File operations using Java are my favorite part. There are number of tutorials you may have seen on Crunchify like append data to file, read data from file, read and parse JSON file, read config.properties file during server startup, etc.
In this tutorial we will go over steps on how to implement linux tail -f command in Java. Java IO implementation of unix/linux “tail -f”. How can I follow a file like “Tail -f”?
Let’s get started:
- Create class
CrunchifyTailFOnLogFile_LogFileTailer.java - From main method start executor service to start log file tailer, i.e. crunchifyExecutor.execute(crunchify_tailF); which internally calls
run() - Also call
appendData()method which will add new line to file every5 seconds - Once new line will be added to file, tailer will pick and print it to Eclipse Console
package com.crunchify.tutorials;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.RandomAccessFile;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
*
* @author https://crunchify.com
*/
public class CrunchifyTailFOnLogFile_LogFileTailer implements Runnable {
private boolean debug = false;
private int crunchifyRunEveryNSeconds = 2000;
private long lastKnownPosition = 0;
private boolean shouldIRun = true;
private File crunchifyFile = null;
private static int crunchifyCounter = 0;
public CrunchifyTailFOnLogFile_LogFileTailer(String myFile, int myInterval) {
crunchifyFile = new File(myFile);
this.crunchifyRunEveryNSeconds = myInterval;
}
private void printLine(String message) {
System.out.println(message);
}
public void stopRunning() {
shouldIRun = false;
}
public void run() {
try {
while (shouldIRun) {
Thread.sleep(crunchifyRunEveryNSeconds);
long fileLength = crunchifyFile.length();
if (fileLength > lastKnownPosition) {
// Reading and writing file
RandomAccessFile readWriteFileAccess = new RandomAccessFile(crunchifyFile, "rw");
readWriteFileAccess.seek(lastKnownPosition);
String crunchifyLine = null;
while ((crunchifyLine = readWriteFileAccess.readLine()) != null) {
this.printLine(crunchifyLine);
crunchifyCounter++;
}
lastKnownPosition = readWriteFileAccess.getFilePointer();
readWriteFileAccess.close();
} else {
if (debug)
this.printLine("Hmm.. Couldn't found new line after line # " + crunchifyCounter);
}
}
} catch (Exception e) {
stopRunning();
}
if (debug)
this.printLine("Exit the program...");
}
public static void main(String argv[]) {
ExecutorService crunchifyExecutor = Executors.newFixedThreadPool(4);
// Replace username with your real value
// For windows provide different path like: c:\\temp\\crunchify.log
String filePath = "/Users/<username>/Downloads/crunchify.log";
CrunchifyTailFOnLogFile_LogFileTailer crunchify_tailF = new CrunchifyTailFOnLogFile_LogFileTailer(filePath, 2000);
// Start running log file tailer on crunchify.log file
crunchifyExecutor.execute(crunchify_tailF);
// Start pumping data to file crunchify.log file
appendData(filePath, true, 5000);
}
/**
* Use appendData method to add new line to file, so above tailer method can print the same in Eclipse Console
*
* @param filePath
* @param shouldIRun
* @param crunchifyRunEveryNSeconds
*/
private static void appendData(String filePath, boolean shouldIRun, int crunchifyRunEveryNSeconds) {
FileWriter fileWritter;
try {
while (shouldIRun) {
Thread.sleep(crunchifyRunEveryNSeconds);
fileWritter = new FileWriter(filePath, true);
BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
String data = "\nCrunchify.log file content: " + Math.random();
bufferWritter.write(data);
bufferWritter.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
Hope you find this Java implementation best suited for unix tail command. Here is a sample code to tail a log file using java.
Output:
Let me know if you have any trouble tailing file in Java. This is a simple tail program in Java.