//查看
/*String tableName=""; //表名
String sql="select * from "+tableName; 
//连接数据库获取connection（一般单独写在一个工具类）
Connection conn = JdbcMysql.getConnection();
PreparedStatement stmt = conn.prepareStatement(sql);
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()){  //查询所有
    rs.getString("name");
}
rs.close();*/

//插入
/*String sql ="insert into idandpassword (stuid,password) values(?,?)";//或者在问号处可直接写入新数据
//连接数据库获取connection（一般单独写在一个工具类）
Connection conn = JdbcMysql.getConnection();
PreparedStatement stmt = conn.prepareStatement(sql); 
stmt.setString(1, "iddd");//数字1插入的信息对应上面的问号位置  
stmt.setString(2, "123");//插入的信息
stmt.executeUpdate();
stmt.close();*/


//查询
/*String sql = " SELECT * FROM images WHERE stuid = "+ stuid;  
//连接数据库获取connection（一般单独写在一个工具类）
Connection conn = JdbcMysql.getConnection();
PreparedStatement stmt = conn.prepareStatement(sql); 
ResultSet rs = stmt.executeQuery(sql);   
rs.next();
rs.getString("name");
rs.close();
*/



//修改 
/*
String sql ="update idandpassword  set password = ?, test = ? where stuid = ?";
//连接数据库获取connection（一般单独写在一个工具类）
Connection conn = JdbcMysql.getConnection();
PreparedStatement stmt = conn.prepareStatement(sql); 
stmt.setString(1,"aaaaa");//方法中1,2,3对应问号位置
stmt.setInt(2, 122);
stmt.setString(3,"zzz");
stmt.executeUpdate();
stmt.close();
*/

//删除
/*String sql ="delete from idandpassword where stuid= ?";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1,"ddd" );  //删除id="ddd"的数据
stmt.executeUpdate();
stmt.close();*/

关于关闭数据库连接： 
最好是在工具类写一个方法把conn，stmt，rs都关闭掉。 
JdbcMysql.closeAll(conn, stmt, rs);

原文地址https://blog.csdn.net/qq_42862882/article/details/81361741