Question

我需要在AppEngine中创建一个TCP连接（在服务器端）并使其无限期保持活动（或至少约30分钟）。我创建了一个后台线程，打开了java.net.Socket并尝试读取包含BufferedReader的行。在大约3秒钟不活动后，我得到以下异常：

java.net.SocketException: Socket operation timed out: The API call remote_socket.Receive() took too long to respond and was cancelled.

我将在下面使用代码I的骨架。任何帮助将不胜感激（包括GAE中套接字限制的变通方法或信息）。谢谢！

    ThreadFactory tm = ThreadManager.backgroundThreadFactory();
    thread = tm.newThread(new Runnable() {
        @Override
        public void run() {
            Socket socket = null;
            try {
                socket = new Socket("localhost", 8000);
                socket.setSoTimeout(0);
                socket.setKeepAlive(true);
                BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));

                String in = reader.readLine();
                // execution never gets past here
                //...
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                // ... <close socket>
            }
        }
    });
    thread.start();

如果它是相关的，那么就是用例：我有一个TCP服务器，它曾经在客户端使用嵌入式Applet。我想将Applet重新设计为webapp，但服务器仍能正常工作，所以我宁愿不改变它。我想编写一个简单的servlet来保持TCP连接的活动，并在TCP服务器和GWT客户端之间来回传递消息。

Answer 1

由于安全原因，套接字在GAE 中有很多限制，但GAE提供了许多现成的服务，这些服务需要使用套接字，例如电子邮件，xmpp等。 / p>

首先，您的应用需要付费应用，表示必须启用结算才能在GAE上使用套接字

您可以拥有look here for how to use sockets in java on GAE

以下是针对套接字限制的Google应用引擎文档的摘录：

App Engine支持套接字，无需您导入任何套接字特殊的App Engine库或添加任何特殊的App Engine代码。但是，您需要有一些限制和行为了解何时使用套接字：

Sockets are available only for paid apps.
You cannot create a listen socket; you can only create outbound sockets.
java.net.URL is still configured to use the URL Fetch API; there is currently no way around this.
Most classes in javax.net.ssl are supported.
You can only use TCP or UDP; arbitrary protocols are not allowed.
You cannot bind to specific IP addresses or ports.
Port 25 (SMTP) is blocked; you can still use authenticated SMTP on the submission port 587.
Private, broadcast, multicast, and Google IP ranges (except those whitelisted below), are blocked:
    Google Public DNS: 8.8.8.8, 8.8.4.4, 2001:4860:4860::8888, 2001:4860:4860::8844 port 53
    Gmail SMTPS: smtp.gmail.com port 465 and 587
    Gmail POP3S: pop.gmail.com port 995
    Gmail IMAPS: imap.gmail.com port 993
Socket descriptors are associated with the App Engine app that created them and are non-transferable (cannot be used by other apps).
Sockets may be reclaimed after 2 minutes of inactivity; any socket operation keeps the socket alive for a further 2 minutes.
You cannot Select between multiple available sockets because that requires java.nio.SocketChannel which is not currently supported.)

GAE保持套接字活着

1 个答案: