java 如何读取clob

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.sql.Clob;

public List<Map<String, Object>> queryForList() {
  List<Map<String, Object>> rowList = new ArrayList<Map<String, Object>>();
  String driver = "";
  String url = "";
  String username = "";
  String password = "";
  String sql = "";
  log.info("查询sql条件：" + sql);
  try {
    // 加载驱动程序，此处运用隐式注册驱动程序的方法
    Class.forName(driver);
    log.info("加载驱动成功！");
  } catch (ClassNotFoundException e) {
    log.error("加载驱动程序，此处运用隐式注册驱动程序的方法出错：" + e.getMessage());
    e.printStackTrace();
  }
  try {
    // 创建连接对象
    Connection con = DriverManager.getConnection(url, username, password);
    // 创建sql执行对象
    Statement st = con.createStatement();
    // 执行sql语句并返回结果集
    ResultSet rs = st.executeQuery(sql);
    // 获得结果集结构信息,元数据
    ResultSetMetaData rsmd = rs.getMetaData();
    // 获得列数
    int columnCount = rsmd.getColumnCount();
    // 用于接收每行数据
    Map<String, Object> rowData = null;
    // clob类型
    Clob clob = null;
    // clob转成String
    String clobString = "";
    while (rs.next()) {
      rowData = new HashMap<String, Object>();
      for (int i = 1; i <= columnCount; i++) {
        // 判断数据类型是否为Clob
        if (rs.getObject(i) instanceof Clob) {// Clob转String
          clob = (Clob) rs.getObject(i);
          clobString = clob.getSubString((long) 1, (int) clob.length());
          rowData.put(rsmd.getColumnName(i), clobString);
        } else {
          rowData.put(rsmd.getColumnName(i), rs.getObject(i));
        }

      }
      rowList.add(rowData);
    }

    // 关闭相关的对象
    if (rs != null) {
      rs.close();
    }
    if (st != null) {
      st.close();
    }
    if (con != null) {
      con.close();
    }
  } catch (SQLException e) {
    e.printStackTrace();
  }
  return rowList;
}