DBUtils之查询（二）

• 使用ColumnListHandler

public static void columnListHandler() throws SQLException {
        Connection con = MyJDBCUtiles.getConnection();
        QueryRunner qr = new QueryRunner();
        String sql = "select username,password from userinfo where age = ?";
        //注意sql语句中的筛选项(username,password)一定要包括下列list中的参数项(username)
        Object [] param = {29};
        List<Object> list = qr.query(con,sql,new ColumnListHandler<Object>("username"),param);
        //若没有查询到则list.size()=0
        for (Object o : list){
            System.out.println(o + "\t");
        }

    }

• 结果

• 使用ScalarHandler

public static void scalarHandler() throws SQLException {
        Connection con = MyJDBCUtiles.getConnection();
        String sql = "select count(*) from userinfo where age = ?";
        QueryRunner qr = new QueryRunner();
        Object [] param = {21};
        long o = qr.query(con,sql,new ScalarHandler<Long>(),param);
        //若未查询到，则o的值为0
        System.out.println(o);

}

• 结果

•  使用MapHandler

　　Map<键，值>：键为列名，值为列的属性值

public static void mapHandler() throws SQLException {
        Connection con = MyJDBCUtiles.getConnection();
        String sql = "select * from userinfo where age = ?";
        Object[] param = {21};
        QueryRunner qr = new QueryRunner();
        Map<String,Object> map = qr.query(con,sql,new MapHandler(),param);
        for(String key : map.keySet()){
            System.out.println(key+">>>"+map.get(key));
        }
　　　　　

}

• 结果

• 使用MapListHandler

public static void mapListHandler() throws SQLException {
        Connection con = MyJDBCUtiles.getConnection();
        String sql = "select * from userinfo where age = ?";
        Object[] param = {21};
        QueryRunner qr = new QueryRunner();
        List<Map<String,Object>> list = qr.query(con,sql,new MapListHandler(),param);
        for(Map<String,Object> map : list){
            for(String key : map.keySet()){
                System.out.print(key+":"+map.get(key)+"\t");
            }
            System.out.println();
        }　　　

}

• 结果

 ^_^