For example, suppose you have a table containing the file names of images and you also want to store the image in a bytea column:
CREATE TABLE images (imgname text, img bytea);
To insert an image, you would use:
File file = new File("myimage.gif");
FileInputStream fis = new FileInputStream(file);
PreparedStatement ps = conn.prepareStatement("INSERT INTO images VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setBinaryStream(2, fis, (int)file.length());
ps.executeUpdate();
ps.close();
fis.close();
Here,
setBinaryStream() transfers a set number of bytes from a stream into the column of type
bytea. This also could have been done using the
setBytes() method if the contents of the image was already in a
byte[].
Note
The length parameter to setBinaryStream must be correct. There is no way to indicate that the stream is of unknown length. If you are in this situation, you must read the stream yourself into temporary storage and determine the length. Now with the correct length you may send the data from temporary storage on to the driver.
Retrieving an image is even easier. (We use PreparedStatement here, but the Statement class can equally be used.)
PreparedStatement ps = conn.prepareStatement("SELECT img FROM images WHERE imgname = ?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
byte[] imgBytes = rs.getBytes(1);
// use the data in some way here
}
rs.close();
ps.close();
Here the binary data was retrieved as an byte[]. You could have used a InputStream object instead.
Alternatively you could be storing a very large file and want to use the LargeObject API to store the file:
CREATE TABLE imageslo (imgname text, imgoid oid);
To insert an image, you would use:
// All LargeObject API calls must be within a transaction block
conn.setAutoCommit(false);
// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();
// Create a new large object
long oid = lobj.createLO(LargeObjectManager.READ | LargeObjectManager.WRITE);
// Open the large object for writing
LargeObject obj = lobj.open(oid, LargeObjectManager.WRITE);
// Now open the file
File file = new File("myimage.gif");
FileInputStream fis = new FileInputStream(file);
// Copy the data from the file to the large object
byte buf[] = new byte[2048];
int s, tl = 0;
while ((s = fis.read(buf, 0, 2048)) > 0) {
obj.write(buf, 0, s);
tl += s;
}
// Close the large object
obj.close();
// Now insert the row into imageslo
PreparedStatement ps = conn.prepareStatement("INSERT INTO imageslo VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setLong(2, oid);
ps.executeUpdate();
ps.close();
fis.close();
// Finally, commit the transaction.
conn.commit();
Retrieving the image from the Large Object:
// All LargeObject API calls must be within a transaction block
conn.setAutoCommit(false);
// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();
PreparedStatement ps = conn.prepareStatement("SELECT imgoid FROM imageslo WHERE imgname = ?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
// Open the large object for reading
long oid = rs.getLong(1);
LargeObject obj = lobj.open(oid, LargeObjectManager.READ);
// Read the data
byte buf[] = new byte[obj.size()];
obj.read(buf, 0, obj.size());
// Do something with the data read here
// Close the object
obj.close();
}
rs.close();
ps.close();
// Finally, commit the transaction.
conn.commit();
