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https://github.com/WebThingsIO/webthing-java

Java implementation of a Web Thing server
https://github.com/WebThingsIO/webthing-java

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Java implementation of a Web Thing server

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# webthing



[![Build Status](https://github.com/WebThingsIO/webthing-java/workflows/Java%20package/badge.svg)](https://github.com/WebThingsIO/webthing-java/workflows/Java%20package)

[![Maven](https://img.shields.io/maven-central/v/io.webthings/webthing.svg)](https://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22io.webthings%22%20AND%20a%3A%22webthing%22)

[![license](https://img.shields.io/badge/license-MPL--2.0-blue.svg)](LICENSE)



Implementation of an HTTP [Web Thing](https://webthings.io/api).



# Using



## Maven



Add the following dependency to your project:



```xml



    

        io.webthings

        webthing

        0.15.0

    



```



## Gradle



Add the following dependency to your project:



```gradle

dependencies {

    runtime(

        [group: 'io.webthings', name: 'webthing', version: '0.15.0'],

    )

}

```



## Android Studio



- Open File → Project Structure

- Select the module you want to add this as a dependency to

- Go to the "Dependencies" tab

- Click green "+" button

- Select "Library dependency"

- Enter `io.webthings:webthing` in the search bar and search

- Select the package in the result and confirm with "OK"

- Click "OK" in the Project Structure dialog



# Example



In this example we will set up a dimmable light and a humidity sensor (both using fake data, of course). Both working examples can be found in [here](https://github.com/WebThingsIO/webthing-java/tree/master/src/main/java/io/webthings/webthing/example).



## Dimmable Light



Imagine you have a dimmable light that you want to expose via the web of things API. The light can be turned on/off and the brightness can be set from 0% to 100%. Besides the name, description, and type, a [`Light`](https://webthings.io/schemas/#Light) is required to expose two properties:

* `on`: the state of the light, whether it is turned on or off

    * Setting this property via a `PUT {"on": true/false}` call to the REST API toggles the light.

* `brightness`: the brightness level of the light from 0-100%

    * Setting this property via a PUT call to the REST API sets the brightness level of this light.



First we create a new Thing:



```java

Thing light = new Thing("urn:dev:ops:my-lamp-1234",

                        "My Lamp",

                        new JSONArray(Arrays.asList("OnOffSwitch", "Light")),

                        "A web connected lamp");

```



Now we can add the required properties.



The **`on`** property reports and sets the on/off state of the light. For this, we need to have a `Value` object which holds the actual state and also a method to turn the light on/off. For our purposes, we just want to log the new state if the light is switched on/off.



```java

JSONObject onDescription = new JSONObject();

onDescription.put("@type", "OnOffProperty");

onDescription.put("title", "On/Off");

onDescription.put("type", "boolean");

onDescription.put("description", "Whether the lamp is turned on");



Value on = new Value<>(true,

                                // Here, you could send a signal to

                                // the GPIO that switches the lamp

                                // off

                                v -> System.out.printf(

                                        "On-State is now %s\n",

                                        v));



light.addProperty(new Property(light, "on", on, onDescription));

```



The **`brightness`** property reports the brightness level of the light and sets the level. Like before, instead of actually setting the level of a light, we just log the level.



```java

JSONObject brightnessDescription = new JSONObject();

brightnessDescription.put("@type", "BrightnessProperty");

brightnessDescription.put("title", "Brightness");

brightnessDescription.put("type", "number");

brightnessDescription.put("description",

                          "The level of light from 0-100");

brightnessDescription.put("minimum", 0);

brightnessDescription.put("maximum", 100);

brightnessDescription.put("unit", "percent");



Value level = new Value<>(0.0,

                                  // Here, you could send a signal

                                  // to the GPIO that controls the

                                  // brightness

                                  l -> System.out.printf(

                                          "Brightness is now %s\n",

                                          l));



light.addProperty(new Property(light, "level", level, brightnessDescription));

```



Now we can add our newly created thing to the server and start it:



```java

try {

    // If adding more than one thing, use MultipleThings() with a name.

    // In the single thing case, the thing's name will be broadcast.

    WebThingServer server = new WebThingServer(new SingleThing(light), 8888);



    Runtime.getRuntime().addShutdownHook(new Thread() {

        public void run() {

            server.stop();

        }

    });



    server.start(false);

} catch (IOException e) {

    System.out.println(e);

    System.exit(1);

}

```



This will start the server, making the light available via the WoT REST API and announcing it as a discoverable resource on your local network via mDNS.



## Sensor



Let's now also connect a humidity sensor to the server we set up for our light.



A [`MultiLevelSensor`](https://webthings.io/schemas/#MultiLevelSensor) (a sensor that returns a level instead of just on/off) has one required property (besides the name, type, and optional description): **`level`**. We want to monitor this property and get notified if the value changes.



First we create a new Thing:



```java

Thing sensor = new Thing("urn:dev:ops:my-humidity-sensor-1234",

                         "My Humidity Sensor",

                         new JSONArray(Arrays.asList("MultiLevelSensor")),

                         "A web connected humidity sensor");

```



Then we create and add the appropriate property:

* `level`: tells us what the sensor is actually reading

    * Contrary to the light, the value cannot be set via an API call, as it wouldn't make much sense, to SET what a sensor is reading. Therefore, we are creating a *readOnly* property.



    ```java

    JSONObject levelDescription = new JSONObject();

    levelDescription.put("@type", "LevelProperty");

    levelDescription.put("title", "Humidity");

    levelDescription.put("type", "number");

    levelDescription.put("description", "The current humidity in %");

    levelDescription.put("minimum", 0);

    levelDescription.put("maximum", 100);

    levelDescription.put("unit", "percent");

    levelDescription.put("readOnly", true);



    this.level = new Value<>(0.0);



    sensor.addProperty(new Property(sensor, "level", level, levelDescription));

    ```



Now we have a sensor that constantly reports 0%. To make it usable, we need a thread or some kind of input when the sensor has a new reading available. For this purpose we start a thread that queries the physical sensor every few seconds. For our purposes, it just calls a fake method.



```java

// Start a thread that polls the sensor reading every 3 seconds

new Thread(()->{

    while(true){

        try {

            Thread.sleep(3000);

            // Updates the underlying value, which in turn notifies all

            // listeners

            this.level.notifyOfExternalUpdate(readFromGPIO());

        } catch (InterruptedException e) {

            throw new IllegalStateException(e);

        }

    }

}).start();

```



This will update our `Value` object with the sensor readings via the `this.level.notifyOfExternalUpdate(readFromGPIO());` call. The `Value` object now notifies the property and the thing that the value has changed, which in turn notifies all websocket listeners.



# Adding to Gateway



To add your web thing to the WebThings Gateway, install the "Web Thing" add-on and follow the instructions [here](https://github.com/WebThingsIO/thing-url-adapter#readme).