IoTF service（a special MQTT Broker） Connectivity for Applications and Devices
这里先说一下特殊情况，可能需要在同一端需要subscribe和publish，这里也说一下。
1. 如果subscribe和publish都在device端：
//Subscribe the Command events
//iot-2/cmd/<cmd-type>/fmt/<format-id>
handler.subscribe("iot-2/cmd/" + MqttUtil.DEFAULT_CMD_ID +"/fmt/json",0);
//Publish device events to theapp
//iot-2/evt/<event-id>/fmt/<format>
handler.publish("iot-2/evt/" + MqttUtil.DEFAULT_EVENT_ID
+ "/fmt/json", jsonObj.toString(), false, 0);
2. 如果subscribe和publish都在app端：
//Subscribe Device Events
//iot-2/type/<type-id>/id/<device-id>/evt/<event-id>/fmt/<format-id>
handler.subscribe("iot-2/type/" + MqttUtil.DEFAULT_DEVICE_TYPE
+ "/id/+/evt/" + MqttUtil.DEFAULT_EVENT_ID + "/fmt/json",0);
//Publish command to onespecific device
//iot-2/type/<type-id>/id/<device-id>/cmd/<cmd-id>/fmt/<format-id>
handler.publish("iot-2/type/" + MqttUtil.DEFAULT_DEVICE_TYPE
+ "/id/" + deviceid + "/cmd/" + MqttUtil.DEFAULT_CMD_ID
+ "/fmt/json", jsonObj.toString(), false, 0);
其实正是这两个特殊情况，我们可以扩展出来下面的两种情况：
1.订阅端在device，发布端在app；
2.订阅端在App，发布端在device。
Note：实际上，完全可以把两端（设备和服务器）都当做app，或者多当做device，技术上完全是可行的，只要是同一个IoTBroker（其他的MQTTBroker不符合这里的topic规则），就是topic怎么指定的事儿。但是这样有点不符合大众的逻辑思维，一般情况下，用的比较多的scenario是设备采集数据，向服务器端发送数据（在这里叫发布消息），即第2种情况。不论谁是订阅端，在订阅时都要有一个监听器，不断的监听发布端传过来的消息数据，拿到后根据需求做相应处理。
1.Device/Sensor send message to App（订阅端在App，发布端在device)：
Subscribingto device events
An application can subscribe toevents from oneor more devices.
- Subscribe to topic iot-2/type/device_type/id/device_id/evt/event_id/fmt/format_string
Note
The MQTT “any” wildcard character (+) may be usedfor any of the following components if you want to subscribe to more than onetype of event, or events from more than a single device.
- device_type
- device_id
- event_id
- format_string
eg. Subscribeto topic iot-2/type/device_type/id/+/evt/event_id/fmt/format_string
Publishingdevice events
An application can publish events asif they camefrom any registered device.
- Publish to topic iot-2/type/device_type/id/device_id/evt/event_id/fmt/format_string
Fox example:
App end subscribe topic:
String topic = "iot-2/type/" + MqttUtil.DEFAULT_DEVICE_TYPE + "/id/+/evt/"+ MqttUtil.DEFAULT_EVENT_ID + "/fmt/json";
subscribetopic: iot-2/type/devicecbs1/id/+/evt/eid/fmt/json
App end onPublish Listener topic:
Pattern pattern = Pattern.compile("iot-2/type/"
+MqttUtil.DEFAULT_DEVICE_TYPE + "/id/(.+)/evt/"
+MqttUtil.DEFAULT_EVENT_ID + "/fmt/json");
mqtt onPublic-----------:iot-2/type/devicecbs1/id/cbsdevicea/evt/eid/fmt/json
//Publish device events tothe app
//iot-2/evt/<event-id>/fmt/<format>
handler.publish("iot-2/evt/"+ MqttUtil.DEFAULT_EVENT_ID
+"/fmt/json", jsonObj.toString(), false, 0);
That means, the device and app to communicate only by “evt”!!
Note:
wildcard character only available in subscribe topic!
Publish topic is not allowed!
2.App send message to Device/Sensor（订阅端在device，发布端在app）：
Subscribingto device commands
An application can subscribe tocommands beingsent to one or more devices.
- Subscribe to topic： iot-2/type/device_type/id/device_id/cmd/command_id/fmt/format_string
Note
The MQTT “any” wildcard character(+) may be used for any of the following components if you want to subscribe tomore than one type of event, or events from more than a single device.
- device_type
- device_id
- cmd_id
- format_string
Publishingdevice commands
An application can publish a commandto anyregistered device.
- Publish to topic iot-2/type/device_type/id/device_id/cmd/command_id/fmt/format_string
//Subscribe the Command events
//iot-2/cmd/<cmd-type>/fmt/<format-id>
handler.subscribe("iot-2/cmd/"+ MqttUtil.DEFAULT_CMD_ID + "/fmt/json",0);
references：
https://docs.internetofthings.ibmcloud.com/messaging/applications.html
https://docs.internetofthings.ibmcloud.com/messaging/devices.html