search)) {
                                //not sure what to do here
                            }
                        }
                    }

Answer 1

One approach would be to use String.replaceAll():

File log= new File("log.txt");
String search = "textFiles/a\\.txt";  // <- changed to work with String.replaceAll()
String replacement = "something/bob.txt";
//file reading
FileReader fr = new FileReader(log);
String s;
try {
    BufferedReader br = new BufferedReader(fr);

    while ((s = br.readLine()) != null) {
        s.replaceAll(search, replacement);
        // do something with the resulting line
    }
}

You could also use regular expressions, or String.indexOf() to find where in a line your search string appears.

Answer 2

You could create a string of total file content and replace all the occurrence in the string and write to that file again.

You could something like this:

File log= new File("log.txt");
String search = "textFiles/a.txt";
String replace = "replaceText/b.txt";

try{
    FileReader fr = new FileReader(log);
    String s;
    String totalStr = "";
    try (BufferedReader br = new BufferedReader(fr)) {

        while ((s = br.readLine()) != null) {
            totalStr += s;
        }
        totalStr = totalStr.replaceAll(search, replace);
        FileWriter fw = new FileWriter(log);
    fw.write(totalStr);
    fw.close();
    }
}catch(Exception e){
    e.printStackTrace();
}

Answer 3

Solution with Java Files and Stream

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

private static void replaceAll(String filePath, String text, String replacement) {
        
        Path path = Paths.get(filePath);
        // Get all the lines
        try (Stream<String> stream = Files.lines(path, StandardCharsets.UTF_8)) {
            // Do the replace operation
            List<String> list = stream.map(line -> line.replace(text, replacement)).collect(Collectors.toList());
            // Write the content back
            Files.write(path, list, StandardCharsets.UTF_8);
        } catch (IOException e) {
            LOG.error("IOException for : " + filePath, e);
            e.printStackTrace();
        }
    }

Usage

replaceAll("test.txt", "original text", "new text");

Answer 4

A very simple solution would be to use:

s = s.replace( "textFiles/a.txt", "something/bob.txt" );

To replace all occurrences, use replaceAll shown in another proposal, where a regular expression is used - take care to escape all magic characters, as indicated there.