CREATE TABLE TEST.T_IMG
(
    IDN       VARCHAR2(18 BYTE)      NOT NULL,IMG       BLOB                   NOT NULL,IMGHASH   VARCHAR2(128 BYTE)
);

字符串和blob的SHA256哈希值由以下代码计算,该代码基于Sean Stuber在http://seanstuber.wordpress.com/2012/03/22/using-java-to-extend-dbms_crypto/的示例

CREATE OR REPLACE AND RESOLVE JAVA SOURCE NAMED sha2 AS
import java.security.MessageDigest;
import oracle.sql.*;
public class sha2
{
    public static oracle.sql.RAW get_digest_string( String p_string,int p_bits ) throws Exception
    {
        MessageDigest v_md = MessageDigest.getInstance( "SHA-" + p_bits );
        byte[] v_digest;
        v_digest = v_md.digest( p_string.getBytes( "UTF-8" ) );
        return RAW.newRAW(v_digest);
    }

    public static oracle.sql.RAW get_digest_blob( oracle.sql.BLOB p_blob,int p_bits ) throws Exception
    {
        byte[] allBytesInBlob;
        allBytesInBlob = p_blob.getBytes(1,(int) p_blob.length());
        MessageDigest v_md = MessageDigest.getInstance( "SHA-" + p_bits );
        byte[] v_digest = v_md.digest( allBytesInBlob );
        return RAW.newRAW(v_digest);
    }
}
/
CREATE OR REPLACE FUNCTION sha2_string(p_string in VARCHAR2,p_bits in number)
RETURN RAW AS LANGUAGE JAVA
NAME 'sha2.get_digest_string( java.lang.String,int ) return oracle.sql.RAW';
/
CREATE OR REPLACE FUNCTION sha2_blob(p_byte in BLOB,p_bits in number)
RETURN RAW AS LANGUAGE JAVA
NAME 'sha2.get_digest_blob( oracle.sql.BLOB,int ) return oracle.sql.RAW';
/

以上功能有效.测试他我得到：

SELECT sha2_string('0123456789',256) FROM DUAL;
SELECT sha2_blob(utl_raw.cast_to_raw('0123456789'),256) FROM DUAL;

SHA2_STRING(‘0123456789’,256)
——————————————————————————– 84D89877F0D4041EFB6BF91A16F0248F2FD573E6AF05C19F96BEDB9F882F7882
1 row selected.

SHA2_BLOB(UTL_RAW.CAST_TO_RAW(‘0123456789’),256)
——————————————————————————– 84D89877F0D4041EFB6BF91A16F0248F2FD573E6AF05C19F96BEDB9F882F7882
1 row selected.

我在T_IMG上插入或更新时使用before触发器来计算图像列的SH256散列.

CREATE OR REPLACE TRIGGER TEST.TR_IMG_UPSERT
BEFORE INSERT OR UPDATE
ON TEST.T_IMG

FOR EACH ROW
DECLARE 
    imghash varchar2(128);
    vblob blob;
BEGIN

    vblob := :new.IMG;

    IF(vblob IS NOT NULL)THEN
        /*-- this works
        imghash := sha2_string('0123456789',256); 
        :new.imghash := imghash; */

        /*-- this works too
        vblob := utl_raw.cast_to_raw('0123456789');
        imghash := sha2_blob(vblob,256);
        :new.imghash := imghash; */

        -- this DOES NOT work
        imghash := sha2_blob(vblob,256);
        :new.imghash := imghash;

    END IF;

END;
/

触发器本身起作用;它计算并在模拟数据(制造的字符串或blob)上插入哈希值,但在抛出以下错误时不在实际图像blob数据上：

ORA-29532: Java call terminated by uncaught Java exception: java.sql.sqlException: Invalid empty lob operation
ORA-06512: at “TEST.SHA2_BLOB”,line 1
ORA-06512: at “TEST.TR_IMG_UPSERT”,line 13
ORA-04088: error during execution of trigger ‘TEST.TR_IMG_UPSERT’

似乎触发器将：new.IMG数据读取为空blob.

为什么会发生这种情况？如何在每次在T_IMG表中插入或更新行时自动计算并将图像的哈希值插入到T_IMG表中？

注意：插入/更新数据行的客户端应用程序无法提供哈希值.

ADIM