所有字符串都是“????“从对象类型的Oracle检索表时

当我试图从Oracle过程中检索对象类型时,我会收到正确的数字,但是这个过程传递给我的所有字符串都是“???”. 我的例子:

import oracle.sql.ARRAY;
import oracle.sql.ArrayDescriptor;
import oracle.sql.STRUCT;
import oracle.sql.StructDescriptor;

import java.sql.Array;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSetMetaData;
import java.sql.Struct;
import java.sql.Types;

public class InitMethod {

    public static void init() throws Exception {
        Class.forName("oracle.jdbc.OracleDriver");
        Connection connection =
                DriverManager.getConnection("jdbc:oracle:thin:@10.0.0.20:1521:dw", "user", "password");

        final String typeName = "T_DEMO_OBJECT";
        final String typeTableName = "T_DEMO_OBJECTS";

        final StructDescriptor structDescriptor = StructDescriptor.createDescriptor(typeName.toUpperCase(), connection);
        final ResultSetMetaData metaData = structDescriptor.getMetaData();

        CallableStatement cs = connection.prepareCall("{call p_generate_demo_objects(?, ?)}");
        cs.setInt(1, 7);

        cs.registerOutParameter(2, Types.ARRAY, typeTableName);
        cs.execute();

        Object[] data = (Object[]) ((Array) cs.getObject(2)).getArray();
        for (Object tmp : data) {
            Struct row = (Struct) tmp;

            int idx = 1;
            for (Object attribute : row
                    .getAttributes()) {
                System.out.println(metaData.getColumnName(idx) + " = " + attribute);
                ++idx;
            }
            System.out.println("---");
        }
        cs.close();
}

我收到正确的数字,但所有字符串都是“?“?”:

some_number=1 some_string=????

some_number=2 some_string=????

有什么问题吗?

(我使用ojdbc6.jar)