Question

i am new to jsp and just built my first application. I am following a book. The book used a code

<form name="addForm" action="ShoppingServlet" method="post">
    <input type="hidden" name="do_this" value="add">

    Book:
    <select name="book">                   

    <%  
        //Scriplet2: copy the booklist to the selection control
        for (int i=0; i<bookList.size(); i++) {

            out.println("<option>" + bookList.get(i) + "</option>");

         } //end of for
     %>                   
     </select>

     Quantity:<input type="text" name="qty" size="3" value="1">               
     <input type="submit" value="Add to Cart">

</form>

and in the servlet the code is

else if(do_This.equals("add")) {

    boolean found = false;
    Book aBook = getBook(request);
    if (shopList == null) { // the shopping cart is empty

        shopList = new ArrayList<Book>();
        shopList.add(aBook);

    } else {...  }// update the #copies if the book is already there

private Book getBook(HttpServletRequest request) {

    String myBook = request.getParameter("book");   //confusion
    int n = myBook.indexOf('$');
    String title = myBook.substring(0, n);
    String price = myBook.substring(n + 1);
    String quantity = request.getParameter("qty");  //confusion
    return new Book(title, Float.parseFloat(price), Integer.parseInt(quantity));

} //end of getBook()

My question is when i click on add Add to Cart button then in the servelt at line String myBook = request.getParameter("book"); i get book as a parameter but in my jsp i didn’t say that request.setAttribute("book", "book"), same for request.getParameter("qty");. How my servlet is receiving these request parameters without setting it in jsp code?
Thanks

Answer 1

You get that parameter because in your form you have this:

<select name="book">

The user never does a request.setParameter (such a method is not even defined)

You can also set a parameter by invoking the servlet with a query string. Something like:

http://localhost:8080/ShoppingServlet?name=abcd&age=20

The above will create two request parameters named abc and age which you can access using request.getParameter