java - 如何按插入顺序添加和删除 HashMap 值？

Question

我想知道如何根据用户的唯一 ID 和 ID session 来映射连接的用户，以便当该 ID 的 session 超过 3 个时，首先连接的用户将从 hashmap 中删除，依此类推.

例子:

UserID:3 Session:1980002
UserID:3 Session:2841111
UserID:3 Session:84848

UserID 已经包含 3 个 Activity session ，最旧的 session 被删除并调用 KillSession，让位于新 session 。

UserID:3 Session:2841111
UserID:3 Session:84848
UserID:3 Session:4848880

代码:

public void onHTTPCupertinoStreamingSessionCreate(HTTPStreamerSessionCupertino httpSession) {
    String User_Session = httpSession.getSessionId();
    String Client_ID = httpSession.getProperties().getPropertyStr("sql_client_id");
    /* Verifies that there are already 3 active sessions and removes the oldest, 
    since the limit of simultaneous sessions is 3 for each user,
    and add to hashmap, Client_ID and User_Session */
}

public void onHTTPCupertinoStreamingSessionDestroy(IHTTPStreamerSession httpSession) {
    String User_Session = httpSession.getSessionId();
    //remove from hashmap, Client_ID based on session User_Session
}

public void KillSession(int SessionId){ 
    IApplicationInstance Instance = applicationInstance;
    IHTTPStreamerSession sessions = Instance.getHTTPStreamerSessions().get(SessionId);
    sessions.rejectSession();
    //remove from hashmap, Client_ID based on session User_Session
}

Client_ID是用户在数据库中的id，User_Session是wowza中为每次连接生成的唯一session，这个session是不等值的，即如果同一个Client_ID连接多次，则每个 session 的值都会不同。

也就是说，基本上我的困难是挂载hashmap，我怎么能这样做？

Answer 1

如果要按插入顺序添加和删除，请使用 LinkedHashMap。(可能有用的简单版本)

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample {
    static class User {
        LinkedHashMap<String, Integer> sessionIds = new LinkedHashMap<>();
        int userId;

        public User(int userId) {
            this.userId = userId;
        }

        public void addSession(String someField, int sessionId) {
            this.sessionIds = new LinkedHashMap<String, Integer>(sessionIds) {
                protected boolean removeEldestEntry(Map.Entry<String, Integer> eldest) {
                    return size() > 3;
                }
            };
            sessionIds.put(someField, sessionId);
        }

        @Override
        public String toString() {
            return "User{" +
                    "sessionIds=" + sessionIds +
                    ", userId=" + userId +
                    '}';
        }
    }

    public static void main(String[] args) {
        User user1 = new User(1);
        user1.addSession("1980002", 1980002);
        user1.addSession("84848", 84848);
        user1.addSession("2841111", 2841111);
        System.out.println(user1);
        user1.addSession("999999", 999999);
        System.out.println(user1);
        user1.addSession("777777", 777777);
        System.out.println(user1);
    }
}