java jdbc与mysql为什么连接不上并且抛出空指针异常？

jdbc连接代码：

public class ConnDB{
     Connection conn=null;
     Statement stmt=null;
     ResultSet rs=null;
        public ConnDB(){
                try{
                        Class.forName("com.mysql.jdbc.Driver");
                }catch(java.lang.ClassNotFoundException e){
                        System.err.println(e.getMessage());
                }
        }
 /***************************************************
        *method name:    executeQuery()
        *功能:执行查询操作
        *return value: ResultSet
 * @throws ClassNotFoundException 
****************************************************/
        public  ResultSet executeQuery(String sql) {
                try{
                //    conn=getConnection();
                    // Class.forName("com.mysql.jdbc.Driver");
                    conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/database?user=root&password=root&useUnicode=true");
                    //JDBConnection connection=new JDBConnection(); 
                    //conn=connection.getConnection();
                    stmt=conn.createStatement();
                        rs=stmt.executeQuery(sql);
                }catch(Exception ex){
                        System.err.println(ex.getMessage());
                        }finally{}
                return rs;
        }
 /***************************************************
        *method name:    close()
        *功能:关闭数据库链接
        *return value:     void
****************************************************/
       public void close(){
         try {
           if (rs != null) rs.close();
         }
         catch (Exception e) {
           e.printStackTrace(System.err);
         }finally{
         try {
           if (stmt != null) stmt.close();
         }
         catch (Exception e) {
           e.printStackTrace(System.err);
         }finally{
         try {
           if (conn != null) {
             conn.close();
           }
         }
          catch (Exception e) {
           e.printStackTrace(System.err);
         }       
          
         }
       }
       }

}

查询代码：

public int checkManager(String name,String inpwd) {
    int flag = 0;
    ConnDB conn=new ConnDB();
    String sql = "SELECT * FROM admin where username='" +name + "'";
    System.out.println(sql);
    ResultSet rs = conn.executeQuery(sql);
   
    try {
        if (rs.next()) {
            String pwd = inpwd;
            if (pwd.equals(rs.getString(3))) {
                flag = 1;
                rs.last();
                int rowSum = rs.getRow();
                rs.first();
                if (rowSum != 1) {
                    flag = 0;
                    System.out.print("获取的row的值：" + sql + rowSum);
                }
            } else {
                flag = 0;
            }
        }else{
            flag = 0;
        }
    } catch (SQLException ex) {
        flag = 0;
    }
   // ConnDB.close(rs, st, conn);
    conn.close();
    return flag;
}

在  if (rs.next()) 处报空指针