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The Apache Commons IO library contains utility classes, stream implementations, file filters,
file comparators, endian transformation classes, and much more.
/*
* 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.commons.io.input;
import static org.apache.commons.io.IOUtils.EOF;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.charset.Charset;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;
/**
* Simple implementation of the unix "tail -f" functionality.
*
* 1. Create a TailerListener implementation
*
* First you need to create a {@link TailerListener} implementation
* ({@link TailerListenerAdapter} is provided for convenience so that you don't have to
* implement every method).
*
*
* For example:
*
* public class MyTailerListener extends TailerListenerAdapter {
* public void handle(String line) {
* System.out.println(line);
* }
* }
*
* 2. Using a Tailer
*
*
* You can create and use a Tailer in one of three ways:
*
*
* - Using one of the static helper methods:
*
* - {@link Tailer#create(File, TailerListener)}
* - {@link Tailer#create(File, TailerListener, long)}
* - {@link Tailer#create(File, TailerListener, long, boolean)}
*
*
* - Using an {@link java.util.concurrent.Executor}
* - Using an {@link Thread}
*
*
*
* An example of each of these is shown below.
*
*
* 2.1 Using the static helper method
*
*
* TailerListener listener = new MyTailerListener();
* Tailer tailer = Tailer.create(file, listener, delay);
*
* 2.2 Using an Executor
*
*
* TailerListener listener = new MyTailerListener();
* Tailer tailer = new Tailer(file, listener, delay);
*
* // stupid executor impl. for demo purposes
* Executor executor = new Executor() {
* public void execute(Runnable command) {
* command.run();
* }
* };
*
* executor.execute(tailer);
*
*
*
* 2.3 Using a Thread
*
* TailerListener listener = new MyTailerListener();
* Tailer tailer = new Tailer(file, listener, delay);
* Thread thread = new Thread(tailer);
* thread.setDaemon(true); // optional
* thread.start();
*
* 3. Stopping a Tailer
* Remember to stop the tailer when you have done with it:
*
* tailer.stop();
*
*
* 4. Interrupting a Tailer
* You can interrupt the thread a tailer is running on by calling {@link Thread#interrupt()}.
*
* thread.interrupt();
*
* If you interrupt a tailer, the tailer listener is called with the {@link InterruptedException}.
*
* The file is read using the default charset; this can be overriden if necessary
* @see TailerListener
* @see TailerListenerAdapter
* @version $Id: Tailer.java 1714076 2015-11-12 16:06:41Z krosenvold $
* @since 2.0
* @since 2.5 Updated behavior and documentation for {@link Thread#interrupt()}
*/
public class Tailer implements Runnable {
private static final int DEFAULT_DELAY_MILLIS = 1000;
private static final String RAF_MODE = "r";
private static final int DEFAULT_BUFSIZE = 4096;
// The default charset used for reading files
private static final Charset DEFAULT_CHARSET = Charset.defaultCharset();
/**
* Buffer on top of RandomAccessFile.
*/
private final byte inbuf[];
/**
* The file which will be tailed.
*/
private final File file;
/**
* The character set that will be used to read the file.
*/
private final Charset cset;
/**
* The amount of time to wait for the file to be updated.
*/
private final long delayMillis;
/**
* Whether to tail from the end or start of file
*/
private final boolean end;
/**
* The listener to notify of events when tailing.
*/
private final TailerListener listener;
/**
* Whether to close and reopen the file whilst waiting for more input.
*/
private final boolean reOpen;
/**
* The tailer will run as long as this value is true.
*/
private volatile boolean run = true;
/**
* Creates a Tailer for the given file, starting from the beginning, with the default delay of 1.0s.
* @param file The file to follow.
* @param listener the TailerListener to use.
*/
public Tailer(final File file, final TailerListener listener) {
this(file, listener, DEFAULT_DELAY_MILLIS);
}
/**
* Creates a Tailer for the given file, starting from the beginning.
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
*/
public Tailer(final File file, final TailerListener listener, final long delayMillis) {
this(file, listener, delayMillis, false);
}
/**
* Creates a Tailer for the given file, with a delay other than the default 1.0s.
