code: /*
   * 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:sanders@apache.org">Scott Sanders</a>
   * @author <a href="mailto:ms@collab.net">Michael Salmon</a>
   * @author <a href="mailto:jon@collab.net">Jon S. Stevens</a>
   * @author <a href="mailto:dlr@finemaltcoding.com">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();
      }
  
  }
  