Can a Servlet Preprocess a JSP Page Load Without a Form Submission?

Servlet Preprocessing for JSP Page Load

You may encounter a scenario where you want to display results from a database in an HTML table directly when a JSP page loads. This raises the question of whether it's possible to invoke a servlet from a JSP file without employing a traditional HTML form.

Preprocessing with Servlet's doGet() Method

The answer is affirmative. By utilizing the doGet() method of a servlet, you can preprocess a request and subsequently forward it to the JSP. This involves redirecting links and browser address bars to the servlet's URL instead of the JSP's URL.

Example Implementation

Consider the following code snippet:

@WebServlet("/products")
public class ProductsServlet extends HttpServlet {

    @EJB
    private ProductService productService;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Product> products = productService.list();
        request.setAttribute("products", products);
        request.getRequestDispatcher("/WEB-INF/products.jsp").forward(request, response);
    }

}

In the JSP file (/WEB-INF/products.jsp):

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
...
<table>
    <c:forEach items="${products}" var="product">
        <tr>
            <td>${product.name}</td>
            <td>${product.description}</td>
            <td>${product.price}</td>
        </tr>
    </c:forEach>
</table>

Considerations

• Place the JSP file within the /WEB-INF folder to prevent direct access by users.
• Servlet 3.0 (Tomcat 7, etc.) is required for @WebServlet annotation support. Refer to @WebServlet annotation with Tomcat 7 for more information.
• For Servlet versions prior to 3.0, manual servlet registration in web.xml is necessary.

Additional Resources

• Servlets wiki page
• doGet and doPost in Servlets
• How to avoid Java code in JSP
• Servlet returns "HTTP Status 404 The requested resource (/servlet) is not available"

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