Android : How to send String[] As value of HashMap to REST From Android(Java)

I am trying to send a HashMap to Magento REST API From Android. The rest contain a array element as showing below.

 [{"id":"26",
"label":"",
"position":"1",
"exclude":"0",
 "url":"http:\/\/localhost\/magento\/media\/catalog\/product\/6\/1\/61UROlGlryL._UL1500_.jpg_20.jpg",
"types":[]}]  

I tried to send the data using HttpPost As showing below.

    Map<String,String> productimages = new HashMap<String, String>();

    productimages.put("file_mime_type", mime);
    productimages.put("file_content", encodedImage);
    productimages.put("file_name", pictureName);

    String[] datas = {"image","small_image","thumbnail"};
    productimages.put("types", datas.toString);

    StringEntity productimages_entity = new StringEntity(productimages_json,HTTP.UTF_8);
    HttpPost httppost_img = new HttpPost(URL_PRODUCTS+"/6/images");
    httppost_img.setHeader("Content-Type", "application/json");
    httppost_img.setHeader("Accept", "application/json");
    httppost_img.setEntity(productimages_entity);
    Log.d("inserted", "");
    HttpResponse response_img = client.execute(targetHost, httppost_img,
                                localContext);

All the data rather than "types":[ ] is hitting the web service. When send the data as single string like productimages.put("types", "image"); it hit the web service Successfully But I need to send more than one value.Also I tried the following but no result.

 Map<String,String[]> productimages = new HashMap<String, String[]>();
 String[] datas = {"image","small_image","thumbnail"};
 productimages.put("types", datas);

How I can send the String[] values with the single key to REST Web Service.Anyone please help me to solve this.