android.java

@Override
public boolean execute(String action, JSONArray args, CallbackContext callbackContext) throws JSONException {
    if ("echo".equals(action)) {
        this.echo(args.getString(0), callbackContext);
        return true;
    }
    return false;  // Returning false results in a "MethodNotFound" error.
}

public void echo(String echo, CallbackContext callbackContext) {
    final PluginResult result;
    if (echo != null && echo.length() > 0) {
        result = new PluginResult(PluginResult.Status.OK, echo);
    } else {
        result = new PluginResult(PluginResult.Status.ERROR);
    }
    
    callbackContext.sendPluginResult(result);
}