利用结果集元数据将查询结果封装成Map

深碍√TFBOYSˉ_ 2022-08-09 01:50 203阅读 0赞

package cn.itcast.jdbc;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    public class ResultSetMetaDateTest {
    
        public static void main(String[] args) throws SQLException {
            System.out.println(read("select * from user where id<5"));
        }
    
        static List<Map<String, Object>> read(String sql) throws SQLException {
            Connection conn = null;
            PreparedStatement ps = null;
            ResultSet rs = null;
    
            try {
                conn = JdbcUtils.getConnection();
                ps = conn.prepareStatement(sql);
                rs = ps.executeQuery();
    
                ResultSetMetaData rsmd = rs.getMetaData();
                int count = rsmd.getColumnCount();
    
                String[]colNames=new String[count];
    
                for(int i=1;i<=count;i++){ 
    //              System.out.print(rsmd.getColumnClassName(i)+"\t");
    //              System.out.print(rsmd.getColumnName(i)+"\t");
    //              System.out.println(rsmd.getColumnLabel(i)); //ColumnLabel是别名，没有别名时就是ColumnName
    
                    colNames[i-1]=rsmd.getColumnName(i);
                }
    
                List<Map<String, Object>>datas=new ArrayList<Map<String,Object>>();
    
                while(rs.next()){
                    Map<String ,Object>data=new HashMap<String, Object>();
                    for(int i=0;i<colNames.length;i++){ 
                        data.put(colNames[i], rs.getObject(colNames[i]));
                    }
                    datas.add(data);
                }
    
                return datas;
            } finally {
                JdbcUtils.free(rs, ps, conn);
            }
        }
    }