* It's only if you use the non jdbc facilities, do you have to take this into
* account.
*
+ * Note: For PostgreSQL 6.4, the driver is now Thread safe, so this example
+ * application has been updated to use multiple threads, especially in the
+ * image storing and retrieving methods.
*/
public class ImageViewer implements ItemListener
// This is a simple component to display our image
public class imageCanvas extends Canvas
{
+ // holds the image
private Image image;
+ // holds the background buffer
+ private Image bkg;
+
+ // the size of the buffer
+ private Dimension size;
+
public imageCanvas()
{
image=null;
paint(g);
}
- public void paint(Graphics g)
+ /**
+ * Paints the image, using double buffering to prevent screen flicker
+ */
+ public void paint(Graphics gr)
{
+ Dimension s = getSize();
+
+ if(size==null || bkg==null || !s.equals(size)) {
+ size = s;
+ bkg = createImage(size.width,size.height);
+ }
+
+ // now set the background
+ Graphics g = bkg.getGraphics();
g.setColor(Color.gray);
- g.fillRect(0,0,getSize().width,getSize().height);
+ g.fillRect(0,0,s.width,s.height);
+ // now paint the image over the background
if(image!=null)
g.drawImage(image,0,0,this);
+
+ // dispose the graphics instance
+ g.dispose();
+
+ // paint the image onto the component
+ gr.drawImage(bkg,0,0,this);
+
}
+
}
public ImageViewer(Frame f,String url,String user,String password) throws ClassNotFoundException, FileNotFoundException, IOException, SQLException
}
/**
- * This imports an image into the database.
- *
- * This is the most efficient method, using the large object extension.
+ * This imports an image into the database, using a Thread to do this in the
+ * background.
*/
public void importImage()
{
String dir = d.getDirectory();
d.dispose();
- // Now the real import stuff
- if(name!=null && dir!=null) {
- try {
- System.out.println("Importing file");
- // A temporary buffer - this can be as large as you like
- byte buf[] = new byte[2048];
-
- // Open the file
- System.out.println("Opening file "+dir+"/"+name);
- FileInputStream fis = new FileInputStream(new File(dir,name));
-
- // Gain access to large objects
- System.out.println("Gaining LOAPI");
-
- // Now create the large object
- System.out.println("creating blob");
- int oid = lom.create();
-
- System.out.println("Opening "+oid);
- LargeObject blob = lom.open(oid);
+ // now start the true importer
+ Thread t = new importer(db,name,dir);
+ //t.setPriority(Thread.MAX_PRIORITY);
+ t.start();
+ }
+
+ /**
+ * This is an example of using a thread to import a file into a Large Object.
+ * It uses the Large Object extension, to write blocks of the file to the
+ * database.
+ */
+ class importer extends Thread
+ {
+ String name,dir;
+ Connection db;
+
+ public importer(Connection db,String name,String dir) {
+ this.db = db;
+ this.name = name;
+ this.dir = dir;
+ }
+
+ public void run() {
+
+ // Now the real import stuff
+ if(name!=null && dir!=null) {
+ Statement stat = null;
- // Now copy the file into the object.
- //
- // Note: we dont use write(buf), as the last block is rarely the same
- // size as our buffer, so we have to use the amount read.
- System.out.println("Importing file");
- int s,t=0;
- while((s=fis.read(buf,0,buf.length))>0) {
- System.out.println("Block s="+s+" t="+t);t+=s;
- blob.write(buf,0,s);
+ try {
+ // fetch the large object manager
+ LargeObjectManager lom = ((postgresql.Connection)db).getLargeObjectAPI();
+
+ System.out.println("Importing file");
+ // A temporary buffer - this can be as large as you like
+ byte buf[] = new byte[2048];
+
+ // Open the file
+ System.out.println("Opening file "+dir+"/"+name);
+ FileInputStream fis = new FileInputStream(new File(dir,name));
+
+ // Gain access to large objects
+ System.out.println("Gaining LOAPI");
+
+ // Now create the large object
+ System.out.println("creating blob");
+ int oid = lom.create();
+
+ System.out.println("Opening "+oid);
+ LargeObject blob = lom.open(oid);
+
+ // Now copy the file into the object.
+ //
+ // Note: we dont use write(buf), as the last block is rarely the same
+ // size as our buffer, so we have to use the amount read.
+ System.out.println("Importing file");
+ int s,t=0;
+ while((s=fis.read(buf,0,buf.length))>0) {
+ System.out.println("Block s="+s+" t="+t);t+=s;
+ blob.write(buf,0,s);
+ }
+
+ // Close the object
+ System.out.println("Closing blob");
+ blob.close();
+
+ // Now store the entry into the table
+
+ // As we are a different thread to the other window, we must use
+ // our own thread
+ stat = db.createStatement();
+ stat.executeUpdate("insert into images values ('"+name+"',"+oid+")");
+
+ // Finally refresh the names list, and display the current image
+ ImageViewer.this.refreshList();
+ ImageViewer.this.displayImage(name);
+ } catch(Exception ex) {
+ label.setText(ex.toString());
+ } finally {
+ // ensure the statement is closed after us
+ try {
+ if(stat != null)
+ stat.close();
+ } catch(SQLException se) {
+ System.err.println("closing of Statement failed");
+ }
}
-
- // Close the object
- System.out.println("Closing blob");
- blob.close();
-
- // Now store the entry into the table
- stat.executeUpdate("insert into images values ('"+name+"',"+oid+")");
- stat.close();
-
- // Finally refresh the names list, and display the current image
- refreshList();
- displayImage(name);
- } catch(Exception ex) {
- label.setText(ex.toString());
}
}
}
}
try {
- Frame frame = new Frame("PostgreSQL ImageViewer v6.3 rev 1");
+ Frame frame = new Frame("PostgreSQL ImageViewer v6.4 rev 1");
frame.setLayout(new BorderLayout());
ImageViewer viewer = new ImageViewer(frame,args[0],args[1],args[2]);
frame.pack();
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