HTTP post data from the Oracle database to another web server

Question

Hi ,
I have searched the forum and the net on this. And yes I have followed the links
http://awads.net/wp/2005/11/30/http-post-from-inside-oracle/
http://manib.wordpress.com/2007/12/03/utl_http/
and Eddie Awad's Blog on the same topic. I was successful in calling the servlet but I keep getting errors.
I am using Oracle 10 g and My servlet is part of a ADF BC JSF application.
My requirement is that I have blob table in another DB and our Oracle Forms application based on another DB has to view the documents . Viewing blobs over dblinks is not possible. So Option 1 is to call a procedure passing the doc_blob_id parameter and call the web server passing the parameters.
The errors I am getting is:
First the parameters passed returned null. and
2. Since my servlet directly downloads the document on the response outputStream, gives this error.
'com.evermind.server.http.HttpIOException: An established connection was aborted by the software in your host machine'
Any help please. I am running out of time.
Thanks

Answer 1

user10264958 wrote:
My requirement is that I have blob table in another DB and our Oracle Forms application based on another DB has to view the documents . Viewing blobs over dblinks is not possible. Incorrect. You can use remote LOBs via a database link. However, you cannot use a local LOB variable (called a LOB <i>locator</i>) to reference a remote LOB. A LOB variable/locator is a pointer - that pointer cannot reference a LOB that resides on a remote server. So simply do not use a LOB variable locally as it cannot reference a remote LOB.
Instead provide a remote interface that can deal with that LOB remotely, dereference that pointer on the remote system, and pass the actual contents being pointed at, to the local database.
The following demonstrates the basic approach. How one designs and implements the actual remote interface, need to be decided taking existing requirements into consideration. I simply used a very basic wrapper function.
SQL> --// we create a database link to our own database as it is easier for demonstration purposes
SQL> create database link remote_db connect to scott identified by tiger using
  2  '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=127.0.0.1)(PORT=1521))(CONNECT_DATA=(SID=dev)(SERVER=dedicated)))';
Database link created.
SQL> --// we create a table with a CLOB that we will access via this db link
SQL> create table xml_files( file_id number, xml_file clob );
Table created.
SQL> insert into xml_files values( 1, '<root><text>What do you want, universe?</text></root>' );
1 row created.
SQL> commit;
Commit complete.
SQL> --// a local select against the table works fine
SQL> select x.*, length(xml_file) as "SIZE" from xml_files x;
   FILE_ID XML_FILE                                                                                SIZE
         1 <root><text>What do you want, universe?</text></root>                                    53
SQL> --// a remote select against the table fails as we cannot use remote pointers/locators
SQL> select * from xml_files@remote_db x;
ERROR:
ORA-22992: cannot use LOB locators selected from remote tables
no rows selected
SQL> //-- we create an interface on the remote db to deal with the pointer for us
SQL> create or replace function ReturnXMLFile( fileID number, offset integer, amount integer ) return varchar2 is
  2          buffer  varchar2(32767);
  3  begin
  4          select
  5                  DBMS_LOB.SubStr( x.xml_file, amount, offset )
  6                          into
  7                  buffer
  8          from    xml_files x
  9          where   x.file_id = fileID;
10 
11          return( buffer );
12  end;
13  /
Function created.
SQL> --// we now can access the contents of the remote LOB (only in 4000 char chunks using this example)
SQL> select
  2          file_id,
  3          ReturnXMLFile@remote_db( x.file_id, 1, 4000 ) as "Chunk_1"
  4  from       xml_files@remote_db x;
   FILE_ID Chunk_1
         1 <root><text>What do you want, universe?</text></root>
SQL> --// we can also copy the entire remote LOB across into a local LOB and use the local one
SQL> declare
  2          c               clob;
  3          pos             integer;
  4          iterations      integer;
  5          buf             varchar2(20);   --// small buffer for demonstration purposes only
  6  begin
  7          DBMS_LOB.CreateTemporary( c, true );
  8 
  9          pos := 1;
10          iterations := 1;
11          loop
12                  buf := ReturnXMLFile@remote_db( 1, pos, 20 );
13                  exit when buf is null;
14                  pos := pos + length(buf);
15                  iterations := iterations + 1;
16                  DBMS_LOB.WriteAppend( c, length(buf), buf );
17          end loop;
18 
19          DBMS_OUTPUT.put_line( 'Copied '||length(c)||' byte(s) from remote LOB' );
20          DBMS_OUTPUT.put_line( 'Read Iterations: '||iterations );
21          DBMS_OUTPUT.put_line( 'LOB contents (1-4000):'|| DBMS_LOB.SubStr(c,4000,1) );
22 
23          DBMS_LOB.FreeTemporary( c );
24  end;
25  /
Copied 53 byte(s) from remote LOB
Read Iterations: 4
LOB contents (1-4000):<root><text>What do you want, universe?</text></root>
PL/SQL procedure successfully completed.
SQL> The concern is the size of the LOB. It does not always make sense to access the entire LOB in the database. What if that LOB is a 100GB in size? Irrespective of how you do it, selecting that LOB column from that table will require a 100GB of data to be transferred from the database to your client.
So you need to decide WHY you want the LOB on the client (which will be the local PL/SQL code in case of dealing with a LOB on a remote database)? Do you need the entire LOB? Do you need a specific piece from it? Do you need the database to first parse that LOB into a more structured data struct and then pass specific information from that struct to you? Etc.
The bottom line however is that you can use remote LOBs. Simply that you cannot use a local pointer variable to point and dereference a remote LOB.