我的要求是管理员应该向所有登录用户发送数据。我有一个 servlet 第一个用户发送登录 HTTP 请求并从 servlet 获取登录成功响应，现在该用户的会话已启动。类似地其他用户登录。现在管理员也是一个用户可以登录并看到两个用户 user1 和 user2 登录. 管理员应该向所有登录的用户发送数据。Servlet 应该在没有用户 HTTP 请求的情况下将数据推送给该用户。请注意在会话期间用户不会发送任何其他 HTTP 请求。
我尝试存储每个登录用户的响应 obj 而不是彗星，然后使用该 obj 尝试将数据发布回用户，但这没有用。
请检查以下代码：LoginServlet.java
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
ServletContext sc;
protected ArrayList<HttpServletResponse> connections = new ArrayList<HttpServletResponse>();
public LoginServlet() {
super();
}
public void init() throws ServletException {
super.init();
sc = getServletContext();
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
}
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
synchronized (connections) {
connections.add(response);
}
ServletContext sc = getServletContext();
Integer x = (Integer) sc.getAttribute("hit");
if (x == null)
x = 1;
else
x++;
sc.setAttribute("hit", x);
String username = request.getParameter("username");
String password = request.getParameter("password");
HttpSession session = request.getSession(true);
session.setAttribute("username", username);
session.setAttribute("password", password);
response.setContentType("text/html");
ArrayList<LoggedInUser> loggedInUsers = (ArrayList<LoggedInUser>) sc
.getAttribute("users");
if (loggedInUsers == null) {
System.out.println("loggedInUsers creates");
loggedInUsers = new ArrayList<LoggedInUser>();
}
loggedInUsers.add(new LoggedInUser(username, password));
sc.setAttribute("users", loggedInUsers);
PrintWriter out = response.getWriter();
System.out.println("loggedInUsers ==>" + loggedInUsers.size());
if (username != null && username.equals("admin")) {
out.println("Admin Login Success");
ServletContext scx = getServletContext();
Integer xx = (Integer) scx.getAttribute("hit");
out.println("<H1>Users visited " + xx + "</h1>");
loggedInUsers = (ArrayList<LoggedInUser>) sc.getAttribute("users");
for (int i = 0; i <= loggedInUsers.size() - 1; i++) {
LoggedInUser LoggedInUser = loggedInUsers.get(i);
out.println(LoggedInUser.getmUsername()+ "<br>");
}
for (int i = 0; i < connections.size(); i++) {
try {
LoggedInUser LoggedInUser = loggedInUsers.get(i);
PrintWriter writer = connections.get(i).getWriter();
System.out.println("inside loope " + i + "\n" + writer);
writer.println("MESSAGE FROM ADMIN HERE" + "<br>");
writer.flush();
writer.close();
} catch (IOException e) {
log("IOExeption sending message", e);
}
}
} else {
out.println("Welcome " + username + " Login Success");
}
}
}
一旦用户登录 arraylist 中存储的 resp obj。
synchronized (connections) {
connections.add(response);
}
后来使用那个 obj 得到了 printwriter obj。
PrintWriter writer = connections.get(i).getWriter();
问题：
- 如何向所有登录用户发送一个特定的消息？
- 没有彗星，我们能做到这一点吗？
如果我做错了什么，请更正代码并提供其他建议。谢谢