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From: Roedy Green <see_website@mindprod.com.invalid>
Newsgroups: comp.lang.java.help
Subject: ByteArrayOutputStream gotcha
Date: Sun, 27 Nov 2011 14:41:08 -0800
Organization: Canadian Mind Products
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.help:1393

Here a SSCCE to point out a gotcha in ByteArrayOutputStream,
admittedly not the most commonly used class.   It is actually a bug.
What I have discovered conflicts with the documentation 

/*
 * [TestByteArrayOutputStream.java]
 *
 * Summary: Testing ByteArrayOutputStream
 *
 * Copyright: (c) 2011 Roedy Green, Canadian Mind Products,
http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any
purpose but military.
 *          http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.7+
 *
 * Created with: JetBrains IntelliJ IDEA IDE
http://www.jetbrains.com/idea/
 *
 * Version History:
 *  1.0 2011-11-27 initial version
 */
package com.mindprod.example;

import com.mindprod.common11.BigDate;
import org.apache.commons.io.output.ByteArrayOutputStream;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.zip.GZIPOutputStream;

import static java.lang.System.out;

/**
 * Testing ByteArrayOutputStream . Demonstrates gotcha and bug in
ByteArrayOutputStream class.
 * You must do a close() before the toByteArray. Docs suggest a flush
should be sufficient.
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.0 2011-11-27 initial version
 * @since 2011-11-27
 */
public final class TestByteArrayOutputStream
    {
    // -------------------------- STATIC METHODS
--------------------------

    /**
     * write an integer object to a file in compressed format
     *
     * @throws IOException if cannot write file
     */
    private static void writeToFile() throws IOException
        {
        // O P E N 
        final File o = new File( "temp.ser" );
        final FileOutputStream fos = new FileOutputStream( o );
        final OutputStream gzos = new GZIPOutputStream( fos, 1024/*
buffsize */ );
        final ObjectOutputStream oos = new ObjectOutputStream( gzos );
        // W R I T E
        oos.writeObject( new Integer( 149 ) );
        // F L U S H        
        oos.flush();
        // C L O S E
        oos.close();
        out.println( "file size: " + o.length() );
        }

    /**
     * write an integer object to a buffer in RAM in compressed format
     *
     * @throws IOException if cannot write file
     */
    private static void writeToRAM() throws IOException
        {
        // O P E N 
        final ByteArrayOutputStream baos = new ByteArrayOutputStream(
1024 );
        final OutputStream gzos = new GZIPOutputStream( baos, 1024/*
buffsize */ );
        final ObjectOutputStream oos = new ObjectOutputStream( gzos );
        // W R I T E
        oos.writeObject( new Integer( 149 ) );
        byte[] result0 = baos.toByteArray();
        out.println( "RAM result before flush " + result0.length + "
oops" );
        // F L U S H
        oos.flush();
        byte[] result1 = baos.toByteArray();
        out.println( "RAM result after flush " + result1.length + "
oops" );
        // C L O S E
        oos.close();
        // you don't get accurate results until AFTER the close!!
        byte[] result2 = baos.toByteArray();
        out.println( "RAM result after close " + result2.length + "
ok" );
        }

    // --------------------------- main() method
---------------------------

    /**
     * Testing ByteArrayOutputStream
     *
     * @param args not used
     */
    public static void main( String[] args ) throws IOException
        {
        writeToFile();
        writeToRAM();
        // output
        // file size: 94
        // RAM result before flush 10 oops
        // RAM result after flush 10 oops
        // RAM result after close 94 ok
        }
    }
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
How long till someone puts out a car navigator with the realistic
side comments of a real back seat driver.