contrib code

[Michael Salmon]

hi folks,
I wrote this class for doing safe template.merge()'s with velocity so
that a file getting written wouldnt have two merges possibly
conflicting. Jon Stevens recommended it would fit better in
commons-sandbox rather then in velocity though, so here it is. 

thanks,
ms-

package org.apache.commons.util;

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 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
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 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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import java.io.File;
import java.io.Writer;
import java.io.FileWriter;
import java.io.IOException;

/**
 * FileWriter that will create and honor lock files to allow simple 
 * cross thread file lock handling.
 *
 * @author <a href="mailto:[EMAIL PROTECTED]";>Michael Salmon</a>
 * @version $Id$
 */
public class SafeFileWriter extends Writer
{
    private String lockDir = "";
    private boolean useHiddenLocks = false;
    private File lockFile = null;
    private final String LCK = ".lck";

    private FileWriter writer = null;
    private final String DIR_SEPERATOR = System.getProperty("file.seperator");

    public SafeFileWriter (String fileName)
        throws IOException
    {
        createLock(lockDir + fileName);
        this.writer = new FileWriter(fileName);
    }

    public SafeFileWriter (String fileName, boolean append)
        throws IOException
    {
        createLock(fileName);
        this.writer = new FileWriter(fileName, append);
    }

    public SafeFileWriter (File file)
        throws IOException
    {
        createLock(lockDir + file.getPath() + ".lck");
        this.writer = new FileWriter(file);
    }
    
    private void createLock(String lockPath)
        throws IOException
    {
        synchronized(SafeFileWriter.class)
        {
            if (new File(lockPath).exists())
            {
                throw new IOException("Can't write file, " + lockPath + " exists");
            }
            if (useHiddenLocks)
            {
                lockFile = new File(lockDir + DIR_SEPERATOR + "." + lockPath + LCK);
            }
            else
            {
                lockFile = new File(lockDir + DIR_SEPERATOR + lockPath + LCK);
            }
        }
    }

    /**
     * Sets directory to place lock files in.
     * Default is directory that file is located in.
     * @param String directory to place lock files in.
     */
    public void setLockDir (String lockDir)
    {
        this.lockDir = lockDir;
    }

    /**
     * Determines whether to use filenames starting with "." 
     * so that on unix-like systems they will act as hidden.
     * @param boolean useHiddenFiles or not
     */
    public void setUseHiddenLocks (boolean useHiddenLocks)
    {
        this.useHiddenLocks = useHiddenLocks;
    }

    public void unlock()
        throws IOException
    {
        lockFile.delete();
    }

    public void write(char [] cbuf, int off, int len)
        throws IOException
    {
        writer.write(cbuf, off, len);
    }

    public void flush()
        throws IOException
    {
        writer.flush();
    }

    public void close()
        throws IOException
    {
       writer.close();
    } 
}