| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| |
| package org.apache.sling.commons.log.logback.internal; |
| |
| import java.io.File; |
| import java.io.IOException; |
| import java.io.PrintWriter; |
| import java.io.RandomAccessFile; |
| |
| class Tailer{ |
| static final int BUFFER_SIZE = 1024; |
| private final int numOfLines; |
| private final TailerListener listener; |
| private final byte[] buffer = new byte[BUFFER_SIZE]; |
| |
| public Tailer(PrintWriter printWriter, int numOfLines) { |
| this(new PrinterListener(printWriter), numOfLines); |
| } |
| |
| public Tailer(TailerListener listener, int numOfLines) { |
| this.listener = listener; |
| this.numOfLines = numOfLines; |
| } |
| |
| interface TailerListener { |
| /** |
| * Handles a line from a Tailer. |
| * |
| * @param line the line. |
| */ |
| void handle(String line); |
| } |
| |
| public void tail(File file) throws IOException { |
| RandomAccessFile raf = null; |
| try{ |
| raf = new RandomAccessFile(file, "r"); |
| long startPos = getTailStartPos(raf, numOfLines); |
| readLines(raf, startPos); |
| } finally { |
| try{ |
| if (raf != null) { |
| raf.close(); |
| } |
| } catch (IOException ignore){ |
| |
| } |
| } |
| } |
| |
| /** |
| * Returns the starting position of UNIX "tail -n". |
| */ |
| private long getTailStartPos(RandomAccessFile file, int n) throws IOException { |
| int newlineCount = 0; |
| long length = file.length(); |
| long pos = length - BUFFER_SIZE; |
| int buffLength = BUFFER_SIZE; |
| |
| if (pos < 0) { |
| pos = 0; |
| buffLength = (int)length; |
| } |
| |
| while (true) { |
| file.seek(pos); |
| file.readFully(buffer, 0, buffLength); |
| |
| for (int i = buffLength - 1; i >= 0; i--) { |
| if ((char) buffer[i] == '\n') { |
| newlineCount++; |
| |
| if (newlineCount >= n) { |
| pos += (i + 1); |
| return pos; |
| } |
| } |
| } |
| |
| if (pos == 0) { |
| break; |
| } |
| |
| if (pos - BUFFER_SIZE < 0) { |
| buffLength = (int)pos; |
| pos = 0; |
| } else { |
| pos -= BUFFER_SIZE; |
| } |
| } |
| |
| return pos; |
| } |
| |
| /** |
| * Read new lines. Code below is taken from org.apache.commons.io.input.Tailer |
| * |
| * @throws java.io.IOException if an I/O error occurs. |
| * @param startPos position in file from where to start reading |
| */ |
| private void readLines(RandomAccessFile file, long startPos) throws IOException { |
| StringBuilder sb = new StringBuilder(); |
| |
| file.seek(startPos); |
| int num; |
| boolean seenCR = false; |
| while (((num = file.read(buffer)) != -1)) { |
| for (int i = 0; i < num; i++) { |
| byte ch = buffer[i]; |
| switch (ch) { |
| case '\n': |
| seenCR = false; // swallow CR before LF |
| listener.handle(sb.toString()); |
| sb.setLength(0); |
| break; |
| case '\r': |
| if (seenCR) { |
| sb.append('\r'); |
| } |
| seenCR = true; |
| break; |
| default: |
| if (seenCR) { |
| seenCR = false; // swallow final CR |
| listener.handle(sb.toString()); |
| sb.setLength(0); |
| } |
| sb.append((char) ch); // add character, not its ascii value |
| } |
| } |
| } |
| |
| //Drain the left over part |
| if (sb.length() != 0) { |
| listener.handle(sb.toString()); |
| } |
| } |
| |
| private static class PrinterListener implements Tailer.TailerListener { |
| private final PrintWriter pw; |
| |
| public PrinterListener(PrintWriter pw) { |
| this.pw = pw; |
| } |
| |
| @Override |
| public void handle(String line) { |
| pw.println(line); |
| } |
| } |
| |
| } |