[Sanselan] Writing exif metadata to jpeg

[unixhead]

Hello :)
I want to edit GPS tag and save new GPS latitude and longitude to jpeg. Ok I found a Sanselan Java library which lets to do this. There is an example how to write metadata org.apache.sanselan.sampleUsage.WriteExifMetadataE xample Source Code | www.massapi.com end I used this part

package test1.gpstest1;

import java.io.BufferedOutputStream;
import java.io.File;
//import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.sanselan.ImageReadException;
import org.apache.sanselan.ImageWriteException;
import org.apache.sanselan.Sanselan;
import org.apache.sanselan.common.IImageMetadata;
import org.apache.sanselan.formats.jpeg.JpegImageMetadata;
import org.apache.sanselan.formats.jpeg.exifRewrite.ExifRewriter;
import org.apache.sanselan.formats.tiff.TiffImageMetadata;
import org.apache.sanselan.formats.tiff.constants.TiffConstants;
import org.apache.sanselan.formats.tiff.write.TiffOutputDirectory;
import org.apache.sanselan.formats.tiff.write.TiffOutputField;
import org.apache.sanselan.formats.tiff.write.TiffOutputSet;
//import org.apache.sanselan.util.IOUtils;

public class Testgps
{

/**
	 * This example illustrates how to add/update EXIF metadata in a JPEG file.
	 * 
	 * @param jpegImageFile
	 *            A source image file.
	 * @param dst
	 *            The output file.
	 * @throws IOException
	 * @throws ImageReadException
	 * @throws ImageWriteException
	 */
	public void changeExifMetadata(File jpegImageFile, File dst)
			throws IOException, ImageReadException, ImageWriteException
	{
		OutputStream os = null;
		try
		{
			TiffOutputSet outputSet = null;

			// note that metadata might be null if no metadata is found.
			IImageMetadata metadata = Sanselan.getMetadata(jpegImageFile);
			JpegImageMetadata jpegMetadata = (JpegImageMetadata) metadata;
			if (null != jpegMetadata)
			{
				// note that exif might be null if no Exif metadata is found.
				TiffImageMetadata exif = jpegMetadata.getExif();

				if (null != exif)
				{
					// TiffImageMetadata class is immutable (read-only).
					// TiffOutputSet class represents the Exif data to write.
					//
					// Usually, we want to update existing Exif metadata by
					// changing
					// the values of a few fields, or adding a field.
					// In these cases, it is easiest to use getOutputSet() to
					// start with a "copy" of the fields read from the image.
					outputSet = exif.getOutputSet();
				}
			}

			// if file does not contain any exif metadata, we create an empty
			// set of exif metadata. Otherwise, we keep all of the other
			// existing tags.
			if (null == outputSet)
				outputSet = new TiffOutputSet();

			{
				// Example of how to add a field/tag to the output set.
				//
				// Note that you should first remove the field/tag if it already
				// exists in this directory, or you may end up with duplicate
				// tags. See above.
				//
				// Certain fields/tags are expected in certain Exif directories;
				// Others can occur in more than one directory (and often have a
				// different meaning in different directories).
				//
				// TagInfo constants often contain a description of what
				// directories are associated with a given tag.
				//
				// see
				// org.apache.sanselan.formats.tiff.constants.AllTagConstants
				//
				TiffOutputField aperture = TiffOutputField.create(
						TiffConstants.EXIF_TAG_APERTURE_VALUE,
						outputSet.byteOrder, new Double(0.3));
				TiffOutputDirectory exifDirectory = outputSet
						.getOrCreateExifDirectory();
				// make sure to remove old value if present (this method will
				// not fail if the tag does not exist).
				exifDirectory.removeField(TiffConstants.EXIF_TAG_APERTURE_VALUE);
				exifDirectory.add(aperture);
			}

			{
				// Example of how to add/update GPS info to output set.

				// New York City
				double longitude = -74.0; // 74 degrees W (in Degrees East)
				double latitude = 40 + 43 / 60.0; // 40 degrees N (in Degrees
				// North)

				outputSet.setGPSInDegrees(longitude, latitude);
			}

			// printTagValue(jpegMetadata, TiffConstants.TIFF_TAG_DATE_TIME);

			//os = new FileOutputStream(dst);
			os = new BufferedOutputStream(os);

			new ExifRewriter().updateExifMetadataLossless(jpegImageFile, os,
					outputSet);

			os.close();
			os = null;
		} finally
		{
			if (os != null)
				try
				{
					os.close();
				} catch (IOException e)
				{

				}
		}
	}
public static void main(String [] args) throws ImageReadException, 
					                    ImageWriteException, 
								       IOException {
		File jpegImageFile = new File("test22.JPG");
		//String jpegImageFile ="P1020220.JPG";
		File dst = new File("test23.JPG");
	     new Testgps().changeExifMetadata(jpegImageFile, dst);
	     System.out.println("Data has been changed successfull!");
	   }

}

ok it works but this example creates a new photo with new gps latitude/longitude. I would like to set new gps values on the same photo, how I can do this ? Generally I want to create application similar to Picasa (photo viewer + google maps) .. and in this case when I drag and drop marker on map I want to save new gps exif metadata to photo.. so according with this example it will be create new photo every time? stupid ...I have a little experience with Java .. any sygestion/example is very usefull for me :)