介绍
我正在创建一个从oraclesql数据库上的Map对象读取的接口。到目前为止还不错，我成功地创建了类型和表，但是当用 java.sql.SQLData 它给了我这个铸造错误。
代码

public class EmpresaSqlData extends Empresa implements SQLData {

    private String sql_type = "USER.EMPRESA";

    public EmpresaSqlData() {}

    public EmpresaSqlData(String cif, String nom, Contacte contacte) {
        super(cif, nom, contacte);
    }    

    public EmpresaSqlData(String cif, String nom) {
        super(cif, nom);
    }

    @Override
    public String getSQLTypeName() throws SQLException {
        return sql_type;
    }

    @Override
    public void readSQL(SQLInput stream, String typeName) throws SQLException {
        sql_type = typeName;
        setNom(stream.readString());
        setCif(stream.readNString());//Write the object
        setContacte(stream.readObject(new Contacte)); //Fix??
    }

    @Override
    public void writeSQL(SQLOutput stream) throws SQLException {
        stream.writeString(getNom());
        stream.writeString(getCif());
        stream.writeObject(new ContacteSqlData());        
    }    
}

当我执行以下查询时，需要进行上述操作：

@Override
    public List<EmpresaSqlData> findAll() {
        EmpresaSqlData empresaSqlDataSQLData;
        List<EmpresaSqlData> corpList = new ArrayList<>();
        String query = "SELECT VALUE (e) FROM empreses e";

       try (Connection conn = cf.getConnection();
             PreparedStatement statement 
                    = conn.prepareStatement(query);){

            //Initial connection setup
            conn.setTypeMap(map);

            ResultSet rs = statement.executeQuery();

            while (rs.next()){      
                System.out.println(rs.getObject(1, EmpresaSqlData.class)); //Error here "Type of column not valid"
            }            

            return corpList;              

        } catch (SQLException e) {
            Logger.getLogger(EmpresaDAOImpl.class.getName()).log(Level.SEVERE, null, e);
            return null;
        }
    }

研究
从“implementing readsql（）and writesql（）methods”（ctrl+c和ctrl+f+enter）的文档中可以看出：

· The readSQL() method takes as input a SQLInput stream and a string that indicates the SQL type name of the data (in other words, the name of the Oracle object type, such as EMPLOYEE)

问题
然后我尝试读取 readSQL() 并将其转换为java对象 Contacte ```
setContacte((Contacte)stream.readObject());

这给了我一个例外：

Exception in thread "main" java.lang.ClassCastException: oracle.sql.STRUCT cannot be cast to activitat3.logica.Contacte
at activitat3.logica.EmpresaSqlData.readSQL(EmpresaSqlData.java:44)
at oracle.sql.STRUCT.toClass(STRUCT.java:662)
at oracle.sql.STRUCT.toJdbc(STRUCT.java:599)
at oracle.jdbc.driver.NamedTypeAccessor.getObject(NamedTypeAccessor.java:140)
at oracle.jdbc.driver.NamedTypeAccessor.getObject(NamedTypeAccessor.java:110)
at oracle.jdbc.driver.GeneratedStatement.getObject(GeneratedStatement.java:261)
at oracle.jdbc.driver.GeneratedScrollableResultSet.getObject(GeneratedScrollableResultSet.java:761)
at activitat3.dades.impl.EmpresaDAOImpl.findAll(EmpresaDAOImpl.java:184)
at activitat3.test.Main.llistarEmpreses(Main.java:330)
at activitat3.test.Main.main(Main.java:93)

此异常表示使用 `readSQL()` 方法来自 `java.sql.SQLData` 不能强制转换为java对象。
我怎么能用这种方式处理一个物体？
readint（）返回整数，readstring返回字符串，但readobject（）不能被强制转换或给定一个自定义对象？
目标
我想用这种方法从oraclesql数据库中读取Map对象。