How to Convert a BufferedInputStream from a Database to a BufferedImage?

Converting BufferedInputStream to an Image

Problem:

How can I convert a BufferedInputStream object, retrieved from a database, into a BufferedImage? The existing code returns a null image.

Solution:

1. Verify that the BufferedInputStream contains a valid image. Save it to a file and then read it back as a BufferedImage to confirm.
2. Ensure that the correct length of the Blob is used when getting the bytes. For H2 database, the length is returned as a long, but Blob#getBytes expects an int.
3. Alternatively, use Blob#getBinaryStream instead of Blob#getBytes. This may be necessary if the database does not store Blob contents in memory.

Example:

The following Java code uses Blob#getBinaryStream to read an image from the database and convert it to a BufferedImage:

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.imageio.ImageIO;

public class ImageDatabaseHelper {

    private Connection con;

    public BufferedImage loadImage(int imageId) throws IOException, SQLException {

        PreparedStatement stmt = null;
        ResultSet rs = null;
        BufferedImage image = null;

        try {

            stmt = con.prepareStatement("select image from images where id = ?");
            stmt.setInt(1, imageId);
            rs = stmt.executeQuery();

            while (rs.next()) {

                Blob blob = rs.getBlob(1);
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                try (ByteArrayInputStream bais = new ByteArrayInputStream(blob.getBinaryStream())) {
                    ImageIO.read(bais).writeTo(baos);
                }
                image = ImageIO.read(new ByteArrayInputStream(baos.toByteArray()));
            }

        } finally {
            try {
                rs.close();
            } catch (Exception e) {
            }
            try {
                stmt.close();
            } catch (Exception e) {
            }
        }

        return image;
    }

}

The above is the detailed content of How to Convert a BufferedInputStream from a Database to a BufferedImage?. For more information, please follow other related articles on the PHP Chinese website!