用JDBC操纵BLOB和CLOB数据

在访问Oracle 数据库，对Oracle 的BLOB 和CLOB 进行操作的时候，当通过Oracle JDBC Driver 来调用的时，如下所例：


Driver myDriver = (Driver)


Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();


conn = myDriver.connect("jdbc:oracle:thin:" , props);


Statement stmt = conn.createStatement();


stmt.execute("select blob_content from lobtest where id=1");


ResultSet rs = stmt.getResultSet();


System.out.println("ResultSet result:"+rs);




while ( rs.next() ) ...{


System.out.println("BLOB:"+rs.getBlob("blob_content"));


myBlob = (oracle.sql.BLOB)rs.getBlob("blob_content");


}

返回的数据对象正确，是oracle.sql.BLOB 对象，然后可以使用该对象进行方法访问。
但当使用Oracle JDBC Driver 配置连接池后，使用DataSource 取得数据库连接之后，查询CLOB 数据，赋值给oracle.sql.CLOB 的对象，这是就会报类型转换错误。

在网络上有相应的解决方案，但都是依赖于某一种应用服务器所提供的oracle连接环境。
下面是一个比较好的解决方案：
1。必须有支持jdbc3.0以上规范的oracle驱动。
2。更新blob字段数据


public void updateBlob(String tableName, String blobFeild, String pryKey, String pryKeyValue, byte[] blob)




throws IOException, SQLException ...{


Statement stmt = null;


ResultSet rs = null;




try ...{


stmt = conn.createStatement();


String sql = "UPDATE " + tableName + " SET " + blobFeild + "=EMPTY_BLOB() WHERE " + pryKey + "='"


+ pryKeyValue + "'";


// 如果参数blob为null，清空blob值；否则先清空blob值，然后插入新的blob值。




if (blob == null) ...{


stmt.executeUpdate(sql);




} else ...{


stmt.executeUpdate(sql);


sql = "SELECT " + blobFeild + " FROM " + tableName + " WHERE " + pryKey + "='" + pryKeyValue


+ "' FOR UPDATE";


rs = stmt.executeQuery(sql);




if (rs.next()) ...{


Blob inBlob = rs.getBlob(blobFeild);


int len = inBlob.setBytes(1, blob);


log.debug("已成功保存BLOB大对象：" + len / 1024 + "KB");


}


}




} finally ...{


DbUtils.close(rs);


DbUtils.close(stmt);


}


}

3。获取blob字段数据




public byte[] findBlob(String tableName, String blobFeild, String pryKey, String pryKeyValue) throws SQLException ...{


byte[] blob = null;


Statement stmt = null;


String sql = "SELECT " + blobFeild + " FROM " + tableName + " WHERE " + pryKey + "='" + pryKeyValue + "'";


ResultSet rs = null;




try ...{


stmt = conn.createStatement();


rs = stmt.executeQuery(sql);




if (rs.next()) ...{


Blob outBlob = rs.getBlob(blobFeild);




if (outBlob != null && outBlob.length() > 0) ...{


blob = outBlob.getBytes(1, (int) outBlob.length());


}


}




} finally ...{


DbUtils.close(rs);


DbUtils.close(stmt);


}


return blob;


}

4。更新clob字段数据


public void updateClob(String tableName, String clobFeild, String pryKey, String pryKeyValue, String clob)




throws IOException, SQLException ...{


Statement stmt = null;


ResultSet rs = null;




try ...{


stmt = conn.createStatement();


String sql = "UPDATE " + tableName + " SET " + clobFeild + "=EMPTY_CLOB() WHERE " + pryKey + "='"


+ pryKeyValue + "'";


// 如果参数clob为null，清空clob值；否则先清空clob值，然后插入新的clob值。




if (clob == null) ...{


stmt.executeUpdate(sql);




} else ...{


stmt.executeUpdate(sql);


sql = "SELECT " + clobFeild + " FROM " + tableName + " WHERE " + pryKey + "='" + pryKeyValue


+ "' FOR UPDATE";


rs = stmt.executeQuery(sql);




if (rs.next()) ...{


Clob inClob = rs.getClob(clobFeild);


int len = inClob.setString(1, clob);


log.debug("已成功保存CLOB大对象：" + len / 1024 + "KB");


}


}




} finally ...{


DbUtils.close(rs);


DbUtils.close(stmt);


}


}

5。获取clob字段数据




public String findClob(String tableName, String clobFeild, String pryKey, String pryKeyValue) throws SQLException ...{


String clob = "";


Statement stmt = null;


String sql = "SELECT " + clobFeild + " FROM " + tableName + " WHERE " + pryKey + "='" + pryKeyValue + "'";


ResultSet rs = null;




try ...{


stmt = conn.createStatement();


rs = stmt.executeQuery(sql);




if (rs.next()) ...{


Clob outClob = rs.getClob(clobFeild);




if (outClob != null && outClob.length() > 0) ...{


clob = outClob.getSubString(1, pryKeyValue.length());


}


}




} finally ...{


DbUtils.close(rs);


DbUtils.close(stmt);


}


return clob;


}

采用以上这种方式可以避免对连接池提供方的依赖。