java原生jdbc读取mysql数据库的数据

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

public class ReadDB {

    public List<String> query() {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        String sql = " select * from compare; ";
        List<String> mapList = new ArrayList<String>();
        try
        {
            conn = DBHelper.getConnection();
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            while(rs.next())
            {
                mapList.add(rs.getString("id"));
            }
            return mapList;
        }
        catch(Exception e)
        {
            e.printStackTrace();
            return null;
        }
        finally
        {
            if(rs!=null)
            {
                try
                {
                    rs.close();
                    rs = null;
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
            if(stmt!=null)
            {
                try
                {
                    stmt.close();
                    stmt = null;
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        }
    }
}