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
*/
public Tailer(final File file, final TailerListener listener, final long delayMillis, final boolean end) {
this(file, listener, delayMillis, end, DEFAULT_BUFSIZE);
}
/**
* Creates a Tailer for the given file, with a delay other than the default 1.0s.
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen if true, close and reopen the file between reading chunks
*/
public Tailer(final File file, final TailerListener listener, final long delayMillis, final boolean end,
final boolean reOpen) {
this(file, listener, delayMillis, end, reOpen, DEFAULT_BUFSIZE);
}
/**
* Creates a Tailer for the given file, with a specified buffer size.
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param bufSize Buffer size
*/
public Tailer(final File file, final TailerListener listener, final long delayMillis, final boolean end,
final int bufSize) {
this(file, listener, delayMillis, end, false, bufSize);
}
/**
* Creates a Tailer for the given file, with a specified buffer size.
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen if true, close and reopen the file between reading chunks
* @param bufSize Buffer size
*/
public Tailer(final File file, final TailerListener listener, final long delayMillis, final boolean end,
final boolean reOpen, final int bufSize) {
this(file, DEFAULT_CHARSET, listener, delayMillis, end, reOpen, bufSize);
}
/**
* Creates a Tailer for the given file, with a specified buffer size.
* @param file the file to follow.
* @param cset the Charset to be used for reading the file
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen if true, close and reopen the file between reading chunks
* @param bufSize Buffer size
*/
public Tailer(final File file, final Charset cset, final TailerListener listener, final long delayMillis,
final boolean end, final boolean reOpen
, final int bufSize) {
this.file = file;
this.delayMillis = delayMillis;
this.end = end;
this.inbuf = new byte[bufSize];
// Save and prepare the listener
this.listener = listener;
listener.init(this);
this.reOpen = reOpen;
this.cset = cset;
}
/**
* Creates and starts a Tailer for the given file.
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param bufSize buffer size.
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener, final long delayMillis,
final boolean end, final int bufSize) {
return create(file, listener, delayMillis, end, false, bufSize);
}
/**
* Creates and starts a Tailer for the given file.
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen whether to close/reopen the file between chunks
* @param bufSize buffer size.
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener, final long delayMillis,
final boolean end, final boolean reOpen,
final int bufSize) {
return create(file, DEFAULT_CHARSET, listener, delayMillis, end, reOpen, bufSize);
}
/**
* Creates and starts a Tailer for the given file.
*
* @param file the file to follow.
* @param charset the character set to use for reading the file
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen whether to close/reopen the file between chunks
* @param bufSize buffer size.
* @return The new tailer
*/
public static Tailer create(final File file, final Charset charset, final TailerListener listener,
final long delayMillis, final boolean end, final boolean reOpen
,final int bufSize) {
final Tailer tailer = new Tailer(file, charset, listener, delayMillis, end, reOpen, bufSize);
final Thread thread = new Thread(tailer);
thread.setDaemon(true);
thread.start();
return tailer;
}
/**
* Creates and starts a Tailer for the given file with default buffer size.
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener, final long delayMillis,
final boolean end) {
return create(file, listener, delayMillis, end, DEFAULT_BUFSIZE);
}
/**
* Creates and starts a Tailer for the given file with default buffer size.
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @param end Set to true to tail from the end of the file, false to tail from the beginning of the file.
* @param reOpen whether to close/reopen the file between chunks
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener, final long delayMillis,
final boolean end, final boolean reOpen) {
return create(file, listener, delayMillis, end, reOpen, DEFAULT_BUFSIZE);
}
/**
* Creates and starts a Tailer for the given file, starting at the beginning of the file
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @param delayMillis the delay between checks of the file for new content in milliseconds.
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener, final long delayMillis) {
return create(file, listener, delayMillis, false);
}
/**
* Creates and starts a Tailer for the given file, starting at the beginning of the file
* with the default delay of 1.0s
*
* @param file the file to follow.
* @param listener the TailerListener to use.
* @return The new tailer
*/
public static Tailer create(final File file, final TailerListener listener) {
return create(file, listener, DEFAULT_DELAY_MILLIS, false);
}
/**
* Return the file.
*
* @return the file
*/
public File getFile() {
return file;
}
/**
* Gets whether to keep on running.
*
* @return whether to keep on running.
