Add Json encoded data to AWS DynamoDB

I have figured out the solution.
I think this may help some one in future.
I followed the Marshaler method.

require('aws/aws-autoloader.php');
use Aws\DynamoDb\DynamoDbClient;
use Aws\DynamoDb\Marshaler;

// --------------------------------------------------------------------

$feed_url = 'http://localhost/json/j_xml.xml'; 
$xml_data = simplexml_load_file($feed_url);

// -------------------------------------------------------------------- 

$i=0; 
$results    =   array('return' => true,'message' => 'success','details' => array(),'response'=>array());
$AWS_ACCESS_KEY_ID  = '******************';
$AWS_SECRET_ACCESS_KEY = '*******************';
$AWS_REGION = '<region-code>';

$client = DynamoDbClient::factory(array(
            'version'     => '2012-08-10',
            'credentials' => array(
            'key'    =>  $AWS_ACCESS_KEY_ID,
            'secret' => $AWS_SECRET_ACCESS_KEY,
            ),
            'region' => $AWS_REGION
            ));

$marshaler = new Marshaler();
foreach($xml_data->channel->item as $ritem) { 
$e_wp                           = $ritem->children("wp", true);
$e_author                       = $ritem->children("dc", true);
$e_content                      = $ritem->children("content", true);
// --------------------------------------  
if((string)$e_wp->status =='publish') {
$post_id                        = (string)$ritem->guid; 
$post_id                        = explode('=', $post_id);
$content['ArticleID']           = $post_id[1]; 
$content['article_title']       = (string)$ritem->title; 
$content['article_cat_slug']    = 'News'.$post_id[1]; 
$content['article_mob_title']   = (string)$ritem->title; 
$content['article_category']    = (string)$ritem->category;
$content['article_pub_date']    = (string)$e_wp->post_date;
$content['article_description'] = (string)$ritem->description; 
$content['article_content']     = (string)$e_content->encoded; 
$content['article_author']      = (string)$e_author->creator; 
/* DynamoDB doesnot accept empty string
$content['article_seo_desc']    = ''; 
$content['article_seo_tags']    = ''; 
$content['article_fb_title']    = ''; 
$content['article_fb_desc']     = ''; 
$content['article_twitter']     = '';
*/
$content['article_create_date'] = (string)$e_wp->post_date_gmt;
$content['article_status']      = (string)$e_wp->status; 
$content = array_filter($content);
$json =  json_encode($content,JSON_PRETTY_PRINT);
$response = $client->putItem([
    'TableName' => 'Article',
    'Item'      => $marshaler->marshalJson($json)
]);

}
array_push($results['details'],$content);
array_push($results['response'],$response);

}