Emulating Unix "tail -f" in Java
Implementing the functionality of the "tail -f" utility in Java involves finding an effective technique or library capable of monitoring a file for new additions and allowing the program to continuously read these new lines. To achieve this, consider the following approaches:
Apache Commons Tailer Class
A notable option is the Tailer class from Apache Commons IO. This class provides a straightforward solution for monitoring files and their modifications. It allows for continuous reading of new lines added to the file, similar to the behavior of "tail -f". Integration with the Tailer class can be achieved using the following code:
Tailer tailer = Tailer.create(new File("application.log"), new TailerListener() { @Override public void handle(String line) { // Perform desired operations on the newly added line } }); tailer.run();
Custom File Monitoring Implementation
Alternatively, one could create a custom file monitoring implementation that regularly checks for file size changes and updates its internal buffer accordingly. This approach requires a deeper understanding of file system behavior and event listening mechanisms within Java. Here's a simplified example:
import java.io.File; import java.io.IOException; import java.nio.file.*; import java.nio.file.attribute.BasicFileAttributes; public class TailFileMonitor implements Runnable { private File file; private long lastFileSize; public TailFileMonitor(File file) { this.file = file; this.lastFileSize = file.length(); } @Override public void run() { Path filePath = file.toPath(); try { WatchKey watchKey = filePath.getParent().register(new WatchService(), StandardWatchEventKinds.ENTRY_MODIFY); while (true) { WatchKey key = watchKey.poll(); if (key == watchKey) { for (WatchEvent> event : key.pollEvents()) { WatchEvent.Kind> kind = event.kind(); if (kind == StandardWatchEventKinds.ENTRY_MODIFY && event.context().toString().equals(file.getName())) { tailFile(); } } } key.reset(); } } catch (IOException e) { // Handle IO exceptions } } private void tailFile() { long currentFileSize = file.length(); if (currentFileSize != lastFileSize) { try (BufferedReader br = new BufferedReader(new FileReader(file))) { br.skip(lastFileSize); String line; while ((line = br.readLine()) != null) { // Process newly added lines } lastFileSize = currentFileSize; } catch (IOException e) { // Handle IO exceptions } } } }
To utilize the custom monitor, create an instance and execute it as a thread. It will constantly monitor the file for changes and update the buffer accordingly.
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