Filewriter will not append text to newly created file

Question

I'm fairly new to Java. I was trying to add "List:" to the beginning of a new text file if it doesn't exist. Instead, the text file is blank, with the input below a line of blank space.

File hi = new File("hi.txt");
try{
  if(!hi.exists()){
    System.out.printf("\nCreating 'hi.txt'."); 
    hi.createNewFile();
    String hello = "List:";
    new FileWriter(hi).append(hello);
  }
  else{
    System.out.printf("\nWriting to 'hi.txt'");
  }
  FileWriter writeHere = new FileWriter(hi, true);
  String uling = "hi";
  writeHere.append(uling);
  writeHere.close();
}
//error catching
catch(IOException e){
  System.out.printf("\nError. Check the file 'hi.txt'.");}

FileWriter needs a second argument to enable 'append' mode, see this: http://stackoverflow.com/questions/1225146/java-filewriter-with-append-mode — steenbergh, Mar 19 '15 at 09:18
@immibis: `writeHere.close()` is present in the sample code - although admittedly it would be better to use a try-with-resources block. — Jon Skeet, Mar 19 '15 at 09:18
@JonSkeet The *other* FileWriter. (Wow, correcting Jon Skeet...) Also, it's a rhetorical question since the answer is plainly obvious in the code. — user253751, Mar 19 '15 at 09:19

ivan.mylyanyk · Accepted Answer · 2015-03-19T09:22:42.073

5

Pass true as a second argument to FileWriter to turn on "append" mode (in the first FileWriter you have created).

Also, you should create the variable FileWriter, and close it after appending "List:", as you leave the scope of that variable.

So, I would edit the code as following:

File hi = new File("hi.txt");
try {
    if (!hi.exists()) {
        System.out.printf("\nCreating 'hi.txt'.");
        hi.createNewFile();
        String hello = "List:";
        FileWriter writer = new FileWriter(hi, true);
        writer.append(hello);
        writer.close();
    } else {
        System.out.printf("\nWriting to 'hi.txt'");
    }
    FileWriter writeHere = new FileWriter(hi, true);
    String uling = "hi";
    writeHere.append(uling);
    writeHere.close();
}
//error catching
catch (IOException e) {
    System.out.printf("\nError. Check the file 'hi.txt'.");
}

NOTICE: Modifications at lines 7-9.

http://docs.oracle.com/javase/7/docs/api/java/io/FileWriter.html

edited Mar 19 '15 at 09:22

answered Mar 19 '15 at 09:17

ivan.mylyanyk

2,051
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You mean like `FileWriter writeHere = new FileWriter(hi, true);` in the sample code? – Jon Skeet Mar 19 '15 at 09:17
@JonSkeet no, I mean a few lines above - where Steve tries to append "List:". – ivan.mylyanyk Mar 19 '15 at 09:18
Thanks! It solved the problem. Just a quick question though, why should the filewriter always be closed after every single write? I get that closing it is needed, but why not close it after all the writes are done? – Steve Mar 19 '15 at 09:31
1

@GoogleHireMe: But this a file that doesn't exist beforehand (`if (!hi.exists())`) so why would that make a difference? I suspect the *actual* difference is just that you're closing the writer... – Jon Skeet Mar 19 '15 at 09:36
@Steve apparently, you can close it once in the end (when everything is done), but you have to close *every* instance of FileWriter. In your case - you have two FileWriters (one in the If-scope, and one after *if*). Of course, you can define only one FileWriter (above if-scope) and use it in both places. And then close only once before leaving try block. – ivan.mylyanyk Mar 19 '15 at 09:37
@JonSkeet oh, right. Make sense. Missed that part that the file will be empty at that point. – ivan.mylyanyk Mar 19 '15 at 09:39
@GoogleHireMe If it has to be closed at every scope and level, is there any way to close it all with just one `writeHere.close();` ? If so, I can move `FileWriter writeHere = new FileWriter(hi, true);` to line 2 and just write `writeHere.append(hello);` at line 7. – Steve Mar 19 '15 at 09:42
@Steve no, because you aren't closing the `FileWriter` which you have instantiated in the line `new FileWriter(hi).append(hello")`. Notice the keyword `new` here, which means creating new instance. You are using `new FileWriter()` twice in your code, which means you have two instances. And this means that you have to close both of them. – ivan.mylyanyk Mar 19 '15 at 09:45
@Steve: This sort of problem is exactly why I've suggested simplifying the code to only have one writer, regardless of whether the file's new or not. See my answer. – Jon Skeet Mar 19 '15 at 09:54
@Steve yes, I have seen. Of course, your solution is more pretty, but it almost completely changes initial code :) – ivan.mylyanyk Mar 19 '15 at 10:04

score 3 · Answer 2 · answered Mar 19 '15 at 09:40

The problem is with this line:

new FileWriter(hi).append(hello);

You're not closing the writer, which means:

The file handle is potentially still open, which could cause problems when you try to write to it
You're not flushing the writer, so the input may get lost

You should also get in the habit of using try-with-resources to acquire and then automatically close the writer, even if an exception occurs.

Personally, I'd change the structure of your code somewhat so you only open the file once:

File hi = new File("hi.txt");
boolean newFile = !hi.exists();
System.out.printf("%n%s 'hi.txt'.", newFile ? "Creating" : "Writing to");
try (Writer writer = new FileWriter(hi, true)) {
    // Note: if you've already got a string, you might as well use write...
    if (newFile) {
        writer.write("List:");
    }
    writer.write(uling);
}
catch(IOException e) {
  System.out.printf("\nError. Check the file 'hi.txt'.");
}

score 0 · Answer 3 · answered Feb 05 '18 at 15:42

0

It is very important not to forget to close the writer. Well, if you do not close it, it will not be written.

writer.close().

answered Feb 05 '18 at 15:42

Anxo P

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Filewriter will not append text to newly created file

3 Answers3