Jdbc 链接数据库

代码 ：

try {
    PreparedStatement ps =null;
    ps = conn.prepareStatement("Select * from cp_cpxx where rownum<2");
    ResultSet rs = null;
    rs = ps.executeQuery();
    while(rs.next()){
     System.out.println("cpbm ->" + rs.getObject(1));
    }
    rs.close();
    ps.close();
    conn.close();
    try{
    if(rs.next()){
    }}catch(Exception e){
     System.err.println("资源已经释放！");
    }
    if(rs != null){System.out.println("ps is not null");}
    if(ps!=null){System.out.println("rs is not null");}
    if(conn != null){System.out.println("conn is not null");}
   } catch (SQLException e) {
    e.printStackTrace();
   }
//  

 

Console:

       cpbm ->09110444    
       资源已经释放！
       ps is not null
       rs is not null
       conn is not null

 问：ResultSet，PreparedStatement,Connection 关闭后 怎么判断不为null,还有请问下关闭顺序有错吗？