NanoHTTPD how to present variable from app

I play NanoHTTPD and WebServer based on it. To update any object in my code (application) I can use GET/POST method. But how can I create dynamic pages? For example I have html page on disc and it should present current temperature:

<html>
  <head>
    <title>My page</title>
  </head>

  <body>

    <p style="text-align: center">Temperature: [temperature variable] </p>

  </body>

</html>

How can I pass "variable temperature" from my application based on NanoHTTPD to html file and present it in browser?

Solution

You have to read the template from your disk, and replace the [temperature variable] substring with the value you want to include.

To read the file, you can use the Files class:

byte[] data = Files.readAllBytes(Paths.get("mytemplpate.html"));
String templ = new String(data, StandardCharsets.UTF_8);

To insert your temperature:

double temperature = 22.3;
String html = templ.replace("[temperature variable]", Double.toString(temperature));

And finally to send this as the response with NanoHTTPD:

return new NanoHTTPD.Response(html);

The complete program:

Foreword: Exceptions are not handled, this is just for demonstration purposes.

public class TemperatureServer extends NanoHTTPD {
    // Loaded and cached html template
    private static String templ;

    // Value of this variable will be included and sent in the response
    private static double temperature;

    public TemperatureServer () {
        super(8080);
    }

    @Override
    public Response serve(IHTTPSession session) {
        String html = templ.replace("[temperature variable]",
            Double.toString(temperature));
        return new NanoHTTPD.Response(html);
    }

    public static void main(String[] args) throws Exception {
        byte[] data = Files.readAllBytes(Paths.get("mytemplpate.html"));
        templ = new String(data, StandardCharsets.UTF_8);

        ServerRunner.run(TemperatureServer.class);
    }
}

For more advanced examples check out the Samples package of the NanoHttpd Github site.