Question

我正在Web应用程序中使用会话，问题是当我在一个会话中存储一个值时，使用另一个会话存储“最大”索引来跟踪ArrayList中保存的元素数。

ArrayList<String> list = new ArrayList<String>();

int a   =   (int) request.getSession().getAttribute("max");

System.out.print(a); // here a = 0 the first time 

list.add(request.getParameter("articolo")); // add a String value which in this case is a name of a product in my webapp

System.out.print((String) list.get(a)); // the just stored value gets printed

request.getSession().setAttribute("carrello" + a, list.get(a)); // add the just stored value in a session which is "carrello 0 " in this case

request.getSession().setAttribute("max", a+1);// increment the max index in session max

//list.clear();  i've also tried to do this to prevent the error 

request.getSession().setAttribute("messaggio","Prodotto aggiunto al carrello!");   // just a message saying " Product added to cart "

response.sendRedirect("visualizzaTab.jsp");  // redirect to a jsp page

我收到IndexOutOfBoundsException，向您保证在打印“购物车”会话中存储的每个产品后，最大会话值将设置为0。如果您需要更多代码，请在下面注释

Answer 1

由于以下几行，您的列表将始终为空：

ArrayList<String> list = new ArrayList<String>();

但是，因为您在以下行中将“ max”会话属性修改为1：

request.getSession().setAttribute("max", a+1);// increment the max index in session max

由于列表为空，因此任何后续请求到达以下代码行时，都会发生IndexOutOfBoundsException：

System.out.print((String) list.get(a)); // the just stored value gets printed

使用会话时出现IndexOutOfBoundsException

1 个答案: