How to Call Servlets from JSP Files on Page Load?

Calling Servlets from JSP Files on Page Load

Introduction

Accessing data and implementing complex logic can be achieved with Servlets, which are utilized in Java web applications to process requests and responses dynamically. Developers may encounter the need to initiate a servlet's functionality directly from a JSP file during page load. This article provides a comprehensive solution to this challenge.

Processing Requests Before Page Load

To execute a servlet before the JSP page is rendered, the doGet() method of the servlet can be employed. This method serves to preprocess requests and forward them to the JSP, effectively decoupling processing from presentation. By redirecting links and browser addresses to the servlet's URL instead of the JSP's, the desired functionality can be achieved.

A Practical Example

In this example, a servlet named ProductsServlet is used to retrieve product data from a database and forward it to the products.jsp JSP file for display. The servlet is annotated with @WebServlet("/products"), indicating that its URL pattern is "/products".

@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);
    }
}

Access Data in JSP

Within the products.jsp file, the list of products is rendered using Java Server Pages Standard Tag Library (JSTL) and Expression Language (EL).

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
...
<table border="1">
    <c:forEach items="${products}" var="product">
        <tr>
            <td>${product.name}</td>
            <td>${product.description}</td>
            <td>${product.price}</td>
        </tr>
    </c:forEach>
</table>

Considerations

It is crucial to ensure that the JSP file is placed inside the /WEB-INF folder to prevent direct access without calling the servlet. Additionally, note that the @WebServlet annotation is only available in Servlet 3.0 and later, and if using an older version, registration of the servlet through the web.xml file is necessary.

Benefits of Using Servlets for Page Load Processing

• Improved code organization
• Separation of concerns
• Increased flexibility and reusability of components

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