在java中从对象表检索结构类型

您好，我需要从oracle对象表（address）获取值，为此，我想将java类（address）映射为oracle类型（address）。从Jframe中的一个按钮，我可以看到打印al数据的内容。因此：

Sql:

创建或替换
键入地址作为对象(
无varchar2（7），
str varchar2（40），
瓦查尔市2（25），
瓦查尔国家2（25）
);

create table airp (id_pk number(5),
location address_t);

Java地址类：

import test.Test;
import java.sql.Connection;
import java.sql.SQLData;
import java.sql.SQLException;
import java.sql.SQLInput;
import java.sql.SQLOutput;
import java.util.logging.Level;
import java.util.logging.Logger;


public class Address implements SQLData {
  private String str;
  private String no;
  private String city;
  private String country;
  private String sql_type;
  private Connection conn = null;

  public Address(){

  }

  public Address(String sql_type, String no, String str, String city , String country){
      this.sql_type = sql_type;
      this.no = no;
      this.str = str;
      this.city = city;
      this.country = country;  

  }

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

    @Override
    public void readSQL(SQLInput stream, String typeName) throws SQLException {
        this.sql_type = typeName;
        no = stream.readString();
        str = stream.readString();
        city = stream.readString();
        country = stream.readString();

    }

    @Override
    public void writeSQL(SQLOutput stream) throws SQLException {
        stream.writeString(no);
        stream.writeString(str);
        stream.writeString(city);
        stream.writeString(country);

    }

    @Override
    public String toString(){
        return sql_type+" "+no+" "+" "+city+" "+country;

    }

}

和按钮：

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

                try {

                    java.util.Map map = con.getTypeMap();
                    map.put("LI.ADDRESS_T", Class.forName("test.Address"));
                    con.setTypeMap((Map)map);
                    map = con.getTypeMap();

                    sql = "select * from aerop";
                    st = (OracleStatement)con.createStatement();
                    rs = (OracleResultSet)st.executeQuery(sql);

                    while(rs.next()){
                        System.out.println(rs.getObject(1));
                    }
                } catch (SQLException ex) {
                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                } catch (ClassNotFoundException ex) {

                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                }}

我得到下一个错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at test.Test.jButton1ActionPerformed

con
或
con.getTypeMap（）
为
null
。你为什么不调试它？
什么？你是在讽刺还是真的这么想？：）我已经做了差不多两个小时了，因为我已经声明了连接，但是我忘记了创建它，新手错了