java.io gives you a mandatory file lock and java.nio gives you an advisory file lock
If you want to read any file without any lock you can use below classes
import java.nio.channels.FileChannel; import java.nio.file.Paths;
If you want to tail a file line by line use below code for the same
public void tail(String logPath){ String logStr = null; FileChannel fc = null; try { fc = FileChannel.open(Paths.get(logPath), StandardOpenOption.READ); fc.position(fc.size()); } catch (FileNotFoundException e1) { System.out.println("FileNotFoundException occurred in Thread : " + Thread.currentThread().getName()); return; } catch (IOException e) { System.out.println("IOException occurred while opening FileChannel in Thread : " + Thread.currentThread().getName()); } while (true) { try { logStr = readLine(fc); if (logStr != null) { System.out.println(logStr); } else { Thread.sleep(1000); } } catch (IOException|InterruptedException e) { System.out.println("Exception occurred in Thread : " + Thread.currentThread().getName()); try { fc.close(); } catch (IOException e1) { } break; } } } private String readLine(FileChannel fc) throws IOException { ByteBuffer buffers = ByteBuffer.allocate(128); // Standard size of a line assumed to be 128 bytes long lastPos = fc.position(); if (fc.read(buffers) > 0) { byte[] data = buffers.array(); boolean foundTmpTerminator = false; boolean foundTerminator = false; long endPosition = 0; for (byte nextByte : data) { endPosition++; switch (nextByte) { case -1: foundTerminator = true; break; case (byte) '\r': foundTmpTerminator = true; break; case (byte) '\n': foundTmpTerminator = true; break; default: if (foundTmpTerminator) { endPosition--; foundTerminator = true; } } if (foundTerminator) { break; } } fc.position(lastPos + endPosition); if (foundTerminator) { return new String(data, 0, (int) endPosition); } else { return new String(data, 0, (int) endPosition) + readLine(fc); } } return null; }
