DeferredFileOutputStream.java

/*
 * $Id$
 * $URL$
 */
package org.subethamail.common.io;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * This works like a ByteArrayOutputStream until a certain size is
 * reached, then creates a temp file and acts like a buffered
 * FileOutputStream.  The data can be retreived afterwards by
 * calling getInputStream().
 * 
 * When this object is closed, the temporary file is deleted.  You
 * can no longer call getInputStream().
 *  
 * @author Jeff Schnitzer
 */
public class DeferredFileOutputStream extends ThresholdingOutputStream
{
	/**
	 * Initial size of the byte array buffer.  Better to make this
	 * large to start with so that we can avoid reallocs; mail
	 * messages are rarely tiny.
	 */
	static final int INITIAL_BUF_SIZE = 8192;
	
	/** */
	public static final String TMPFILE_PREFIX = "subetha";
	public static final String TMPFILE_SUFFIX = ".msg";
	
	/** If we switch to file output, this is the file. */
	File outFile;
	
	/** If we switch to file output, this is the stream. */
	FileOutputStream outFileStream;
		
	/**
	 * @param transitionSize is the number of bytes at which to convert
	 *  from a byte array to a real file.
	 */
	public DeferredFileOutputStream(int transitionSize)
	{
		super(new BetterByteArrayOutputStream(INITIAL_BUF_SIZE), transitionSize);
	}

	/*
	 * (non-Javadoc)
	 * @see org.subethamail.common.io.ThresholdingOutputStream#thresholdReached(int, int)
	 */
	@Override
	protected void thresholdReached(int current, int predicted) throws IOException
	{
		// Open a temp file, write the byte array version, and swap the
		// output stream to the file version.
		
		this.outFile = File.createTempFile(TMPFILE_PREFIX, TMPFILE_SUFFIX);
		this.outFileStream = new FileOutputStream(this.outFile);

		((ByteArrayOutputStream)this.output).writeTo(this.outFileStream);
		
		this.output = new BufferedOutputStream(this.outFileStream);
	}
	
	/**
	 * Closes the output stream and creates an InputStream on the same data.
	 * 
	 * @return either a ByteArrayInputStream or buffered FileInputStream,
	 *  depending on what state we are in.  
	 */
	public InputStream getInputStream() throws IOException
	{
		if (this.output instanceof BetterByteArrayOutputStream)
		{
			return ((BetterByteArrayOutputStream)this.output).getInputStream();
		}
		else
		{
			this.output.flush();
			this.output.close();
			
			return new BufferedInputStream(new FileInputStream(this.outFile));
		}
	}

	/* (non-Javadoc)
	 * @see org.subethamail.common.io.ThresholdingOutputStream#close()
	 */
	@Override
	public void close() throws IOException
	{
		this.output.flush();
		this.output.close();
		
		this.outFile.delete();
	}

}