An HTML form can only submit to one place:

<form action="myServlet" method="post">

...

    <input type="submit" value="Add to Cart">
    <input type="submit" value="Remove from Cart">

</form>

You could have two forms in the HTML rendered by the ReviewShoppingCart,
 with one button in each and different action paths.

<form action="AddToCart" method="post">

...

    <input type="submit" value="Add to Cart">

</form>

<form action="RemoveFromCart" method="post">

...

    <input type="submit" value="Remove from Cart">

</form>

But I would combine your AddToShoppingCart and RemoveFromCart servlets
into a single servlet and choose your action based on the button that
was pressed:

<form action="EditShoppingCart" method="post">

...

    <input name="action" type="submit" value="Add to Cart">
    <input name="action" type="submit" value="Remove from Cart">

</form>

This will add an additional parameter to the request called "action"
that will be set to "Add to Cart" or "Remove from Cart".

Then in your servlet:

    String action = request.getParameter("action");

    if ("Add to Cart".equals(action)) {
        ...
    }
    else if ("Add to Cart".equals(action)) {
        ...
    }
    else {
        ...
    }