Compressed String (GZIPOutputStream) is not equal to the source string

Question

Hello,
I would like to compress the contents of a String (XML data) with the GZIPOutput/InputStream classes. Unfortunately I'm facing a problem - my source and result strings do not equal after the compression and decompression (I hope this is the correct sub-forum for this kind of question).
Here is a example code that reads data from a file (test.xml), compresses it via a GZIPOutputStream into compressed byte array and decompresses it back into a String:
public class CompressedStringTest {
     private static final String     FILENAME     = "test.xml";
     public CompressedStringTest() throws IOException {
          File file = new File( FILENAME );
          String xml = FileUtil.readFile( file );
          // COMPRESS
          ByteArrayOutputStream out = new ByteArrayOutputStream();
          GZIPOutputStream zipout = new GZIPOutputStream( out );
          zipout.write( xml.getBytes() );
          zipout.close();
          out.close();
          // DECOMPRESS
          byte[] result = new byte[ xml.getBytes().length ];
          ByteArrayInputStream in = new ByteArrayInputStream( out.toByteArray() );
          GZIPInputStream zipin = new GZIPInputStream( in );
          zipin.read( result );
          zipin.close();
          in.close();
          String xml2 = new String( result );
          System.out.println( "xml.equals( xml2 ): " + xml.equals( xml2 ) );
     public static void main( String[] args ) throws IOException {
          new CompressedStringTest();
}The length of the source and result strings are the same, but they are not equal. When I print out the lines which do not equal, I get this:
'</sysConfig>'
'</sxxxxxxxxx'where "x" are those small boxes, characters that can't be printed.
This is the source XML file I use:
<?xml version="1.0" encoding="UTF-8"?>
<sysConfig xid="0" version="0.1" id="1" xmlns:r2="http://....">
    <addresses class="java.util.ArrayList" xid="1">
        <address xid="2" id="1">
            <config xref="0"/>
            <addressType xid="3">NURSING_SERVICE</addressType>
            <externalId xid="4">0</externalId>
            <name xid="5">This is the name containing fourtyeight chars!!!</name>
            <street xid="6">street</street>
            <city xid="7">city</city>
            <zip xid="8">zip</zip>
            <telephone xid="9">12345</telephone>
            <fax xid="10">(123) 12345612345454597745</fax>
        </address>
     </addresses>
    <lastModified class="java.util.GregorianCalendar" xid="8167">2009-09-17 10:38:59.0 MESZ</lastModified>
    <customerNr xid="8168">FB-IK-01001</customerNr>
    <customerName xid="8169">A Customer</customerName>
    <logProtocolChanges>false</logProtocolChanges>
    <useHomeAsStartAddress>false</useHomeAsStartAddress>
    <sendMailEnabled>false</sendMailEnabled>
    <sendFaxEnabled>true</sendFaxEnabled>
</sysConfig>When I remove just one arbitrary line, the source and result strings do equal. This may have to do with some kind of buffer-length-problem, but I just can't figure out where the problem is.
I really appreciate your help
Thanks a lot!

Answer 1

The javadoc reads for "FilterInputStream.read(byte[] b)":I've read it. You're the one who needs to read it.
Reads up to* byte.length bytes of data from this input stream into an array of bytesSo I thought it just reads all available data.Why? That's not what it says, is it?
But when I print the return code of "read", it is not -1, meaning not the whole data has been read.If that is supposed to be 'meaning that the whole data has been read', you are mistaken. What was the return value? compared to the buffer length? You might find it interesting ...
I assume I just do not understand the read method completely.The return value is -1 for EOS, otherwise the number of bytes that were read. Just like it says in the Javadoc actually.
You have to use a loop, increment the offset, etc.