将JDBC ResultSet结果集转成List

将JDBC ResultSet结果集转成List

import java.io.IOException;
import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Created by xh on 17-7-26.
 * 随机读取数据库中的size条记录，注意，tableName及记录的条数作为参数传入，所以需要用到字符串拼接，StringBuffer()
 * append()方法，另外需要转换成字符串的时候使用.toString()即可
 */
public class ReadSqlrecorderRandom {
    public static void main(String[] args) throws IOException {
        getRecordsRandom("jdbc:mysql://localhost:3306/xyj","User",2);
    }
    public static List<Map<String,Object>> getRecordsRandom(String url, String tableName, int size) throws IOException {
        Connection con = null;
        PreparedStatement pst = null;
        ResultSet rs = null;
        String user = "root";
        String password = "123456";
        List<Map<String,Object>> list = new ArrayList<Map<String, Object>>();
        try {

            con = DriverManager.getConnection(url, user, password);
            StringBuffer sql=new StringBuffer("SELECT * FROM  ");
            if(tableName !=null){
               sql.append(tableName);
               sql.append(" order by rand() LIMIT ");
               sql.append(size);
            }

            pst = con.prepareStatement(sql.toString());
            rs = pst.executeQuery();
            ResultSetMetaData md = rs.getMetaData(); //获得结果集结构信息,元数据
            int columnCount = md.getColumnCount();   //获得列数

            while (rs.next()) {
                
                Map<String,Object> rowData = new HashMap<String,Object>();

                for(int i = 1;i<=columnCount;i++){
                    rowData.put(md.getColumnName(i), rs.getObject(i));
                }
                //System.out.println(rowData);
                list.add(rowData);         //之前rowData在while外面，list.add（）重复引用，指向同一块内存，所以值被覆盖，重复出现后面的值
            }
        } catch (SQLException ex) {
            ex.printStackTrace();
        } finally {
            try {
                if (rs != null) {rs.close();rs=null;}
            } catch (SQLException ex) {
                ex.printStackTrace();
            }
        }
        System.out.println(list);
        return  list;
    }
}