 <p>I believe you want your MainHash with same key in MainArray.</p> <p>So, you can try, </p> <pre><code> for (String item : array_items) { entity.addPart("MainHash[MyArray][]", new StringBody(item)); } </code></pre> <p>It will create,</p> <pre><code>[one,two,three] </code></pre> <p>as an array.</p>