how to update certain parts of text file in java

问题

I want to be able to update a certain line on a text file. But I get the error that it cannot delete the file, why do I get this error?

public class Main {
    public static void main(String[] args) {
        Main rlf = new Main();
        rlf.removeLineFromFile("F:\\text.txt", "bbb");
    }

    public void removeLineFromFile(String file, String lineToRemove) {
        try {
            File inFile = new File(file);

            if (!inFile.isFile()) {
                System.out.println("Parameter is not an existing file");
                return;
            }

            //Construct the new file that will later be renamed to the original filename.
            File tempFile = new File(inFile.getAbsolutePath() + ".tmp");

            BufferedReader br = new BufferedReader(new FileReader(file));
            PrintWriter pw = new PrintWriter(new FileWriter(tempFile));

            String line = null;

            //Read from the original file and write to the new
            //unless content matches data to be removed.
            while ((line = br.readLine()) != null) {

                if (!line.trim().equals(lineToRemove)) {

                    pw.println(line);
                    pw.flush();
                }
            }
            pw.close();
            br.close();

            //Delete the original file
            if (!inFile.delete()) {
                System.out.println("Could not delete file");
                return;
            }

            //Rename the new file to the filename the original file had.
            if (!tempFile.renameTo(inFile)) System.out.println("Could not rename file");

        }
        catch (FileNotFoundException ex) {
            ex.printStackTrace();
        }
        catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

回答1:

The program works for me. Perhaps you are having an environmental issue.

回答2:

You should look into RandomAccessFile.

This will let you seek to the place in the file you want, and only update the part that you want to update.

回答3:

As Justin pointed out above, you should be using the RandomAccessFile kind of api if you want to modify parts of file. The approach you are trying to use has a lot of potential problems.

It requires a tmp file to be created in addition. May not scale for large files (I am not aware of your problem domain, though)
Trying to juggle files also can cause several potential exceptions, and requires lots of error handling.

回答4:

You can create a new instance (to close the old) by new then delete using it.
Same file delete problem here

来源：https://stackoverflow.com/questions/3878372/how-to-update-certain-parts-of-text-file-in-java

标签

java

text-files

bufferedreader