java—将查询的结果封装成List与用回调函数实现数据的动态封装（44）

package cn.itcast.dbutils;

import java.sql.Connection;
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 javax.sql.DataSource;

public class QueryRunner {
    //接收一个ds
    private DataSource ds;
    public QueryRunner() {
    }
    public QueryRunner(DataSource ds) {
        this.ds = ds;
    }
    /**
     * 只封装成List<Map>
     */
    public List<Map<String,Object>> query(String sql){
        //封装数据用
        List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();//声明返回的对象
        Connection con = null;
        try{
            con = ds.getConnection();
            //执行查询
            Statement st = con.createStatement();
            ResultSet rs = st.executeQuery(sql);
            //分析结果集
            ResultSetMetaData rsmd = rs.getMetaData();
            //获取列数
            int cols = rsmd.getColumnCount(); 
            //遍历数据
            while(rs.next()){
                //一行数据
                Map<String,Object> mm = new HashMap<String, Object>();
                //遍历列
                for(int i=0;i<cols;i++){
                    //获取列名
                    String colName = rsmd.getColumnName(i+1);
                    //获取数据
                    Object val     = rs.getObject(i+1);
                    //封装到map
                    mm.put(colName, val);
                }
                //将这个map放到list
                list.add(mm);
            }
            
        }catch(Exception e){
            throw new RuntimeException(e);
        }finally{
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return list;
    }
}