How does the mqtt server built with emqx forward data and save it to the cloud database?

Record your own solutions to this problem ！

One 、 Technical principle

Create a new resource interface to forward the specified data , Then set rules for filtering subject messages in the rule engine , Filter out the messages of the topic you need , Set forwarded http Interface （URL）,http Request to select POST or GET request , The requirement is to write servlet Interface with doPost()、doGet() Methods corresponding to the .servlet The logic in the interface is to add, delete, modify and query the database , Of course servlet The interface is also deployed in the cloud ！

Two 、 Implementation steps

1、 Create a new resource interface ：

open EMQX The background of , Create a new resource , Resource type selection webhook, resources ID You can modify it yourself or not , Fill in url, Here I use tomcat Server deployment servlet Interface , The port is 8080, If you use other servers to deploy , Please fill in the port of the server ！

2、 Set the subject message filtering rules and configure the forwarding resource interface ：

Rules of choice , Click to create a new rule . Here you need to write a filter for topic messages SQL sentence .

there payload It's a message object , Every message received by the topic has the following properties , The data we transmit is payload in , It is json Format , So when uploading your data, you'd better also use json Format .

{
    
  "username": "u_emqx",
  "topic": "smartHome",
  "timestamp": 1614515277516,
  "qos": 1,
  "publish_received_at": 1614515277516,
  "peerhost": "127.0.0.1",
  "payload": "{\"t\":\"light\",\"light\":\"20\"}",
  "node": "[email protected]",
  "metadata": {
    
    "rule_id": "test_rule4a19e8ea"
  },
  "id": "5BC64A199D064F44072000AB80000",
  "flags": {
    
    "sys": true,
    "event": true
  },
  "clientid": "c_emqx"
}

my payload The first data is the sensor type , The second data is the real data collected by the sensor , You can design according to your own situation , Then click test , If the message sent meets the setting SQL sentence , You can see the output result .

After finding the message that conforms to the rules , Add a corresponding action , Type select to send data to web service , Associate resources and select the resource interface you just created , Just leave the message content template blank by default ！

That's it MQTT The server forwards data to the specified interface , The next step is to write servlet interface program

3、 To write servlet interface program

It may take a little bit here JavaWeb Basics , Will use doPost() and doGet() The method is almost done , The rest is the addition, deletion, modification and query of the database .

If you select POST request , Then in doPost() Get from method MQTT Data forwarded by the server , Because with http Protocol transfer , The data will be passed out in the form of parameters ,POST The requested parameters are obtained in the request body , Get is json Formatted data ;

If you choose GET request , It's just doGet() Method , Data is also passed in the form of parameters , But it is transmitted in clear text , So directly in doGet() Method, just call the function to get the request parameters .

Because there are many types of sensors , Need to match multiple servlet interface program , So you need to be in web.xml Next, set the mapping relationship , For example, enter... In the address field ：http://ip:8080/ Project name /light, It will match you LightServlet Deal with your request , Because I've put light and LightServlet The binding . Did you learn JavaWeb You should know this .

4、 Deploy in the cloud servlet Interface

Because I haven't learned much Linux, Therefore, it is suggested that you can use the pagoda panel to install tomcat The server and MySQL database , About the installation of pagoda panels , Baidu has many ！

Install well tomcat After the server , find tomcat In the catalog webapp Catalog , And then put what's written Servlet Interface upload here , It will automatically decompress ！

stay server.xml Middle configuration , As for why , There are three kinds on Baidu tomcat How to deploy the project ！

5、 test servlet Interface

stay EMQX The test function is provided in the tools menu in the background of , Click on websocket, Connect mqtt After the server , Enter the simulated message , Click Send , You can see mysql Two rows of data are added to the light intensity table in the data , prove servlet Interface is ok Of .

This is just to add data , Other queries , The modification function is also implemented in this way . That's my personal right EMQX Just a little insight into forwarding data to the database ！

My own functions are as follows ：

The source code is also for you , Interested friends can study it ！
Address ：https://github.com/ldcowq/smartHome