Question

I’m designing a distributed network of sensing device. These devices will generate logs and send them to a central database. I’m using JMS for transporting log messages. The main database server will be running MDB(Message Driven Bean) to process incoming messages. The clients are sending data with GPRS. The problem is I don’t want my clients to process network problems. I need some relay service that runs locally on client machine and gets the message from client immediately without blocking it and try on behalf of it.(if network is down, try sending again after some time).

message is a simple java object:

public class Message {
    public int x;
    public int y;
    public int z;
}

client:

Message msg = new Message();
while (True) {
    /* sense data */
    msg = get_data_from_environment();

    /* send data to local relay service
     * This is non blocking call */
    relay_service.send(msg);
}

local relay service:

while (True) {
    /* get message from local client */
    msg = get_message_from_local_client();

    result = send_msg_to_JMS_server(msg);

    /* if not successful, persist it on a local queue and try some other time */
    if (result.is_sent() != True)
        store_msg_on_disk(msg);
}

Is there a message service like this or I should write relay service myself?

is this good to use JMS in this case? Should I design my own socket level protocol to send messages?

Answer 1

EDIT

Is there a message service like this or I should write relay service myself?

Typically these type of relay services you have to code your self, unless you are able to find a software that does exactly what you want it to do. This is not unusual to be done in these cases.

Is this good to use JMS in this case?

Yes, JMS is a very good solution to use as a middleware. You can have many clients connect to JMS and send messages to it. While you have a server program running reading the messages off the JMS and processing it and handling network problems if there are any. Also as a bonus the server program and send back messages to the client in case of complete failure.

Should I design my own socket level protocol to send messages?

I still do not know what kind of messages you want to send. If you are using a standard transport like SMTP or SMS or HTTP or something like that, there are libraries to help you send and verify delivery. If you have to send using a custom protocol then you would have to write you own socket level code.

Seeing your code examples shows me that you want to know if your client was successful in sending his message to the JMS. If it was not sent then save to disk and try again later.

JMS server will auto-acknowledge if the message received. You can check this from the JMS message or if it fails you will get a JMSException. If you save messages on disk you will need to know when to re-send them. You would need a timer or re-send on next message to send.