How to write blob into OS file ?

1. create a database directory :
create or replace database directory image_test_dir
as 'd:\db_dir\'

2. use dbms_lob and utl_file package to read data chunk wise.

declare
    v_offset        number  := 1;
    v_buffer_size   number  := 1000;
    v_file_handle   UTL_FILE.FILE_TYPE;
    v_src_lob       blob;
    v_len           integer;
    v_buffer          raw(1000);

begin
    /*select image_front into v_src_lob
    from inward_image where rownum=1;*/
    
    select img into v_src_lob
    from image_upload where rownum=1;
    
    v_len   := DBMS_LOB.GETLENGTH(v_src_lob);
    
    v_file_handle := UTL_FILE.FOPEN('IMAGE_TEST_DIR', 'f.pdf', 'wb');
    
    while v_offset < v_Len
    loop
        
        DBMS_LOB.READ(v_src_lob, v_buffer_size, v_offset, v_buffer );
        
        UTL_FILE.PUT_RAW(v_file_handle, v_buffer);
        
        --DBMS_OUTPUT.PUT_LINE( v_offset || '                '  ||  v_buffer_size );
        
        v_offset := v_offset + v_buffer_size;
        
    
    end loop;
    
    
    --DBMS_OUTPUT.PUT_LINE();
    
    UTL_FILE.FFLUSH(v_file_handle);
    
    UTL_FILE.FCLOSE(v_file_handle);
    
    
end;