how to delete the content of text file without deleting itself

Question

I want to copy the content of file 'A' to file 'B'. after the copying is done I want to clear the content of file 'A' and want to write on it from its beginning. I can't delete file 'A' as it is related to some other task.

I was able to copy the content using java's file API(readLine() ), but don't know how to clear the content of file and set the file pointer to the beginning of the file.

score 152 · Accepted Answer · answered Aug 09 '11 at 10:20

152

Just print an empty string into the file:

PrintWriter writer = new PrintWriter(file);
writer.print("");
writer.close();

answered Aug 09 '11 at 10:20

Vlad

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The write isn't necessary, and if another task has the file open the open may not even be possible. – user207421 Dec 15 '13 at 07:13
writer.close??, we are in 2017!!!. Also, no need to print(""), because the text will be overwritten – FSm Feb 16 '17 at 20:11
3

@Andro, notice the timestamp and tags? Back then I remember it was the most reliable way to empty a file across Android devices. – Vlad Feb 17 '17 at 20:17
@Vlad If there is no need to close writer now, maybe this is a good idea to update answer? – Line Nov 03 '17 at 13:17
@Vlad This has never been the most reliable way, and the write is still unnecessary. It isn't reliable at all because of the swallowed exceptions, and reliable alternatives have existed since at leat 1996. – user207421 Sep 13 '21 at 08:28
@user207421, like I said, at that point I came across a number of Android devices and implementations that were not fully compliant with the Java SDK. Error/exception handling was never discussed and was left to the user of the snippet. – Vlad Sep 13 '21 at 08:35
As my experience with Android nowadays is nearly zero, I'd prefer to not edit the answer but rather let other/better answers bubble up to the top. Thank you all! – Vlad Sep 13 '21 at 08:36

score 86 · Answer 2 · edited Mar 25 '19 at 14:05

86

I don't believe you even have to write an empty string to the file.

PrintWriter pw = new PrintWriter("filepath.txt");
pw.close();

edited Mar 25 '19 at 14:05

Roshana Pitigala

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answered Dec 15 '13 at 05:27

camleng

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You are correct about that. All the answers showing a write are wrong or at best redundant. – user207421 Dec 15 '13 at 07:13
39

How about just `new PrintWriter("filepath.txt").close();`? – Ky - Dec 12 '14 at 03:30
1

quote from java docs "If the file exists then it will be truncated to zero size" – Lv99Zubat Jun 20 '16 at 15:00
1

but what to do if the file is in append mode. – GURMEET SINGH Oct 25 '17 at 23:11
Oh man I cant believe I missed the simple answer. Open file in truncate mode. I hate truncate mode so much that it slipped me. – Aug 26 '19 at 15:14

score 31 · Answer 3 · answered Aug 09 '11 at 10:20

31

You want the setLength() method in the class RandomAccessFile.

answered Aug 09 '11 at 10:20

Burleigh Bear

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This is in fact the only correct answer, as it doesn't delete the file. All other answers do. – user207421 Dec 15 '13 at 07:14
1

I need this because I would like to clear the log file created by [logback-android](https://github.com/tony19/logback-android) library. If I delete the log file manually, the library is not clever enough the create it again if there is log to write until I relaunch my app. Therefore, I used this method and work. I haven't study much. Is't it the best approach? Please advice. – Yeung Dec 16 '13 at 09:14
funnily, I have a production issue because Intenso card class 10 freeze (and force battery reset) when I call fileOnSdCard.setLength(0) for an app installed from .apk file. Their class 4 card never showed the issue. – Poutrathor Feb 22 '16 at 11:22

score 19 · Answer 4 · edited May 21 '16 at 13:42

19

Simple, write nothing!

FileOutputStream writer = new FileOutputStream("file.txt");
writer.write(("").getBytes());
writer.close();

edited May 21 '16 at 13:42

getsadzeg

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answered Aug 09 '11 at 10:11

Micky

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-1: java.lang.String does not have a toByteArray() method, neither in 6 nor 7. http://docs.oracle.com/javase/6/docs/api/java/lang/String. – james.garriss May 16 '12 at 19:32
1

It exists for a long time : http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#getBytes() – kmas Sep 03 '13 at 15:13
1

The write is unnecessary here. – user207421 Dec 15 '13 at 07:11
@kmas Your link is to `String.getBytes()`, which is not the same thing as `String.toByteArray()` as was originally coded here. – user207421 Sep 13 '21 at 08:29
The write here does exactly nothing. It is redundant. – user207421 Sep 13 '21 at 08:30

score 13 · Answer 5 · edited Jul 06 '18 at 17:05

13

One liner to make truncate operation:

FileChannel.open(Paths.get("/home/user/file/to/truncate"), StandardOpenOption.WRITE).truncate(0).close();

More information available at Java Documentation: https://docs.oracle.com/javase/7/docs/api/java/nio/channels/FileChannel.html

edited Jul 06 '18 at 17:05

Kröw

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answered Apr 12 '16 at 08:04

Michał

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+1 For not instantiating an entire file writing class, (and even worse writing to it). This should really be the accepted answer. – Kröw Jul 06 '18 at 15:54

score 6 · Answer 6 · answered Sep 20 '14 at 18:10

One of the best companion for java is Apache Projects and please do refer to it. For file related operation you can refer to the Commons IO project.

