Apache Commons IO Tailer example

java apache-commons-io
user2435860 picture user2435860 · Apr 10, 2014 · Viewed 14.5k times · Source

I am working on a monitoring program that reads the /var/log/auth.log file. I am using Apache Commons IO Tailer class to read the file in real time. To get started, I wanted to test the real-time reading part on a simple file, and manually enter some code in the console line. Here is my code:

public class Main {
    public static void main(String[] args) {
        TailerListener listener = new MyListener();
        Tailer tailer = Tailer.create(new File("log.txt"), listener, 500);
        while(true) {

        }
    }
}

public class MyListener extends TailerListenerAdapter {
    @Override
    public void handle(String line) {
        System.out.println(line);
    }
}

And from the terminal : sudo echo "Hello" >> log.txt The problem is when I try to write manually something in the file, it does not print it in the console. I tried to find a concrete example of usage of Tailer class, but no luck. What am I doing wrong here?

Answer

Duncan Jones picture Duncan Jones · Apr 10, 2014

Based on my testing, Tailer will only print a line when you've added a newline to the file. So try sudo echo "Hello\n" >> log.txt

Also note that if you call create, you start a thread but have no handle on it. Hence why you had to have a while/true loop.

You could try this instead:

public static void main(String[] args) {
    TailerListener listener = new MyListener();
    Tailer tailer = new Tailer(new File("log.txt"), listener, 500);        
    tailer.run();
}

Related questions

Delete all files in directory (but not directory) - one liner solution

I want to delete all files inside ABC directory. When I tried with FileUtils.deleteDirectory(new File("C:/test/ABC/")); it also deletes folder ABC. Is there a one liner solution where I can delete files inside directory but not …

Read More
Is it safe to use Apache commons-io IOUtils.closeQuietly?

Is this code BufferedWriter bw = new BufferedWriter(new FileWriter("test.txt")); try { bw.write("test"); } finally { IOUtils.closeQuietly(bw); } safe or not? As far as I understand when we close a BufferedWriter it will flush its buffer to the underlying …

Read More
Reading a specific line from a text file in Java

Is there any method to read a specific line from a text file ? In the API or Apache Commons. Something like : String readLine(File file, int lineNumber) I agree it's trivial to implement, but it's not very efficient specially if …

Read More