org.apache.commons.io.output.LockableFileWriter Maven / Gradle / Ivy
/*
* 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.output;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.Charset;
import org.apache.commons.io.Charsets;
import org.apache.commons.io.FileUtils;
/**
* FileWriter that will create and honor lock files to allow simple
* cross thread file lock handling.
*
* This class provides a simple alternative to FileWriter
* that will use a lock file to prevent duplicate writes.
*
* N.B. the lock file is deleted when {@link #close()} is called
* - or if the main file cannot be opened initially.
* In the (unlikely) event that the lockfile cannot be deleted,
* this is not reported, and subsequent requests using
* the same lockfile will fail.
*
* By default, the file will be overwritten, but this may be changed to append.
* The lock directory may be specified, but defaults to the system property
* java.io.tmpdir.
* The encoding may also be specified, and defaults to the platform default.
*
*/
public class LockableFileWriter extends Writer {
// Cannot extend ProxyWriter, as requires writer to be
// known when super() is called
/** The extension for the lock file. */
private static final String LCK = ".lck";
/** The writer to decorate. */
private final Writer out;
/** The lock file. */
private final File lockFile;
/**
* Constructs a LockableFileWriter.
* If the file exists, it is overwritten.
*
* @param fileName the file to write to, not null
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
*/
public LockableFileWriter(final String fileName) throws IOException {
this(fileName, false, null);
}
/**
* Constructs a LockableFileWriter.
*
* @param fileName file to write to, not null
* @param append true if content should be appended, false to overwrite
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
*/
public LockableFileWriter(final String fileName, final boolean append) throws IOException {
this(fileName, append, null);
}
/**
* Constructs a LockableFileWriter.
*
* @param fileName the file to write to, not null
* @param append true if content should be appended, false to overwrite
* @param lockDir the directory in which the lock file should be held
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
*/
public LockableFileWriter(final String fileName, final boolean append, final String lockDir) throws IOException {
this(new File(fileName), append, lockDir);
}
/**
* Constructs a LockableFileWriter.
* If the file exists, it is overwritten.
*
* @param file the file to write to, not null
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
*/
public LockableFileWriter(final File file) throws IOException {
this(file, false, null);
}
/**
* Constructs a LockableFileWriter.
*
* @param file the file to write to, not null
* @param append true if content should be appended, false to overwrite
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
*/
public LockableFileWriter(final File file, final boolean append) throws IOException {
this(file, append, null);
}
/**
* Constructs a LockableFileWriter.
*
* @param file the file to write to, not null
* @param append true if content should be appended, false to overwrite
* @param lockDir the directory in which the lock file should be held
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
* @deprecated 2.5 use {@link #LockableFileWriter(File, Charset, boolean, String)} instead
*/
@Deprecated
public LockableFileWriter(final File file, final boolean append, final String lockDir) throws IOException {
this(file, Charset.defaultCharset(), append, lockDir);
}
/**
* Constructs a LockableFileWriter with a file encoding.
*
* @param file the file to write to, not null
* @param encoding the encoding to use, null means platform default
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
* @since 2.3
*/
public LockableFileWriter(final File file, final Charset encoding) throws IOException {
this(file, encoding, false, null);
}
/**
* Constructs a LockableFileWriter with a file encoding.
*
* @param file the file to write to, not null
* @param encoding the encoding to use, null means platform default
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
* @throws java.nio.charset.UnsupportedCharsetException
* thrown instead of {@link java.io.UnsupportedEncodingException} in version 2.2 if the encoding is not
* supported.
*/
public LockableFileWriter(final File file, final String encoding) throws IOException {
this(file, encoding, false, null);
}
/**
* Constructs a LockableFileWriter with a file encoding.
