Delete Line with BufferedReader

Question

I am currently reading a .txt file from my computer using this code:

BufferedReader in = new BufferedReader(new FileReader("./Data/text.txt"));
String data = null;
try {
    while ((data = in.readLine()) != null) {
        String[] args = data.split(":");

        if (args[1] == "yes")) {
            file.add(data);
        } else {
            //Remove line here  
        }
    }
} finally {
    in.close();
}

Now for every line I read I do a simple if check, if the answer is not "yes" I want to delete the line and continue to the next one.

Is this possible? Or can you only read and not change?

You are using a `Reader` class, so you can't do it. – Dhrubajyoti Gogoi May 09 '14 at 12:05 — Dhrubajyoti Gogoi, May 09 '14 at 12:05

score 4 · Answer 1 · answered May 09 '14 at 12:00

4

You can not "delete" a specific line from a file, but you can read the lines, remove the unwanted and overwrite the file content with the cleaned lines.

answered May 09 '14 at 12:00

Smutje

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giannis christofakis · Answer 2 · 2014-05-15T09:51:15.463

As already been said you can read all the lines and skip the ones don't want, after that you can store the rest of them in the same file.

    List<String> file = new ArrayList();

    BufferedReader in = new BufferedReader(new FileReader("./Data/text.txt"));
    String data = null;
    try {
        while ((data = in.readLine()) != null) {
            String[] args = data.split(":");

            if (args[1].equals("yes")) {
                file.add(data);
            } else {
                //skip this line
            }
        }
        in.close();

        //Add to file
        FileWriter fw = new FileWriter("./Data/text.txt");
        BufferedWriter out = new BufferedWriter(fw);
        for (String line : file) {
            out.write(line + "\n");
        }
        out.flush();
        out.close();

    } catch (Exception e){

    }

You can also use Apache Commons IO.

    File file = new File("./Data/text.txt");
    List<String> lines = org.apache.commons.io.FileUtils.readLines(file)

    for (int i = 0; i < lines.size(); i++) 
        if (! lines.get(i).split(":")[1].equals("yes")) 
            lines.remove(i--);

    org.apache.commons.io.FileUtils.writeLines(file, lines);

You must be very careful with arg[1] if you have an empty line the result would be an ArrayIndexOutOfBoundsException.

Addendum

I'd like to post another way using Java 8 lambda expressions and Java 7 java.nio.file.* package.

    List<String> lines = Files.readAllLines(Paths.get("./Data/text.txt"), Charset.defaultCharset());

    Predicate<String> filter = line -> line.split(":")[1].equals("./Data/text.txt");

    String output = lines
            .stream()
            .filter(filter)
            .map(l -> l + "\n")
            .collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)
            .toString();

    Files.write(Paths.get("test"), output.getBytes());

You might want to add back in the newlines, between lines. ;) — Peter Lawrey, May 09 '14 at 12:27

Peter Lawrey · Answer 3 · 2014-05-09T15:19:10.863

0

The simplest solution is to copy all the lines you want to keep and replace the existing file with the one you just created.

File orig = new File("Data/text.txt");
File tmp = new File(orig+".tmp");
try (BufferedReader in = new BufferedReader(new FileReader(orig));
     PrintWriter pw = new PrintWriter(new FileWriter(tmp))) {
     for (String data; (data = in.readLine()) != null; )
          if (data.split(":")[1].equals("yes"))
              pw.println(data);
}
if (orig.delete())
    tmp.renameTo(orig);
else
    // cannot delete old file :|

edited May 09 '14 at 15:19

answered May 09 '14 at 12:27

Peter Lawrey

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@gia nnischristofakis Good point. Changed it to match the question assuming there is exactly one `:` – Peter Lawrey May 09 '14 at 13:05
Sorry but I think it's still wrong. Assume the line is `adfas:yes:asdfas`. – giannis christofakis May 09 '14 at 13:06
@giannischristofakis I did say, assuming there is exactly one `:` – Peter Lawrey May 09 '14 at 13:12
1

Sorry my bad, I think it's `renameTo`. – giannis christofakis May 09 '14 at 13:53

score 0 · Answer 4 · answered May 09 '14 at 12:29

Correct me if I'm wrong, but that code of yours already 'delete' unwanted line (args[1] != "yes"), why? Because that IF of yours has a statement like:

IF 'args[1]' is 'yes' THEN add it to 'file' ELSE do nothing

That says, other than yes then it won't be added to file, you should you check file's content (I assume it's a List<String> type), but I'm pretty sure that your code is already correct as it is.

Or you can add continue; in that else block.

Delete Line with BufferedReader

4 Answers4