注：下列过程中的参数p_filename为外部文件名称，p_name用于标识唯一的一行

1.创建目录utl_dir用于文件的导入、导出
create or replace directory utl_dir as 'd:\';

2.给所有用户赋予读写utl_dir的权限
grant write,read on directory utl_dir to public;

3.创建测试表blob_test，其中列a为blob类型，b列在实际应用中可以是表的PK列
create table blob_test(a blob,b number);

4.将外部文件插入blob列
CREATE OR REPLACE PROCEDURE insert_blob(p_name varchar2,p_filename varchar2) IS
  i_blob BLOB;
  i_file BFILE := BFILENAME('UTL_DIR',p_filename);
BEGIN
  INSERT INTO blob_test VALUES (EMPTY_BLOB(),p_name)
  RETURNING test INTO i_blob;

  DBMS_LOB.FILEOPEN(i_file);
  DBMS_LOB.LOADFROMFILE(i_blob, i_file, DBMS_LOB.GETLENGTH(i_file));
  DBMS_LOB.FILECLOSE(i_file);

  COMMIT;
END;

5.用外部文件更新blob列
CREATE OR REPLACE PROCEDURE update_blob(p_name varchar2,p_filename varchar2) IS
  i_blob BLOB;
  i_file BFILE := BFILENAME('UTL_DIR',p_filename);
BEGIN
  UPDATE blob_test SET test = EMPTY_BLOB() WHERE b = p_name
  RETURNING test INTO i_blob;

  DBMS_LOB.FILEOPEN(i_file);
  DBMS_LOB.LOADFROMFILE(i_blob, i_file, DBMS_LOB.GETLENGTH(i_file));
  DBMS_LOB.FILECLOSE(i_file);

  COMMIT;
END;

6.用于查看insert、update是否成功的语句
SELECT DBMS_LOB.GETLENGTH(test) FROM blob_test;

7.将数据库中的blob列导出为外部文件
CREATE OR REPLACE PROCEDURE dump_blob (p_name varchar2,p_filename varchar2) IS
  l_file      UTL_FILE.FILE_TYPE;
  l_buffer    RAW(32767);
  l_amount    BINARY_INTEGER := 32767;
  l_pos       INTEGER := 1;
  l_blob      BLOB;
  l_blob_len  INTEGER;
BEGIN
  SELECT test INTO l_blob FROM blob_test WHERE b = p_name;

  l_blob_len := DBMS_LOB.GETLENGTH(l_blob);
  l_file := UTL_FILE.FOPEN('UTL_DIR',p_filename,'wb', 32767);

  WHILE l_pos < l_blob_len LOOP
    DBMS_LOB.READ (l_blob, l_amount, l_pos, l_buffer);
    UTL_FILE.PUT_RAW(l_file, l_buffer, TRUE);
    l_pos := l_pos + l_amount;
  END LOOP;

  UTL_FILE.FCLOSE(l_file);

EXCEPTION
  WHEN OTHERS THEN
    IF UTL_FILE.IS_OPEN(l_file) THEN
      UTL_FILE.FCLOSE(l_file);
    END IF;
    RAISE;
END;