Android URL和HTTP Post错误

当我尝试使用HTTP POST将数据传递给服务器时，遇到了问题。我想将这些数据插入到数据库中。但是，当我测试时，错误显示为“很抱歉，...已停止工作。”

TestActivity.java

public class TestActivity extends AppCompatActivity {
    ArrayList cartList;
    String URL_SEND;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);
        cartList = new ArrayList<>();
        URL_SEND = "http://192.168.56.1/api.php";
        new SendOrder().execute();
    }
    class SendOrder extends AsyncTask {
        @Override
        protected Void doInBackground(Void... params) {
            Cart cart1 = new Cart("1", 3);
            cartList.add(cart1);
            Cart cart2 = new Cart("2", 2);
            cartList.add(cart2);
            try {
                URL url = new URL(URL_SEND);
                HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setRequestProperty("Content-Type", "application/json");
                httpURLConnection.connect();
                JSONObject jsonObject = new JSONObject();
                jsonObject.put("idUser", "1");
                jsonObject.put("total", 50000);
                jsonObject.put("cartArray", new JSONArray(cartList));
                jsonObject.put("key", "12345");
                OutputStreamWriter writer = new OutputStreamWriter(httpURLConnection.getOutputStream());
                writer.write(jsonObject.toString());
                writer.flush();
                Toast.makeText(TestActivity.this, "订单成功", Toast.LENGTH_LONG).show();
                cartList.clear();
            } catch (Exception e) {
                Toast.makeText(TestActivity.this, "服务器错误", Toast.LENGTH_LONG).show();
            }
            return null;
        }
    }
}

Cart.java

public class Cart {
    private String idMenu;
    private int quantity = 0;
    public Cart() {
    }
    public Cart(String idMenu, int quantity){
        this.idMenu = idMenu;
        this.quantity = quantity;
    }
    public String getIdMenu(){
        return idMenu;
    }
    public void setIdMenu(String idMenu) {
        this.idMenu = idMenu;
    }
    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
}

api.php

prepare("INSERT INTO order(user_id, total, status_order, time)
            VALUES(:idUser, :total, :status, :waktu)");
        $res = $sth->execute(array(
            'idUser' => $user_id,
            'total' => $total,
            'status' => $status,
            'waktu' => date()
        ));
        $id = $dbh->lastInsertId();
        foreach ($cartArray as $cart) {
            $idProduct = $cart->idMenu;
            $qty = $cart->quantity;
            $sth = $dbh->prepare('INSERT INTO order_detail(id_order, id_product, qty) VALUES (:idOrder, :idProduct, :qty)');
            $res = $sth->execute(array(
                'idOrder' => $id,
                'idProduct' => $idProduct,
                'qty' => $qty
            ));
        }
    }
}
?>

似乎URL本身有问题。当我只运行URL url = new URL(URL_SEND);时，出现了相同的错误。我不知道为什么这段代码不起作用。

编辑

这是我得到的错误。

FATAL EXCEPTION: AsyncTask #1
Process: com.catering.catering, PID: 5219
java.lang.RuntimeException: An error occurred while executing doInBackground()
    at android.os.AsyncTask$3.done(AsyncTask.java:309)
    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
    at java.lang.Thread.run(Thread.java:818)
Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
    at android.os.Handler.(Handler.java:200)
    at android.os.Handler.(Handler.java:114)
    at android.widget.Toast$TN.(Toast.java:345)
    at android.widget.Toast.(Toast.java:101)
    at android.widget.Toast.makeText(Toast.java:259)
    at com.catering.catering.TestActivity$SendOrder.doInBackground(TestActivity.java:90)
    at com.catering.catering.TestActivity$SendOrder.doInBackground(TestActivity.java:57)
    at android.os.AsyncTask$2.call(AsyncTask.java:295)
    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
    at java.lang.Thread.run(Thread.java:818)