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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 36825] New: - Enhance LockableFileWriter to handle different character endocings.
Date Tue, 27 Sep 2005 07:49:28 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=36825

           Summary: Enhance LockableFileWriter to handle different character
                    endocings.
           Product: Commons
           Version: 1.1 Final
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P2
         Component: IO
        AssignedTo: commons-dev@jakarta.apache.org
        ReportedBy: andylehane@hotmail.com


Hi,

LockableFileWriter needs to be enhanced so that it can support different
character encodings. Below is my attempt at introducing this functionality based
on the existing class:

(Also, should LockableFileWriter be a decoration class?)

Cheers,

Andy

-- START CLASS --

package com.sita.ats.io;

import java.io.*;

import org.apache.commons.lang.StringUtils;

/**
 * FileWriter that will create and honor lock files to allow simple
 * cross thread file lock handling and allow writing to a given encoding.
 * If <code>Writer</code> attributes
 * are unspecified, the default behavior is to overwrite (rather than
 * to iAppend), and to use the value of the system property
 * <code>java.io.tmpdir</code> for the lock file directory.
 *
 * @version $Id: ULockableFileWriter.java,v 1.1 2005/09/27 07:23:33 andyl Exp $
 * @author Andy Lehane
 */
public class ULockableFileWriter extends Writer {

    /** The extension for the lock file. */
    private static final String LCK = ".lck";
    /** The lock file. */
    private File iLockFile;   // Initialises to null
    /** The write used to write to the file. */
    private Writer iWriter;    // Initialises to null
    /** Should we append to the file or not. */
    private boolean iAppend; // Initialises to false
    /** The encoding to use. */
    private String iEncoding; // Initialises to null 
    
    /**
     * Constructs a LockableFileWriter. If the file exists, it is overwritten.
     * @param fileName file to write to
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final String fileName) throws IOException {
        this(fileName, null, false, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param fileName file to write to
     * @param append true if content should be appended (default is to overwrite).
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final String fileName, final boolean append)
throws IOException {
        this(fileName, null, append, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param fileName file to write to
     * @param append true if content should be appended (default is to overwrite).
     * @param lockDir Specifies the directory in which the lock file should be held.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final String fileName, final boolean append,
final String lockDir) throws IOException {
        this(new File(fileName), null, append, lockDir);
    }

    /**
     * Constructs a LockableFileWriter. If the file exists, it is overwritten.
     * @param file file to write to
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final File file) throws IOException {
        this(file, null, false, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param file file to write to
     * @param append true if content should be appended (default is to overwrite).
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final File file, final boolean append) throws
IOException {
        this(file, null, append, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param file file to write to
     * @param append true if content should be appended (default is to overwrite).
     * @param lockDir Specifies the directory in which the lock file should be held.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final File file, final boolean append, final
String lockDir) throws IOException {

        this(file, null, append, lockDir);
    }
    
    /**
     * Constructs a LockableFileWriter. If the file exists, it is overwritten.
     * @param fileName file to write to
     * @param encoding The encoding to use when writing.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(
            final String fileName,
            final String encoding) throws IOException {
        this(fileName, encoding, false, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param fileName file to write to
     * @param encoding The encoding to use when writing.
     * @param append true if content should be appended (default is to overwrite).
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(
            final String fileName, 
            final String encoding,
            final boolean append) throws IOException {
        this(fileName, encoding, append, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param fileName file to write to
     * @param encoding The encoding to use when writing.
     * @param append true if content should be appended (default is to overwrite).
     * @param lockDir Specifies the directory in which the lock file should be held.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(
            final String fileName,
            final String encoding,
            final boolean append,
            final String lockDir) throws IOException {
        this(new File(fileName), encoding, append, lockDir);
    }

    /**
     * Constructs a LockableFileWriter. If the file exists, it is overwritten.
     * @param file file to write to
     * @param encoding The encoding to use when writing.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(final File file, final String encoding) throws
IOException {
        this(file, encoding, false, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param file file to write to
     * @param encoding The encoding to use when writing.
     * @param append true if content should be appended (default is to overwrite).
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(
            final File file,
            final String encoding,
            final boolean append) throws IOException {
        this(file, encoding, append, null);
    }

    /**
     * Constructs a LockableFileWriter.
     * @param file file to write to
     * @param encoding The encoding to use when writing.
     * @param append true if content should be appended (default is to overwrite).
     * @param lockDir Specifies the directory in which the lock file should be held.
     * @throws IOException in case of an I/O error
     */
    public ULockableFileWriter(
            final File file,
            final String encoding,
            final boolean append,
            final String lockDir) throws IOException {
        
        super(file);
        iAppend = append;
        iEncoding = encoding;
        
        String lDir = lockDir;
        if (lDir == null) {
            lDir = System.getProperty("java.io.tmpdir");
        }
        testLockDir(new File(lDir));
        iLockFile = new File(lDir, file.getName() + LCK);
        createLock();
        
        try {
            if (StringUtils.isEmpty(encoding)) {
                iWriter = new FileWriter(file.getAbsolutePath(), iAppend);
            } else {
                
                if (file.getParentFile().exists() == false) {
                    file.getParentFile().mkdirs();
                }
                
                if (file.getAbsoluteFile().exists() == false) {
                    file.getAbsoluteFile().createNewFile();
                }
                
                iWriter = new OutputStreamWriter(new
FileOutputStream(file.getAbsolutePath(), iAppend), iEncoding);
            }
        } catch (IOException ioe) {
            iLockFile.delete();
            throw ioe;
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * Tests that we can write to the lock directory.
     * 
     * @param lockDir File representing the lock directory.
     * @throws IOException if we cannot write to the lock directory or cannot
file 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 (ULockableFileWriter.class) {
            if (!iLockFile.createNewFile()) {
                throw new IOException("Can't write file, lock " +
                    iLockFile.getAbsolutePath() + " exists");
            }
            iLockFile.deleteOnExit();
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * Close the stream, flushing it first.  Once a stream has been closed,
     * further write() or flush() invocations will cause an IOException to be
     * thrown.  Closing a previously-closed stream, however, has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void close() throws IOException {
        try {
            iWriter.close();
        } finally {
            iLockFile.delete();
        }
    }

    /**
     * Write a portion of a string.
     *
     * @param  cbuf  The characters to write
     * @param  off  Offset from which to start writing characters
     * @param  len  Number of characters to write
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void write(final char[] cbuf, final int off, final int len) throws
IOException {
        iWriter.write(cbuf, off, len);
    }

    /**
     * Flush the stream.  If the stream has saved any characters from the
     * various write() methods in a buffer, write them immediately to their
     * intended destination.  Then, if that destination is another character or
     * byte stream, flush it.  Thus one flush() invocation will flush all the
     * buffers in a chain of Writers and OutputStreams.
     * <p>
     * If the intended destination of this stream is an abstraction provided by
     * the underlying operating system, for example a file, then flushing the
     * stream guarantees only that bytes previously written to the stream are
     * passed to the operating system for writing; it does not guarantee that
     * they are actually written to a physical device such as a disk drive.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void flush() throws IOException {
        iWriter.flush();
    }
    
    //-----------------------------------------------------------------------
    /**
     * Gets the character encoding used when writing to the file. 
     * 
     * @return The encoding method.
     */
    public String getEncoding() {
        return iEncoding;
    }
}

-- END CLASS --

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