[英]getServletContext().getAttribute() resets value?
以下代碼是我的示例servlet應用程序
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String userEmail = request.getPathInfo().split("/")[1];
saveEmails(response, userEmail);
}
protected void saveEmails(HttpServletResponse response, String email) {
ArrayList<String> userEmails = (ArrayList<String>)getServletContext().getAttribute("userEmails");
if (userEmails == null) {
System.out.println("creating a new linked list");
ArrayList<String> newUserEmails = new ArrayList<String>();
newUserEmails.add(email);
getServletContext().setAttribute("userEmails", newUserEmails);
} else {
System.out.println("appending new email into linked list");
getServletContext().setAttribute("userEmails", userEmails.add(email));
}
System.out.println(userEmails);
}
每當我發出第一個(localhost / value1)和第二個(localhost / value2)請求時(getServletContext().getAttribute("userEmails"))
打印以下內容
[value1]
[value1,value2]
但是,每當我發出第三個(localhost / value3)請求時,它總是將LinkedList轉換為布爾值並輸出以下錯誤
HTTP Status 500 - java.lang.Boolean cannot be cast to java.util.LinkedList
我不確定發生了什么,是否需要在web.xml中配置某些內容?
List.add()
返回一個布爾值,因此第二次調用userEmails.add(email)
該屬性將替換為Boolean
。
第一次將屬性放入上下文中后,無需繼續設置屬性(除非您要替換整個列表)。 只需更換
getServletContext().setAttribute("userEmails", userEmails.add(email));
與
userEmails.add(email);
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