Java 如何使用 Atmosphere 设计推送通知

How to design push notifications using Atmosphere

提问by Saurabh Kumar

I want to use atmosphere to develop a notification System.

我想用大气来开发一个通知系统。

I am very new to Atmosphere so apologies if I am wrong somewhere. What i understood is when a Actor publishes something I save the notification action to the database. What i don't understand how the receiver will receive those notifications in realtime.

我对 Atmosphere 很陌生，所以如果我在某处错了，我深表歉意。我的理解是，当演员发布某些内容时，我会将通知操作保存到数据库中。我不明白接收者将如何实时接收这些通知。

The sender i know will do something like following

我认识的发件人将执行以下操作

event.getBroadcaster().broadcast(
            objectMapper.writeValueAsString("Some Message"));

Now i am not able to figure out how the receiver can receive this message.

现在我无法弄清楚接收者如何接收此消息。

For example . I want to add a User Object as Friend. So when User1 adds User2 User1 broadcast but than how i push the notification to User2. I have difficulty in understanding this.

例如 。我想添加一个用户对象作为朋友。因此，当 User1 添加 User2 User1 广播时，而不是我如何将通知推送到 User2。我很难理解这一点。

Technically i want something similar like facebook or gmail notification where on user activity other users get notifications.

从技术上讲，我想要类似 facebook 或 gmail 通知的东西，在用户活动中，其他用户会收到通知。

采纳答案by elusive-code

Basically what you need is to implement Publish-subscribeon top of Atmosphere.

基本上你需要的是在 Atmosphere 之上实现发布订阅。

Atmosphere consists of two parts: client-side (javascript-based) and server-side(java-based).

Atmosphere 由两部分组成：客户端（基于javascript）和服务器端（基于java）。

First of all you need to configure server-side: Installing Atmosphere

首先你需要配置服务器端：安装大气

Namely servlet or filter, it is required so that it could add AtmosphereResourceto the HttpServletRequest.

即 servlet 或过滤器，它是必需的，以便它可以将AtmosphereResource添加到HttpServletRequest。

AtmosphereResourcerepresents a single client connection on the server-side.

AtmosphereResource表示服务器端的单个客户端连接。

Broadcasteris actually a container for these resources, so that you don't need to handle lookup/iteration/concurrency when you need to send to multiple connections. (Note that multiple connections can be produced by single client).

Broadcaster实际上是这些资源的容器，所以当你需要发送到多个连接时，你不需要处理查找/迭代/并发。（请注意，单个客户端可以产生多个连接）。

On the server-side you need to provide clients an endpoint to subscribe for notifications. For example, if you are using Spring-MVC, it could go like this (omitting validations/authentications, etc.):

在服务器端，您需要为客户端提供一个端点来订阅通知。例如，如果您使用的是 Spring-MVC，它可能是这样的（省略验证/身份验证等）：

@RequestMapping(value = "/user-notifications/{userId}")
@ResponseStatus(HttpStatus.OK)
@ResponseBody
public void watch(@PathVariable("userId") String userId,
                  HttpServletRequest request) throws Exception {
    //Atmosphere framework puts filter/servlet that adds ATMOSPHERE_RESOURCE to all requests
    AtmosphereResource resource = (AtmosphereResource)request.getAttribute(ApplicationConfig.ATMOSPHERE_RESOURCE);

    //suspending resource to keep connection
    resource.suspend();

    //find broadcaster, second parameter says to create broadcaster if it doesn't exist
    Broadcaster broadcaster = BroadcasterFactory.getDefault().lookup(userId,true);

    //saving resource for notifications
    broadcaster.addAtmosphereResource(resource);
}

When something happens you can notify clients like this:

当发生某些事情时，您可以像这样通知客户：

public void notify(User user, Event event){
    Broadcaster b = BroadcasterFactory.getDefault().lookup(user.getId());
    if (b!=null){
        b.broadcast(event);
    }
}

On the client side you need to send a subscribe request and listen for subsequent events, like this:

在客户端，您需要发送订阅请求并监听后续事件，如下所示：

var request = new atmosphere.AtmosphereRequest();
request.url = '/user-notifications/'+userId;
request.transport = 'websocket';
request.fallbackTransport = 'streaming';
request.contentType = 'application/json';
request.reconnectInterval = 60000;
request.maxReconnectOnClose = 1000;
request.onMessage = function(response){
    console.log(response);
    alert('something happend<br>'+response);
};
that.watcherSocket = atmosphere.subscribe(request);

So, to sum it up:

所以，总结一下：

1. Client sends request "I want to receive this kind of notifications".
2. Server receives request, suspends and saves connection somewhere (either in your code or in Broadcaster).
3. When something happens server looks for suspended connection and sends notification in it.
4. Client receives notification and callback is invoked.
5. Profit!!!

1. 客户端发送请求“我想接收此类通知”。
2. 服务器接收请求，在某处（在您的代码或广播中）暂停并保存连接。
3. 当发生某些事情时，服务器会查找挂起的连接并在其中发送通知。
4. 客户端收到通知并调用回调。
5. 利润！！！

This wikihas explanations for some concepts behind Atmosphere and links to other documentation.

这个 wiki解释了 Atmosphere 背后的一些概念，并链接到其他文档。

回答by Dario

Atmosphere supports WebSocket. If you want to write a java client you may want to try https://github.com/TooTallNate/Java-WebSocket

Atmosphere 支持 WebSocket。如果你想写一个 java 客户端，你可能想尝试https://github.com/TooTallNate/Java-WebSocket

See section Writing your own WebSocket Client

请参阅编写您自己的 WebSocket 客户端部分