Java 随机访问文件

Question

    public void exportUrlsToFile(String file, String urls) throws IOException {
    String[] urlsArray = urls.split("\\s+");// split on one or more white space characters.

    // create a fresh file
    RandomAccessFile raf = new RandomAccessFile(file, "rw");

    for (String line : urlsArray) {
        line = line.trim();
        if (line.isEmpty()) {// this won't happen!
            continue;
        }
        raf.writeBytes(line);
        raf.writeBytes(newline);
    }
    // close the file handler
    raf.close();
}

Basically, I use this class to do something. This is part of the application that is running inside Tomcat JVM. I have noticed that anytime this method is called, it creates a file with the same name as the argument and after raf.close(), it is still there. How can I make sure that the temp file is removed?

Answer 1

A better question would be why you would want to go through all the trouble of making the file, writing things to the file, and then just delete the file?!

Regardless you don't need a random access file - a FileWriter would be better.

To ensure that the file is deleted do as Eddie suggests and put the delete in a finnaly block - but you will also need to ensure that the raf.close() IOException is handled... something like:

} finally {
    try
    {
        raf.close();
    }
    catch(final IOException ex)
    {
         // in 14 years of Java programming I still don't know what to do here! ;-)
    }
    finally
    {
        File todelete = new File(file);
        if (!todelete.delete()) {
            // Log a complaint that we couldn't delete the temp file
        }
    }
}

Edit:

You might also mean that after the Tomcat process finished the file is still there and you want it gone. If that is the case look at java.io.File.deleteOnExit(). That should delete the files when the Tomcat JVM exists.

Answer 2

I'm going to assume that you're showing only a small portion of the code and that there's a good reason that you're using RandomAccessFile when it doesn't appear that any random access is being done.

I would do something like this:

public void exportUrlsToFile(String file, String urls) throws IOException {
  String[] urlsArray = urls.split("\\s+");

  // create a fresh file
  RandomAccessFile raf = new RandomAccessFile(file, "rw");

  try {
    for (String line : urlsArray) {
      line = line.trim();
      if (line.isEmpty()) { // this won't happen!
        continue;
      }
      raf.writeBytes(line);
      raf.writeBytes(newline);
    }
  } finally {
    // don't leak file handles on Exception -- put close in "try/finally"
    try { raf.close(); } catch (IOException e) { /* ignore */ }
    File todelete = new File(file);
    if (!todelete.delete()) {
      // Log a complaint that we couldn't delete the temp file
    }
  }
}

EDIT: I agree, we don't want the theoretical IOException on close() to cause problem. Better than ignoring it would be to log a "We never expected to see this...." with the exception. I often create a closeWithoutException() method just to wrap this. Close theoretically throwing IOException seems an abuse of checked exceptions because there's nothing you can expect the caller to do in response.

Answer 3

Use File.createTempFile() instead?

I realize that won't give you the same features as RandomAccessFile but you could build what you need on top of that.

Actually I'm not even sure why you're writing these things to a file. Is this some kind of usage tracking thing? Why not just store it in memory?

Answer 4

Did you try this ?

 File temp = File.createTempFile("file", ".tmp");
 temp.deleteOnExit( );