The Below one line code will help us to make the file empty.

FileUtils.write(new File("/your/file/path"), "")

score 6 · Answer 7 · edited Jan 15 '15 at 10:49

6

How about below:

File temp = new File("<your file name>");
if (temp.exists()) {
    RandomAccessFile raf = new RandomAccessFile(temp, "rw");
    raf.setLength(0);
}

edited Jan 15 '15 at 10:49

Tom

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answered Jan 15 '15 at 10:07

Sanjay Singh

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score 5 · Answer 8 · answered Aug 09 '11 at 10:17

5

After copying from A to B open file A again to write mode and then write empty string in it

answered Aug 09 '11 at 10:17

Rasel

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Manh Vu · Answer 9 · 2013-06-22T05:24:10.147

4

Just write:

FileOutputStream writer = new FileOutputStream("file.txt");

edited Jun 22 '13 at 05:24

answered Jun 20 '13 at 14:09

Manh Vu

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score 2 · Answer 10 · answered Mar 13 '17 at 03:48

2

If you don't need to use the writer afterwards the shortest and cleanest way to do it would be like that:

new FileWriter("/path/to/your/file.txt").close();

answered Mar 13 '17 at 03:48

MarkoPaulo

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score 2 · Answer 11 · answered Aug 09 '11 at 10:11

2

Write an empty string to the file, flush, and close. Make sure that the file writer is not in append-mode. I think that should do the trick.

answered Aug 09 '11 at 10:11

hakon

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Just opening and closing it in non-append mode will do that. The write does literally nothing. – user207421 Sep 13 '21 at 08:31

score 0 · Answer 12 · answered Aug 26 '18 at 09:33

using : New Java 7 NIO library, try

        if(!Files.exists(filePath.getParent())) {
            Files.createDirectory(filePath.getParent());
        }
        if(!Files.exists(filePath)) {
            Files.createFile(filePath);
        }
        // Empty the file content
        writer = Files.newBufferedWriter(filePath);
        writer.write("");
        writer.flush();

The above code checks if Directoty exist if not creates the directory, checks if file exists is yes it writes empty string and flushes the buffer, in the end yo get the writer pointing to empty file

Everything after `Empty the file content` is redundant. And you forgot the close. — user207421, Sep 13 '21 at 08:32

score 0 · Answer 13 · answered Aug 26 '19 at 15:16

0

All you have to do is open file in truncate mode. Any Java file out class will automatically do that for you.

answered Aug 26 '19 at 15:16

score -1 · Answer 14 · answered Nov 23 '14 at 01:45

You can use

FileWriter fw = new FileWriter(/*your file path*/);
PrintWriter pw = new PrintWriter(fw);
pw.write("");
pw.flush(); 
pw.close();

Remember not to use

FileWriter fw = new FileWriter(/*your file path*/,true);

True in the filewriter constructor will enable append.

score -1 · Answer 15 · edited Nov 18 '17 at 18:30

-1

FileOutputStream fos = openFileOutput("/*file name like --> one.txt*/", MODE_PRIVATE);
FileWriter fw = new FileWriter(fos.getFD());
fw.write("");

edited Nov 18 '17 at 18:30

Saca

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answered Mar 22 '17 at 19:16

Harpreet Singh

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Welcome to SO! Please use the built-in formatting tools to make your code easier to read. – Michael L. Mar 22 '17 at 19:37
What is `openFileOutput()`? You don't need all this, and you've concealed the only interesting part. – user207421 Sep 13 '21 at 08:33

score -1 · Answer 16 · answered May 16 '18 at 14:55

With try-with-resources writer will be automatically closed:

import org.apache.commons.lang3.StringUtils;
final File file = new File("SomeFile");
try (PrintWriter writer = new PrintWriter(file))  {
    writer.print(StringUtils.EMPTY);                
}
// here we can be sure that writer will be closed automatically

score -2 · Answer 17 · edited Nov 24 '14 at 14:10

-2

you can write a generic method as (its too late but below code will help you/others)

public static FileInputStream getFile(File fileImport) throws IOException {
      FileInputStream fileStream = null;
    try {
        PrintWriter writer = new PrintWriter(fileImport);
        writer.print(StringUtils.EMPTY);
        fileStream = new FileInputStream(fileImport);
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            writer.close();
        }
         return fileStream;
}

edited Nov 24 '14 at 14:10

techGaurdian

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answered Apr 07 '13 at 18:39

Vishal

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This does not create an empty file, it creates a file with one null byte in it. – user207421 Dec 15 '13 at 07:12

how to delete the content of text file without deleting itself

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