* @since 2.5
*/
protected boolean getRun() {
return run;
}
/**
* Return the delay in milliseconds.
*
* @return the delay in milliseconds.
*/
public long getDelay() {
return delayMillis;
}
/**
* Follows changes in the file, calling the TailerListener's handle method for each new line.
*/
public void run() {
RandomAccessFile reader = null;
try {
long last = 0; // The last time the file was checked for changes
long position = 0; // position within the file
// Open the file
while (getRun() && reader == null) {
try {
reader = new RandomAccessFile(file, RAF_MODE);
} catch (final FileNotFoundException e) {
listener.fileNotFound();
}
if (reader == null) {
Thread.sleep(delayMillis);
} else {
// The current position in the file
position = end ? file.length() : 0;
last = file.lastModified();
reader.seek(position);
}
}
while (getRun()) {
final boolean newer = FileUtils.isFileNewer(file, last); // IO-279, must be done first
// Check the file length to see if it was rotated
final long length = file.length();
if (length < position) {
// File was rotated
listener.fileRotated();
// Reopen the reader after rotation
try {
// Ensure that the old file is closed iff we re-open it successfully
final RandomAccessFile save = reader;
reader = new RandomAccessFile(file, RAF_MODE);
// At this point, we're sure that the old file is rotated
// Finish scanning the old file and then we'll start with the new one
try {
readLines(save);
} catch (IOException ioe) {
listener.handle(ioe);
}
position = 0;
// close old file explicitly rather than relying on GC picking up previous RAF
IOUtils.closeQuietly(save);
} catch (final FileNotFoundException e) {
// in this case we continue to use the previous reader and position values
listener.fileNotFound();
}
continue;
} else {
// File was not rotated
// See if the file needs to be read again
if (length > position) {
// The file has more content than it did last time
position = readLines(reader);
last = file.lastModified();
} else if (newer) {
/*
* This can happen if the file is truncated or overwritten with the exact same length of
* information. In cases like this, the file position needs to be reset
*/
position = 0;
reader.seek(position); // cannot be null here
// Now we can read new lines
position = readLines(reader);
last = file.lastModified();
}
}
if (reOpen) {
IOUtils.closeQuietly(reader);
}
Thread.sleep(delayMillis);
if (getRun() && reOpen) {
reader = new RandomAccessFile(file, RAF_MODE);
reader.seek(position);
}
}
} catch (final InterruptedException e) {
Thread.currentThread().interrupt();
stop(e);
} catch (final Exception e) {
stop(e);
} finally {
IOUtils.closeQuietly(reader);
}
}
/**
* Stops the tailer with an exception
* @param e The exception to send to listener
*/
private void stop(final Exception e) {
listener.handle(e);
stop();
}
/**
* Allows the tailer to complete its current loop and return.
*/
public void stop() {
this.run = false;
}
/**
* Read new lines.
*
* @param reader The file to read
* @return The new position after the lines have been read
* @throws java.io.IOException if an I/O error occurs.
*/
private long readLines(final RandomAccessFile reader) throws IOException {
ByteArrayOutputStream lineBuf = new ByteArrayOutputStream(64);
long pos = reader.getFilePointer();
long rePos = pos; // position to re-read
int num;
boolean seenCR = false;
while (getRun() && ((num = reader.read(inbuf)) != EOF)) {
for (int i = 0; i < num; i++) {
final byte ch = inbuf[i];
switch (ch) {
case '\n':
seenCR = false; // swallow CR before LF
listener.handle(new String(lineBuf.toByteArray(), cset));
lineBuf.reset();
rePos = pos + i + 1;
break;
case '\r':
if (seenCR) {
lineBuf.write('\r');
}
seenCR = true;
break;
default:
if (seenCR) {
seenCR = false; // swallow final CR
listener.handle(new String(lineBuf.toByteArray(), cset));
lineBuf.reset();
rePos = pos + i + 1;
}
lineBuf.write(ch);
}
}
pos = reader.getFilePointer();
}
IOUtils.closeQuietly(lineBuf); // not strictly necessary
reader.seek(rePos); // Ensure we can re-read if necessary
if (listener instanceof TailerListenerAdapter) {
((TailerListenerAdapter) listener).endOfFileReached();
}
return rePos;
}
}