oracle.sql.CLOB cannot be cast to weblogic.jdbc.vendor.oracle.OracleThinClob

if (rs.next()) {
        java.sql.Clob clob = rs.getClob(1);
        BufferedInputStream dataInput = new BufferedInputStream(ins,
            MAX_BUFFER_SIZE);
        // 使用了Weblogic的CLOB实现
        OutputStream outs = ((weblogic.jdbc.vendor.oracle.OracleThinClob) clob).getAsciiOutputStream(); --这边报错

Q1:这边明明是java.sql.Clob转成OracleThineClob却报错java.lang.ClassCastException: oracle.sql.CLOB cannot be cast to weblogic.jdbc.vendor.oracle.OracleThinClob

Q2:什么情况会导致java.lang.ClassCastException: oracle.sql.CLOB cannot be cast to weblogic.jdbc.vendor.oracle.OracleThinClob这种报错？

补充：
Weblogic server 12.2.1.4
JDK1.8
有ojdbc7.jar

把clob转换字符数组，用to_char转换一下，参考：https://www.cnblogs.com/lishupeng/p/6382225.html