Broker Architecture Pattern | Nagacharan Teja Tangirala

Client and server talk to each other to carry out transactions. However, the implementation of the server can be in an entirely different language with an incompatible API. Broker pattern helps to enable communication between such diverse client and server implementations. Further, it decouples the client and server, allowing good extensibility even during runtime.

A very dumb broker implementation is demo’d here, the real implementations are typically complex.

Phone is a client that wants to access the weather server to get latest temperature:

class Phone {

    ...
    private double temperature;
    private Location location;
    private WeatherService weatherService;
    ...

    public void getTemperature() {
        this.temparature = this.weatherService.getTemperature(this.location);
    }
    ...
}

A simple WeatherService can be:

class WeatherService {

    ...
    double getTemperature(Location location) {
        double temperature = 0;
        // Some logic to get the latest temperature data and update it.
        return temperature;
    }
    ...
}

Such an implementation is tightly coupled. Broker pattern allows us to decouple this.

A simple broker will contain a list of services and returns the requested service to the client.

class Broker {

    ...
    private WeatherService weatherService;
    ...

    ...
    double getTemperature(Location location) {
        if (this.weatherService != null) {
            return this.weatherService.getTemperature(location);
        } else {
            return ServiceNotFoundException("Weather service is not available");
        }
    }
    ...
}

Client, instead of directly contacting the WeatherService directly, will talk to the Broker. The modified Client will now look like this:

class Phone {

    ...
    private double temperature;
    private Location location;
    private Broker broker;
    ...

    ...
    public void getTemperature() {
        this.temparature = this.broker.getTemperature(this.location);
    }
    ...
}

This is how Broker pattern sits in between Client and Server and helps to decouple them. Expansion is also easier with this approach.

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