PNGException "crc corruption" when attempting to create ImageIcon objects from ZIP archive

Question

I've got a ZIP file containing a number of PNG images that I am trying to load into my Java application as ImageIcon resources directly from the archive. Here's my code:

import java.io.*;
import java.util.Enumeration;
import java.util.zip.*;
import javax.swing.ImageIcon;

public class Test {
  public static void main( String[] args )
  {
    if( args.length == 0 )
    {
      System.out.println("usage: java Test.java file.zip");
      return;
    }
    File archive = new File( args[0] );
    if( !archive.exists() || !archive.canRead() )
    {
      System.err.printf("Unable to find/access %s.\n", archive);
      return;
    }

    try {
      ZipFile zip = new ZipFile(archive);
      Enumeration <? extends ZipEntry>e = zip.entries();
      while( e.hasMoreElements() )
      {
        ZipEntry entry = (ZipEntry) e.nextElement();
        int size = (int) entry.getSize();
        int count = (size % 1024 == 0) ? size / 1024 : (size / 1024)+1;
        int offset = 0;
        int nread, toRead;

        byte[] buffer = new byte[size];
        for( int i = 0; i < count; i++ )
        {
          offset = 1024*i;
          toRead = (size-offset > 1024) ? 1024 : size-offset;
          nread = zip.getInputStream(entry).read(buffer, offset, toRead);
        }
        ImageIcon icon = new ImageIcon(buffer); // boom -- why?
      }
      zip.close();      
    } catch( IOException ex ) {
      System.err.println(ex.getMessage());
    }
  }
}

The sizes reported by entry.getSize() match the uncompressed size of the PNG files, and I am able to read the data out of the archive without any exceptions, but the creation of the ImageIcon blows up. The stacktrace:

sun.awt.image.PNGImageDecoder$PNGException: crc corruption
 at sun.awt.image.PNGImageDecoder.getChunk(PNGImageDecoder.java:699)
 at sun.awt.image.PNGImageDecoder.getData(PNGImageDecoder.java:707)
 at sun.awt.image.PNGImageDecoder.produceImage(PNGImageDecoder.java:234)
 at sun.awt.image.InputStreamImageSource.doFetch(InputStreamImageSource.java:246)
 at sun.awt.image.ImageFetcher.fetchloop(ImageFetcher.java:172)
 at sun.awt.image.ImageFetcher.run(ImageFetcher.java:136)
sun.awt.image.PNGImageDecoder$PNGException: crc corruption
 at sun.awt.image.PNGImageDecoder.getChunk(PNGImageDecoder.java:699)
 at sun.awt.image.PNGImageDecoder.getData(PNGImageDecoder.java:707)
 at sun.awt.image.PNGImageDecoder.produceImage(PNGImageDecoder.java:234)
 at sun.awt.image.InputStreamImageSource.doFetch(InputStreamImageSource.java:246)
 at sun.awt.image.ImageFetcher.fetchloop(ImageFetcher.java:172)
 at sun.awt.image.ImageFetcher.run(ImageFetcher.java:136)

Can anyone shed some light on it? Google hasn't turned up any useful information.

Answer 1

You might must pull getInputStream() out of the inner loop, instead of invoking it repeatedly for each block.