How convert CLOB to BLOB in Oracle?

Question

Firstly I converted a BLOB of an image to CLOB, and then converted that CLOB back to BLOB. I cannot see the reconverted image. How can i solve this problem?

blob_to_clob function:

CREATE OR REPLACE FUNCTION blob_to_clob (blob_in IN BLOB) RETURN CLOB AS
  v_clob CLOB;
  v_varchar VARCHAR2(32767);
  v_start PLS_INTEGER := 1;
  v_buffer PLS_INTEGER := 32767;
BEGIN
  DBMS_LOB.CREATETEMPORARY(v_clob, TRUE);
  FOR i IN 1..CEIL(DBMS_LOB.GETLENGTH(blob_in) / v_buffer)
  LOOP
    v_varchar := UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(blob_in, v_buffer, v_start));
    DBMS_LOB.WRITEAPPEND(v_clob, LENGTH(v_varchar), v_varchar);
    v_start := v_start + v_buffer;
  END LOOP;
  RETURN v_clob;
END blob_to_clob;

clob_to_blob function:

CREATE OR REPLACE FUNCTION clob_to_blob2(p_clob IN CLOB) RETURN BLOB IS
  v_blob BLOB;
  v_offset NUMBER DEFAULT 1;
  v_amount NUMBER DEFAULT 4096;
  v_offsetwrite NUMBER DEFAULT 1;
  v_amountwrite NUMBER;
  v_buffer VARCHAR2(4096 CHAR);
BEGIN dbms_lob.createtemporary(v_blob, TRUE);
  Begin
    LOOP
      dbms_lob.READ (lob_loc => p_clob,
        amount  => v_amount,
        offset  => v_offset,
        buffer  => v_buffer);

      v_amountwrite := utl_raw.length (r => utl_raw.cast_to_raw(c => v_buffer));

      dbms_lob.WRITE (lob_loc => v_blob,
        amount  => v_amountwrite,
        offset  => v_offsetwrite,
        buffer  => utl_raw.cast_to_raw(v_buffer));

      v_offsetwrite := v_offsetwrite + v_amountwrite;

      v_offset := v_offset + v_amount;
      v_amount := 4096;
    END LOOP;
  EXCEPTION
    WHEN no_data_found THEN
    NULL;
  End;
  RETURN v_blob;
END clob_to_blob2;

Answer 1

Code like this will perform minimal recoding:

create or replace function clob2blob(AClob CLOB) return BLOB is
  Result BLOB;
  o1 integer;
  o2 integer;
  c integer;
  w integer;
begin
  o1 := 1;
  o2 := 1;
  c := 0;
  w := 0;
  DBMS_LOB.CreateTemporary(Result, true);
  DBMS_LOB.ConvertToBlob(Result, AClob, length(AClob), o1, o2, 0, c, w);
  return(Result);
end clob2blob;
/

But CLOB can not properly contain all Image data without any encoding like Base64

Answer 2

You can use:

CREATE FUNCTION clob_to_blob(
  value            IN CLOB,
  charset_id       IN INTEGER DEFAULT DBMS_LOB.DEFAULT_CSID,
  error_on_warning IN NUMBER  DEFAULT 0
) RETURN BLOB
IS
  result       BLOB;
  dest_offset  INTEGER := 1;
  src_offset   INTEGER := 1;
  lang_context INTEGER := DBMS_LOB.DEFAULT_LANG_CTX;
  warning      INTEGER;
  warning_msg  VARCHAR2(50);
BEGIN
  DBMS_LOB.CreateTemporary(
    lob_loc => result,
    cache   => TRUE
  );

  DBMS_LOB.CONVERTTOBLOB(
    dest_lob     => result,
    src_clob     => value,
    amount       => LENGTH( value ),
    dest_offset  => dest_offset,
    src_offset   => src_offset,
    blob_csid    => charset_id,
    lang_context => lang_context,
    warning      => warning
  );
  
  IF warning != DBMS_LOB.NO_WARNING THEN
    IF warning = DBMS_LOB.WARN_INCONVERTIBLE_CHAR THEN
      warning_msg := 'Warning: Inconvertible character.';
    ELSE
      warning_msg := 'Warning: (' || warning || ') during CLOB conversion.';
    END IF;
    
    IF error_on_warning = 0 THEN
      DBMS_OUTPUT.PUT_LINE( warning_msg );
    ELSE
      RAISE_APPLICATION_ERROR(
        -20567, -- random value between -20000 and -20999
        warning_msg
      );
    END IF;
  END IF;

  RETURN result;
END clob_to_blob;
/