Message-ID: <3770054C.CCCC323B@crcg.edu>
Date: Tue, 22 Jun 1999 14:51:08 -0700
From: Steffen Zimmert <szimmert@crcg.edu>
Organization: Fraunhofer CRCG, Inc.
MIME-Version: 1.0
To: Peter Mount <petermount@it.maidstone.gov.uk>
CC: pgsql-interfaces@postgreSQL.org
Subject: Re: [INTERFACES] JDBC:Using Large Objects
References: 
 <1B3D5E532D18D311861A00600865478C9FCD@exchange1.nt.maidstone.gov.uk>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Hi,

> The large object code has been working for some time now, however not
> all of the stream methods work fully.
> 
> The best thing is to look at the blobtest and ImageViewer examples in
> the src/interfaces/jdbc/example directory, as they show what methods are
> currently supported.

I looked at the suggested source files and also compiled them. However,
I was not able to run neither Bobtest nor ImageViewer because the same
exception messages occured as in my own application. In addition, I
wrote also a little application based on the source of blobtest and the
exception occurs whenever I try to save a LargeObject. Here's the
source:

// Load the driver
Class.forName("postgresql.Driver");
    
// Connect to database
System.out.println("Connecting to Database URL = " + url);
db = DriverManager.getConnection(url, usr, pwd);
    
System.out.println("Connected...Now creating a statement");
stat = db.createStatement();

    
// Also, get the LargeObjectManager for this connection

System.out.println("Gaining access to LargeObjectApi.");
lom = ((postgresql.Connection)db).getLargeObjectAPI();
	
// Now create the large object

System.out.println("creating blob");

int oid = lom.create();

	  
System.out.println("Opening "+oid);

LargeObject blob = lom.open(oid);
	
// Create a new TestObject
System.out.println("Creating a new TestObject...");
TestObject tObject = new TestObject(1);
	
// Convert TestObject to Byte array
System.out.println("Converting object to byte array...");
byte[] objBytes = objectToBytes(tObject);
System.out.println("Size of byte array: " + objBytes.length);
	
// Writing byte array to blob
System.out.println("Writing byte array to blob...");
blob.write(objBytes,0,objBytes.length);
^^^^
The following exception occurs here!

Exception caught.
java.sql.SQLException: IOError while reading from backend:
java.io.IOException: The backend has broken the connection. Possibly the
action you have attempted has caused it to close.
java.sql.SQLException: IOError while reading from backend:
java.io.IOException: The backend has broken the connection. Possibly the
action you have attempted has caused it to close.
         at postgresql.PG_Stream.ReceiveChar(PG_Stream.java:183)
         at postgresql.fastpath.Fastpath.fastpath(Compiled Code)
         at postgresql.fastpath.Fastpath.fastpath(Fastpath.java:185)
         at
 postgresql.largeobject.LargeObject.write(LargeObject.java:147)
         at
 postgresql.PreparedStatement.setBytes(PreparedStatement.java:295)
         at basic.<init>(basic.java:45)
         at basic.main(basic.java:107)
 

Are there perhaps any parameters you have to specify during the
installation process of the database to explicitly allow the storage of
large objects?
Any help is welcome because I really don't know what to do now! :-((

-- 
Best Regards,
Steffen Zimmert


Steffen Zimmert
Fraunhofer Center for Research in Computer Graphics
Providence, Rhode Island, USA
email: szimmert@crcg.edu