java - 从 Servlet 传递 JSP 中的数据：技巧

Question

我目前正在使用 JSP、JSTL、Servlet 等。我有一个问题。我不明白这种情况。

案例1（这个案例非常棒，在JSP文件中显示数据库记录）：

小服务程序

@WebServlet("/books")
public class IndexController extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ArrayList<Book> books = new BookDAO().getAllBooks();
        request.setAttribute("books", books);
        request.getRequestDispatcher("index.jsp").forward(request, response);
    }

JSP

<c:forEach items="${books}" var="book">
        ${book}
    </c:forEach>

案例2（这个案例不行，JSP文件中不显示数据库记录）：

小服务程序

@WebServlet("/")
public class IndexController extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ArrayList<Book> books = new BookDAO().getAllBooks();
        request.setAttribute("books", books);
        request.getRequestDispatcher("index.jsp").forward(request, response);
    }

JSP 文件同上。

案例 1：我尝试 localhost/AppName/books => 它有效。

案例 2：我尝试 localhost/AppName/ => 它不起作用

我想在 localhost/AppName 页面显示数据库记录。我该怎么办？