Java 6 File Deletion

问题:

I am aware that this question is a raging duplicate of this question. However, I have now read that entire page twice, and some sections 3 times, and for the life of me I don't see how/where it is answered!

So, on to my problem.

I am at work and am stuck using Java 6 SE and cannot upgrade to 7. I am writing a program that creates a file, writes to it, does some processing, and then needs to delete the file out of existence. I am having the exact same problem as the person who asked the question I reference above: Java will not delete the file and I cannot figure out why.

The code:

File f = null;
FileWriter fw = null;
try
{
    f = new File("myFile.txt");
    fw = new FileWriter(f);
    fw.write("This is a sentence that should appear in the file.");
    fw.flush();
    if(f.delete())
        System.out.println("File was successfully deleted.");
    else
        System.err.println("File was not deleted.");
}
catch(Exception exc)
{
    System.err.println(exc.getMessage());
}
catch(Error er    {
    System.err.println(er.getMessage());
}
catch(Throwable t)
{
    System.err.println(t.getMessage());
}
finally
{
    fw.close();
}

It is not throwing any throwables, errors or exceptions (I included those to rule out any and all edge cases). The second print statement ("File was not deleted.") is being printed to the console. I am running this on Windows 7 and am writing to a folder where I have full permissions (rwx).

The user asking the question I referenced answered his own question, but does so (in my humble opinion) in a not-so-straight-forward way. In any case, I am having trouble making sense of it. He/she seems to be alluding to the fact that using a BufferedReader as opposed to a FileInputStream made the difference for him/her, but I just don't see how that applies.

Java 7 seems to have fixed this issues with the introduction of a java.nio.file.Files class, but again, I can't use Java 7 for reasons outside the scope of my control.

Other answerers to that referenced question allude that this is a "bug" in Java, and give all sorts of circumventions, such as explicitly calling System.gc(), etc. I have tried all of these and they are not working.

Maybe someone can add a fresh perspective and jog some thinking for me.

回答1:

You're trying to delete() a file which is still referenced by an active, open FileWriter.

Try this:

f = new File("myFile.txt");
fw = new FileWriter(f);
fw.write("This is a sentence that should appear in the file.");
fw.flush();
fw.close(); // actually free any underlying file handles.
if(f.delete())
    System.out.println("File was successfully deleted.");
else
    System.err.println("File was not deleted.");

回答2:

You can only delete the file if there is no file handler left opened. Since you open the file hanlder using FileWriter, you will need to close it before you can delete it. In other word, f.delete must be executed after fw.close

Try the code below. I made the changes to prevent all possible bug you may found, e.g if fw is null.

File f = null;
FileWriter fw = null;
try {
    f = new File("myFile.txt");
    fw = new FileWriter(f);
    fw.write("This is a sentence that should appear in the file.");
    fw.flush(); // flush is not needed if this is all your code does. you data
                // is automatically flushed when you close fw
} catch (Exception exc) {
    System.err.println(exc.getMessage());
} finally {// finally block is always executed.
    // fw may be null if an exception is raised in the construction 
    if (fw != null) {
        fw.close();
    }
    // checking if f is null is unneccessary. it is never be null.
    if (f.delete()) {
        System.out.println("File was successfully deleted.");
    } else {
        System.err.println("File was not deleted.");
    }
}