删除和重命名文件

Question

So I'm trying to delete a line of data from a file, which I have successfully done by opening a new file and writing all the information that doesn't match with the data that I would like to remove. The problem is, after I have done that, I would like to delete my original file, and then rename the new file with excludes the information I wanted to delete, to the same name as the original file. I have added in the code to do this, but for some reason it's not working.

public static void delete() throws IOException
{
    File inputFile = new File("Elements.txt");
    File tempFile = new File("myTempFile.txt");

    BufferedReader reader = new BufferedReader(new FileReader(inputFile));
    BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));

    String element = JOptionPane.showInputDialog(null, "Enter the name of the Element you wish to delete.", "Remove an Element.", JOptionPane.INFORMATION_MESSAGE);;
    String currentLine;

    while((currentLine = reader.readLine()) != null) {
        String trimmedLine = currentLine.trim();
        if(trimmedLine.startsWith(element)) continue;
        writer.write(currentLine + System.getProperty("line.separator"));
    }
    writer.close(); 
    reader.close(); 

    inputFile.delete();
    tempFile.renameTo(inputFile);

    JOptionPane.showMessageDialog(null, "Data has been removed from the file: Elements.txt");
}

As you can see near the bottom, I have these lines:

inputFile.delete();

tempFile.renameTo(inputFile);

These lines are meant to delete my original file(inputFile) and then rename my new file(tempFile) to the file name that the original file had. After running the code however, I simply get a file called "myTempFile.txt" which has succesfully deleted the line of data that I wanted, but my original file is still present and it wasn't deleted, neither was the new file renamed to the original file.

Any idea why this is happening?

Answer 1

Use the java.nio.file API . This is 2015.

final Path src = Paths.get("Elements.txt").toAbsolutePath();
final Path tmp = src.resolveSibling("Elements.txt.new");

try (
    final BufferedReader reader = Files.newBufferedReader(src, StandardCharsets.UTF_8);
    final BufferedWriter writer = Files.newBufferedWriter(tmp, StandardCharsets.UTF_8,
        StandardOpenOption.CREATE_NEW);
) {
    // yadda yadda
}

Files.move(tmp, src, StandardCopyOption.REPLACE_EXISTING);

File is unreliable . It has always been.

Answer 2

in such a case i would start fiddling around, reading documentation and maybe googling for a bit. But i will give you an answer, too!

inputFile.delete();

This could go wrong, for example if you have your file opened in a text editor. Luckily delete() returns a boolean, try checking that!

Also as Niels correctly mentioned File.renameTo() is quite unrelieble if you have access to Java 7 use the files.nio alternative. In Java 7 you can use Files.move(Path source, Path target, CopyOption... options)

Docs for Java 7 Files: http://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html

Answer 3

But your very code works correctly for me. I only change the path to the file and I make sure the file is not opened in editor

public class NewClass {

public static void main(String[] args) {
    try {
        delete();
    } catch (IOException ex) {
        Logger.getLogger(NewClass.class.getName()).log(Level.SEVERE, null, ex);
    }
}

public static void delete() throws IOException {
    File inputFile = new File("C:\\Users\\olyjosh\\Desktop\\Elements.txt");
    File tempFile = new File("C:\\Users\\olyjosh\\Desktop\\myTempFile.txt");

    BufferedReader reader = new BufferedReader(new FileReader(inputFile));
    BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));

    String element = JOptionPane.showInputDialog(null, "Enter the name of the Element you wish to delete.", "Remove an Element.", JOptionPane.INFORMATION_MESSAGE);;
    String currentLine;

    while ((currentLine = reader.readLine()) != null) {
        String trimmedLine = currentLine.trim();
        if (trimmedLine.startsWith(element)) {
            continue;
        }
        writer.write(currentLine + System.getProperty("line.separator"));
    }
    writer.close();
    reader.close();

    inputFile.delete();
    tempFile.renameTo(inputFile);

    JOptionPane.showMessageDialog(null, "Data has been removed from the file: Elements.txt");
}

}