String jsonString= smsMMs.getMmsContent();
//jsonString转成json对象
JSONObject mmsContentObj = JSONObject.parseObject(jsonString);
从json对象中获取json数组
JSONArray frames = mmsContentObj.getJSONArray("frames");
String[] framesIndexs = new String[frames.size()];
for (int i = 0; i < frames.size(); i++) {
String index = frames.getJSONObject(i).getString("index");
framesIndexs[i] = index;
}