use Yiisoft\DataResponse\DataResponseFactory;

/**
 * @var Psr\Http\Message\ResponseFactoryInterface $responseFactory
 */

$factory = new DataResponseFactory($responseFactory);
$dataResponse = $factory->createResponse('test');
$dataResponse
    ->getBody()
    ->rewind();

echo $dataResponse
    ->getBody()
    ->getContents(); // "test"

use Yiisoft\DataResponse\DataResponseFactory;
use Yiisoft\DataResponse\Formatter\JsonDataResponseFormatter;

/**
 * @var Psr\Http\Message\ResponseFactoryInterface $responseFactory
 */

$factory = new DataResponseFactory($responseFactory);
$dataResponse = $factory->createResponse('test');
$dataResponse = $dataResponse->withResponseFormatter(new JsonDataResponseFormatter());
$dataResponse
    ->getBody()
    ->rewind();

echo $dataResponse->getHeader('Content-Type'); // ["application/json; charset=UTF-8"]
echo $dataResponse
    ->getBody()
    ->getContents(); // "test"

use Yiisoft\DataResponse\Middleware\FormatDataResponse;
use Yiisoft\DataResponse\Formatter\JsonDataResponseFormatter;

$middleware = (new FormatDataResponse(new JsonDataResponseFormatter()));
//$middleware->process($request, $handler);

use Yiisoft\DataResponse\Formatter\HtmlDataResponseFormatter;
use Yiisoft\DataResponse\Formatter\XmlDataResponseFormatter;
use Yiisoft\DataResponse\Formatter\JsonDataResponseFormatter;
use Yiisoft\DataResponse\Middleware\ContentNegotiator;

$middleware = new ContentNegotiator([
    'text/html' => new HtmlDataResponseFormatter(),
    'application/xml' => new XmlDataResponseFormatter(),
    'application/json' => new JsonDataResponseFormatter(),
]);

$middleware->withContentFormatters([
    'application/xml' => new XmlDataResponseFormatter(),
    'application/json' => new JsonDataResponseFormatter(),
]);