Gson转炉厂改造2。 序列化/反序列化中的不同类型

I'm working with wordpress post metas and rest api, i've exposed to rest a meta field called "picture_collection" wich store data as an array of integers where every number represents the ID of an attachment. I've then modified the response when interrogating the api to give me a list of links instead of the attachment ids, like this:

    function get_pic_coll ($object, $field_name, $request) {
        include_once dirname(__FILE__) . '/attach_coll.php';
        $pic_coll = get_post_meta ($object['id'], $field_name, true);
        $json_coll = array();
        if($pic_coll != null || !empty($pic_coll)){
            foreach ($pic_coll as $pic){
                $media_id = $pic;
                $link_med = wp_get_attachment_image_src($media_id, 'medium');
                $link_full = wp_get_attachment_image_src($media_id, 'full');
                $medium_size = $link_med[0];
                $full_size = $link_full[0];
                $obj = new attach_coll($media_id, $medium_size, $full_size);
                $element = $obj->return_coll_object();
                $json_coll[] = $element;
            }
            return $json_coll;
        }
    }

while the attach_coll object is:

class attach_coll{
public function __construct($media_id, $medium_url, $orig_url){
    $this->attach_id = $media_id;
    $this->medium_size_pic = $medium_url;
    $this->full_size_pic = $orig_url;
}

private $attach_id;
private $medium_size_pic;
private $full_size_pic;

public function get_media_id(){
    return $this->attach_id;
}
public function get_medium_pic(){
    return $this->medium_size_pic;
}
public function get_orig_pic(){
    return $this->full_size_pic;
}
public function return_coll_object(){
    $ret_coll = array(
            "ID"     => $this->get_media_id(),
            "medium" => $this->get_medium_pic(),
            "full"   => $this->get_orig_pic()
    );
    return $ret_coll;
}

}

Java side the things goes like this: 1)the user make a picture and upload her, he receive in exchange the ID of the attachment that is stored inside an Integers ArrayList. 2)when he has done the program update the post_meta passing to the api the entire list. 3)the program receive the response as a json containing the whole post with my custom field, it looks like this:

{...
   "id":"someValue",
   "title":"myTitle",
   "pic_collection":[ {'ID':'picID','mediumSizePic':'someUrl', 'FullSizePic':'SomeOtherUrl},{...}],

The php code works well as i see from the ResponseBody the json i was expecting, the problem is that i'm getting an error 'gson expected a Integer and found an Object' that is logical because the pojo is defined like:

@SerializedName("pic_collection")
private List<Integer> idList = new ArrayList<Integer>();
public void setList(List<Integer> list){
this.idList=list;
}

I tried to change my list to:

List<PicCollection> picList = new ArrayList<PicCollection>();
public class PicCollection{
@SerializedName("ID")
private int picId;
@SerializedName("medium_size")
private String medSizeUrl;
@SerializedName("full_size")
private String fullSizeUrl;
Getters and Setters
}

But that just complicated everything up and didn't resolved the problem as i'm still having a the same gson error 'ID expecting an int but found an object' and no links returned at all. A glimpse on the code to set the id's:

iterator=idList.iterator;
while(iterator.hasNext()){
 FotoCollection fc = new FotoCollection();
 fc.ID = iterator.next

What can i do to resove the problem? I need a custom converter?

I just created 2 objects: One for the request and one for the response.