如何在参数Volley Post Request中发送多个对象String？

Question

我必须在Volley Post请求的参数函数中向服务器发送2个对象，但是我不知道如何向服务器发送数据？

我尝试搜索，但未找到结果。

这是我发送到服务器的对象

{
    "customer_email": "jawadsaqib6@gmail.com",
    "customer_phone": "03342234332",
    "shipping": {
        "first_name": "saham",
        "last_name": "nadeem",
        "address_1": "asdadjjslajslldjslds",
        "address_2": "",
        "city": "Islamabad",
        "zip": "44000",
        "country": "US",
        "state": "AL"
    },
    "products": [
        {
            "product_id": 25,
            "qty": 2,
            "options": [
                {
                    "16": 61
                }
            ]
        }
    ]
}

我做对象并尝试发送数据

Cart_CheckOut.Billing billing;

private void checkOut_Order() {

        StringRequest stringRequest = new StringRequest (Request.Method.POST, CHECKOUT_URL,  new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {

                try{
                    JSONObject jsonObject= new JSONObject(String.valueOf(response));
                    String msg = jsonObject.getString("message");


                }
                catch (JSONException e){
                    Toast.makeText(ShippingInfo.this, "Exception", Toast.LENGTH_SHORT).show();
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
            }
        })

        {
            @Override
            protected Map<String, String> getParams() {
                Map<String, String> hashMap = new HashMap<>();

                hashMap.put("customer_email", "");
                hashMap.put("customer_phone", "");
                hashMap.put("billing",billing);
                return hashMap;
            }

        };
        RequestQueue requestQueue = Volley.newRequestQueue(this);
        requestQueue.add(stringRequest);
    }

我不知道如何将对象发送到服务器。