Gary Gary - 1 month ago 14
Java Question

Java IO implementation of unix/linux "tail -f"

I'm wondering what techniques and/or library to use to implement the functionality of the linux command "tail -f ". I'm essentially looking for a drop in add-on/replacement for

java.io.FileReader
. Client code could look something like this:

TailFileReader lft = new TailFileReader("application.log");
BufferedReader br = new BufferedReader(lft);
String line;
try {
while (true) {
line= br.readLine();
// do something interesting with line
}
} catch (IOException e) {
// barf
}


The missing piece is a reasonable implementation of
TailFileReader
. It should be able to read parts of the file that exist before the file is opened as well as the lines that are added.

Answer

The ability to continue to read a file, and wait around until the file has some more updates for you shouldn't be that hard to accomplish in code yourself. Here's some pseudo-code:

BufferedReader br = new BufferedReader(...);
String line;
while (keepReading) {
    line = reader.readLine();
    if (line == null) {
        //wait until there is more of the file for us to read
        Thread.sleep(1000);
    }
    else {
        //do something interesting with the line
    }
}

I would assume that you would want to put this type of functionality in its own Thread, so that you can sleep it and not affect any other areas of your application. You would want to expose keepReading in a setter so that your main class / other parts of the application can safely shut the thread down without any other headaches, simply by calling stopReading() or something similar.