How to load BLOB in the database?

I have been asked yesterday how to read and write blobs in the database.

With java :
read from an input stream

InputStream myBlobInputStream = 
  connection . 
    createStatement() . 
      executeQuery("select myBlob from t") . 
        getBlob(1) . 
          getBinaryStream();

write to an output stream

OutputStream myBlobStream = 
  connection .
    createStatement() .
      executeQuery("select myBlob from t for update") . 
        getBlob(1) . 
          getBinaryOutputStream();

where connection is your java.sql.connection.

You could also use PL/SQL and the DBMS_LOB API. There is a complete book (306 pages!) in the doc about working with large objects : Application Developer’s Guide – Large Objects.

Sometimes, you can use plain SQL.

SQL> create table t(x BLOB);
Table created

SQL> insert into t values(utl_raw.cast_from_number(1));
1 row inserted

SQL> select utl_raw.cast_to_number(x) from t;
UTL_RAW.CAST_TO_NUMBER(X)
-------------------------
                        1

A smart move may be to use SQL Loader. You can specify one file per row

LOAD DATA INFILE '/tmp/x.txt' INTO TABLE "T"
(name filler char(255), x lobfile(name) terminated by EOF)

and your import file /tmp/x.txt will look like

x.gif
y.gif

but you could also load a 10000 long characters column from your input file in a CLOB column, just by specifying VARCHARC(4,10000) as a datatype

6 thoughts on “How to load BLOB in the database?”

  1. Laurent,

    Also a temporary BLOB can be created when using java:


    BLOB myBlob = BLOB.createTemporary(connection, false, BLOB.DURATION_SESSION);

    This might come in handy not to create a record with an empty blob first.

    Regards,

    Remco

  2. How about using PL/SQL to load Multimedia LOBs delivered from the web? I have an application that is doing this, and it is working just fine, but requires a commit after EACH file being loaded (because of the SELECT…FOR UPDATE). Fine for a single-user environment – sometimes OK for a 5 user environment – but once I have 100 users uploading files at the same time the COMMITs go through the roof and obviously the frequent commits are not best practice.

    I’ve tried SQL*Loader but it’s not consistent enough in such a dynamic environment. PL/SQL is more consistently accurate, but slow as death.

    Any suggestions? Or is this a “c’est la vie” situation.

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