/*
* 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.FileWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;
/**
* FileWriter that will create and honor lock files to allow simple
* cross thread file lock handling.
* <p>
* This class provides a simple alternative to <code>FileWriter</code>
* that will use a lock file to prevent duplicate writes.
* <p>
* <b>N.B.</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.
* <p>
* 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
* <code>java.io.tmpdir</code>.
* The encoding may also be specified, and defaults to the platform default.
*
* @author <a href="mailto:[email protected]">Scott Sanders</a>
* @author <a href="mailto:[email protected]">Michael Salmon</a>
* @author <a href="mailto:[email protected]">Jon S. Stevens</a>
* @author <a href="mailto:[email protected]">Daniel Rall</a>
* @author Stephen Colebourne
* @author Andy Lehane
* @version $Id: LockableFileWriter.java 1002182 2010-09-28 14:39:19Z sebb $
*/
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(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(String fileName, 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(String fileName, boolean append, 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(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(File file, 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
*/
public LockableFileWriter(File file, boolean append, String lockDir) throws IOException {
this(file, null, 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
*/
public LockableFileWriter(File file, 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
*/
public LockableFileWriter(File file, String encoding, 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");
}
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);
}
//-----------------------------------------------------------------------
/**
* 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(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(File file, String encoding, boolean append) throws IOException {
boolean fileExistedAlready = file.exists();
OutputStream stream = null;
Writer writer = null;
try {
if (encoding == null) {
writer = new FileWriter(file.getAbsolutePath(), append);
} else {
stream = new FileOutputStream(file.getAbsolutePath(), append);
writer = new OutputStreamWriter(stream, encoding);
}
} catch (IOException ex) {
IOUtils.closeQuietly(writer);
IOUtils.closeQuietly(stream);
FileUtils.deleteQuietly(lockFile);
if (fileExistedAlready == false) {
FileUtils.deleteQuietly(file);
}
throw ex;
} catch (RuntimeException ex) {
IOUtils.closeQuietly(writer);
IOUtils.closeQuietly(stream);
FileUtils.deleteQuietly(lockFile);
if (fileExistedAlready == false) {
FileUtils.deleteQuietly(file);
}
throw ex;
}
return writer;
}
//-----------------------------------------------------------------------
/**
* 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(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(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(char[] chr, int st, 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(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(String str, int st, 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();
}
}
|