*
* @param file the file to write to, not null
* @param encoding the encoding to use, null means platform default
* @param append true if content should be appended, false to overwrite
* @param lockDir the directory in which the lock file should be held
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
* @since 2.3
*/
public LockableFileWriter(File file, final Charset encoding, final boolean append,
String lockDir) throws IOException {
super();
// init file to create/append
file = file.getAbsoluteFile();
if (file.getParentFile() != null) {
FileUtils.forceMkdir(file.getParentFile());
}
if (file.isDirectory()) {
throw new IOException("File specified is a directory");
}
// init lock file
if (lockDir == null) {
lockDir = System.getProperty("java.io.tmpdir");
}
final File lockDirFile = new File(lockDir);
FileUtils.forceMkdir(lockDirFile);
testLockDir(lockDirFile);
lockFile = new File(lockDirFile, file.getName() + LCK);
// check if locked
createLock();
// init wrapped writer
out = initWriter(file, encoding, append);
}
/**
* Constructs a LockableFileWriter with a file encoding.
*
* @param file the file to write to, not null
* @param encoding the encoding to use, null means platform default
* @param append true if content should be appended, false to overwrite
* @param lockDir the directory in which the lock file should be held
* @throws NullPointerException if the file is null
* @throws IOException in case of an I/O error
* @throws java.nio.charset.UnsupportedCharsetException
* thrown instead of {@link java.io.UnsupportedEncodingException} in version 2.2 if the encoding is not
* supported.
*/
public LockableFileWriter(final File file, final String encoding, final boolean append,
final String lockDir) throws IOException {
this(file, Charsets.toCharset(encoding), append, lockDir);
}
//-----------------------------------------------------------------------
/**
* Tests that we can write to the lock directory.
*
* @param lockDir the File representing the lock directory
* @throws IOException if we cannot write to the lock directory
* @throws IOException if we cannot find the lock file
*/
private void testLockDir(final File lockDir) throws IOException {
if (!lockDir.exists()) {
throw new IOException(
"Could not find lockDir: " + lockDir.getAbsolutePath());
}
if (!lockDir.canWrite()) {
throw new IOException(
"Could not write to lockDir: " + lockDir.getAbsolutePath());
}
}
/**
* Creates the lock file.
*
* @throws IOException if we cannot create the file
*/
private void createLock() throws IOException {
synchronized (LockableFileWriter.class) {
if (!lockFile.createNewFile()) {
throw new IOException("Can't write file, lock " +
lockFile.getAbsolutePath() + " exists");
}
lockFile.deleteOnExit();
}
}
/**
* Initialise the wrapped file writer.
* Ensure that a cleanup occurs if the writer creation fails.
*
* @param file the file to be accessed
* @param encoding the encoding to use
* @param append true to append
* @return The initialised writer
* @throws IOException if an error occurs
*/
private Writer initWriter(final File file, final Charset encoding, final boolean append) throws IOException {
final boolean fileExistedAlready = file.exists();
try {
return new OutputStreamWriter(new FileOutputStream(file.getAbsolutePath(), append),
Charsets.toCharset(encoding));
} catch (final IOException | RuntimeException ex) {
FileUtils.deleteQuietly(lockFile);
if (fileExistedAlready == false) {
FileUtils.deleteQuietly(file);
}
throw ex;
}
}
//-----------------------------------------------------------------------
/**
* Closes the file writer and deletes the lockfile (if possible).
*
* @throws IOException if an I/O error occurs
*/
@Override
public void close() throws IOException {
try {
out.close();
} finally {
lockFile.delete();
}
}
//-----------------------------------------------------------------------
/**
* Write a character.
* @param idx the character to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(final int idx) throws IOException {
out.write(idx);
}
/**
* Write the characters from an array.
* @param chr the characters to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(final char[] chr) throws IOException {
out.write(chr);
}
/**
* Write the specified characters from an array.
* @param chr the characters to write
* @param st The start offset
* @param end The number of characters to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(final char[] chr, final int st, final int end) throws IOException {
out.write(chr, st, end);
}
/**
* Write the characters from a string.
* @param str the string to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(final String str) throws IOException {
out.write(str);
}
/**
* Write the specified characters from a string.
* @param str the string to write
* @param st The start offset
* @param end The number of characters to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(final String str, final int st, final int end) throws IOException {
out.write(str, st, end);
}
/**
* Flush the stream.
* @throws IOException if an I/O error occurs
*/
@Override
public void flush() throws IOException {
out.flush();
}
}