在这个封装的基础上，你可以帮我写出d a o层代码

好的，以下是根据你给出的类写出的简单的DAO层代码：

package chuanbo;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class ShipDao {
	
	// 根据id查询船只信息
	public shipmanag queryById(int id) {
		
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		shipmanag ship = null;
		
		try {
			conn = JdbcUtils.getConnection();
			String sql = "SELECT * FROM shipmanag WHERE shipId = ?";
			ps = conn.prepareStatement(sql);
			ps.setInt(1, id);
			rs = ps.executeQuery();
			if (rs.next()) {
				ship = new shipmanag();
				ship.setShipId(rs.getInt("shipId"));
				ship.setSize(rs.getString("size"));
				ship.setLeixing(rs.getString("leixing"));
				ship.setHuowu(rs.getString("huowu"));
			}
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			JdbcUtils.release(conn, ps, rs);
		}
		
		return ship;
	}
	
	// 插入一条船只信息
	public void insert(shipmanag ship) {
		
		Connection conn = null;
		PreparedStatement ps = null;
		
		try {
			conn = JdbcUtils.getConnection();
			String sql = "INSERT INTO shipmanag(shipId, size, leixing, huowu) VALUES(?, ?, ?, ?)";
			ps = conn.prepareStatement(sql);
			ps.setInt(1, ship.getShipId());
			ps.setString(2, ship.getSize());
			ps.setString(3, ship.getLeixing());
			ps.setString(4, ship.getHuowu());
			ps.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			JdbcUtils.release(conn, ps, null);
		}
	}
	
	// 更新一条船只信息
	public void update(shipmanag ship) {
		
		Connection conn = null;
		PreparedStatement ps = null;
		
		try {
			conn = JdbcUtils.getConnection();
			String sql = "UPDATE shipmanag SET size = ?, leixing = ?, huowu = ? WHERE shipId = ?";
			ps = conn.prepareStatement(sql);
			ps.setString(1, ship.getSize());
			ps.setString(2, ship.getLeixing());
			ps.setString(3, ship.getHuowu());
			ps.setInt(4, ship.getShipId());
			ps.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			JdbcUtils.release(conn, ps, null);
		}
	}
	
	// 删除一条船只信息
	public void delete(int id) {
		
		Connection conn = null;
		PreparedStatement ps = null;
		
		try {
			conn = JdbcUtils.getConnection();
			String sql = "DELETE FROM shipmanag WHERE shipId = ?";
			ps = conn.prepareStatement(sql);
			ps.setInt(1, id);
			ps.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			JdbcUtils.release(conn, ps, null);
		}
	}
}

这个DAO层代码中包含了四个方法，分别是查询、插入、更新和删除船只信息。在这些方法中，我们通过使用JDBC连接数据库并执行相应的SQL语句来实现对数据库的操作。需要注意的是，这里的JdbcUtils是一个自定义的工具类，用于获取数据库连接和释放资源。