Subject: [Pljava-dev] How to read LargeObject with pljava?

From: olegvvasylenko at gmail.com (Oleg Vasylenko)
Date: Sat, 13 Jun 2009 12:43:17 +0300

Hi everybody!

Have some code to read LargeObject from db and create digest message for 
the it content. The code generate an error attemtting to read a portion 
of LO.

Could anybody give an example how to read LO from database?

I'm using jre1.6.0.13, pljava1.4.0, postgresql8.3.7.

Thanks.

import java.io.FileOutputStream;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.logging.Logger;
import org.postgresql.largeobject.LargeObject;
import org.postgresql.largeobject.LargeObjectManager;

public class ServerDigestCreator {

public static String 
anotherCreateStrDigest(org.postgresql.pljava.internal.Oid lObjectId) 
throws  SQLException,NoSuchAlgorithmException
   {
       String digest = null;
       java.sql.Savepoint sp = null;
       if(lObjectId==null) return null;
       java.sql.Connection aConnection = 
DriverManager.getConnection("jdbc:default:connection");
       try{
             sp = aConnection.setSavepoint();
       org.postgresql.pljava.internal.LargeObject lo =  
org.postgresql.pljava.internal.LargeObject.open(lObjectId, 
org.postgresql.pljava.internal.LargeObject.INV_READ);
                 MessageDigest aDigest = MessageDigest.getInstance("md5");
             if(lo==null)       {
               aConnection.releaseSavepoint(sp);
               return digest;
       }
       byte buf[] = new byte[2048];
       int s=0;
         while((s = lo.read(buf))!=0)              
<---------------------- Error occurs here 
=============================================================
               aDigest.update(buf);               byte[] digestByteArray 
= aDigest.digest();
       BigInteger tempBI = new BigInteger(digestByteArray);
       digest = tempBI.toString();             lo.close();
         aConnection.releaseSavepoint(sp);
       }
       catch(SQLException ex)
       {              if(sp!=null)
               aConnection.rollback(sp);
           Logger.getAnonymousLogger().info("ERROR: " + ex.getMessage() 
+ "\n");
           throw new SQLException(ex.getMessage());
       }
             return digest;
   }

---

From: olegvvasylenko at gmail.com (Oleg Vasylenko)
Date: Wed, 17 Jun 2009 16:12:49 +0300

Does org.postgresql.pljava.internal.LargeObject object and methods 
read/write/open/close still being experimental or methods have to work 
correctly in PLJava 1.4.0?

---

From: books at ejurka.com (Kris Jurka)
Date: Thu, 18 Jun 2009 13:52:14 -0400 (EDT)

> correctly in PLJava 1.4.0?

Looking at the source code, it doesn't work at all.  With the attached 
patch it mostly works.  LargeObject.create still doesn't work and you will 
get warnings about relcache reference leaks, but these are harmless and 
can be ignored.

Kris Jurka
-------------- next part --------------
Index: src/C/pljava/type/LargeObject.c
===================================================================
RCS file: /cvsroot/pljava/org.postgresql.pljava/src/C/pljava/type/LargeObject.c,v
retrieving revision 1.14
diff -c -r1.14 LargeObject.c
*** src/C/pljava/type/LargeObject.c	28 May 2006 22:01:48 -0000	1.14
--- src/C/pljava/type/LargeObject.c	18 Jun 2009 17:07:49 -0000
***************
*** 23,38 ****
   */
  jobject LargeObject_create(LargeObjectDesc* lo)
  {
- 	jobject jlo;
- 	Ptr2Long loH;
- 
  	if(lo == 0)
  		return 0;
  
! 	loH.longVal = 0L; /* ensure that the rest is zeroed out */
! 	loH.ptrVal = lo;
! 	jlo = JNI_newObject(s_LargeObject_class, s_LargeObject_init, loH.longVal);
! 	return jlo;
  }
  
  extern void LargeObject_initialize(void);
--- 23,32 ----
   */
  jobject LargeObject_create(LargeObjectDesc* lo)
  {
  	if(lo == 0)
  		return 0;
  
! 	return JNI_newObject(s_LargeObject_class, s_LargeObject_init, Invocation_createLocalWrapper(lo));
  }
  
  extern void LargeObject_initialize(void);