Get the file being written by FileWriter in Java

Question

Is there a way that i can Get the file it being written in case of FileWirter. I dont have any reference to the File object with me.

public class JobResponseWriter extends FileWriter{
    public JobResponseWriter(Job job) throws IOException {
        super(File.createTempFile("JobResponse" + job.getId() ,"tmp"));
    }

    public void writeLn(String str) throws IOException {
        super.write(str + "\n");
    }
}

How can I get the File that got created in this case. I will access thefile only after the writer is closed..But i dont want to keep a separate list of all the file created. Whats the best way.

Do you have to use the super constructor to create the temp file? — OneCricketeer, Dec 03 '16 at 11:07
I need the JobResponseWriter to behave as A FileWriter, If you have any other way..to that let me know — Ysak, Dec 03 '16 at 11:07
This is a standard problem of "Composition over inheritance". You should make a `File` member variable and "simulate" the Filewriter class instead of directly extending it — OneCricketeer, Dec 03 '16 at 11:12
Alright...i got it...is there a way i can Find the File from FileWriter instance ?? — Ysak, Dec 03 '16 at 11:15
If you could get the file, what exactly would you want to do with it? — OneCricketeer, Dec 03 '16 at 11:25

Patrick Parker · Accepted Answer · 2016-12-03T14:07:48.697

2

You just need to save a reference to the File:

public class JobResponseWriter extends FileWriter{
    private final File myFile;
    public JobResponseWriter(Job job) throws IOException {
        this(File.createTempFile("JobResponse" + job.getId() ,"tmp"));
    }
    public JobResponseWriter(File f) throws IOException {
        super(f);
        myFile = f;
    }
    /* your code here */
}

edited Dec 03 '16 at 14:07

answered Dec 03 '16 at 11:41

Patrick Parker

4,863
4
19
51

Ah, yeah. Wasn't thinking about that way – OneCricketeer Dec 03 '16 at 12:09
This is what exactly i have implemented..basically the file creation logic i have taken out... – Ysak Dec 03 '16 at 12:13

score 1 · Answer 2 · edited May 23 '17 at 12:08

Since you can't get the file before the super call

Initialize field before super constructor runs?

You could try something like this

public class JobResponseWriter {

    private final File f;
    private final fw;

    public JobResponseWriter(Job job) throws IOException {
        this.f = File.createTempFile("JobResponse" + job.getId() ,"tmp"));
        this.fw = new FileWriter(f);
    }

    public void writeLn(String str) throws IOException {
        fw.write(str + "\n");
    }

    // public void getFile() 
}

You may want to implement these interfaces if you want the full functionality of a filewriter-like object

Closeable, Flushable, Appendable, AutoCloseable

quartzsaber · Answer 3 · 2016-12-03T11:42:30.660

-1

According to the official document, there is no way to retrive the File object. And it's also not possible with FileWriter. However, by seeing the problm from a different perspective, you may come up like this (Assuming Job is your class. You can extend from Job if it's not):

public class JobResponseWriter extends FileWriter{
    File jobResponse = null;
    public FileWriter getJobResponseWriter() {
        if(jobResponse == null)
            jobResponse = File.createTempFile("JobResponse" + getId() ,"tmp"));
        return new FileWriter(jobResponse, true); //Open in append mode
    }

    public File getJobResponseFile() {
        if(jobResponse == null)
            jobResponse = File.createTempFile("JobResponse" + getId() ,"tmp"));
        return jobResponse;
    }

    //And the original methods here
}

edited Dec 03 '16 at 11:42

answered Dec 03 '16 at 11:19

quartzsaber

174
3
10

Um... Wait. I think I got confused with C++. Possibily not like that, but inside the method ``. I'll come back after checking it. – quartzsaber Dec 03 '16 at 11:26
This is not possible solution in Java – Ysak Dec 03 '16 at 11:39
@Ysak So I edited the code. I saw the problem from a different perspective. And it definitely should work. – quartzsaber Dec 03 '16 at 11:43
@cricket_007 - it's not necessary to initialize before the super call. it's enough to initialize afterwards. see my answer – Patrick Parker Dec 03 '16 at 11:49

Get the file being written by FileWriter in Java

3 Answers3