在页面加载时从JSP文件调用servlet [英] Calling a servlet from JSP file on page load

问题描述

我可以在不使用HTML表单的情况下从JSP文件调用servlet吗？

Can I call a servlet from JSP file without using a HTML form?

例如，在页面加载期间显示HTML表格中的数据库结果。

For example, to show results from database in a HTML table during page load.

推荐答案

你可以使用 doGet（） servlet方法预处理请求并将请求转发给JSP。然后在链接和浏览器地址栏中指向servlet URL而不是JSP URL。

You can use the doGet() method of the servlet to preprocess a request and forward the request to the JSP. Then just point the servlet URL instead of JSP URL in links and browser address bar.

例如

@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);
    }

}

<%@ 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>

请注意，JSP文件放在 / WEB-INF 文件夹，防止用户直接访问它而不调用servlet。

Note that the JSP file is placed inside /WEB-INF folder to prevent users from accessing it directly without calling the servlet.

另请注意 @WebServlet 仅在Servlet 3.0（Tomcat 7等）之后才可用，另请参阅使用Tomcat 7的@WebServlet注释。如果您无法升级，或者由于某种原因需要使用与Servlet 3.0不兼容的 web.xml ，那么您需要手动注册如下所示，在 web.xml 中使用旧式方法而不是使用注释：

Also note that @WebServlet is only available since Servlet 3.0 (Tomcat 7, etc), see also @WebServlet annotation with Tomcat 7. If you can't upgrade, or when you for some reason need to use a web.xml which is not compatible with Servlet 3.0, then you'd need to manually register the servlet the old fashioned way in web.xml as below instead of using the annotation:

<servlet>
    <servlet-name>productsServlet</servlet-name>
    <servlet-class>com.example.ProductsServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>productsServlet</servlet-name>
    <url-pattern>/products</url-pattern>
</servlet-mapping>

一旦通过注释或XML正确注册了servlet，现在可以通过 http：// localhost：8080 / context / products 其中 / context 是webapp的已部署上下文路径， / products 是servlet的URL模式。如果你里面碰巧有任何HTML < form> ，那就让它POST到当前的网址，就像这样< form method =发布> 并添加 doPost（） 到同一个servlet来执行后处理工作。继续以下链接，了解更具体的例子。

Once having properly registered the servlet by annotation or XML, now you can open it by http://localhost:8080/context/products where /context is the webapp's deployed context path and /products is the servlet's URL pattern. If you happen to have any HTML <form> inside it, then just let it POST to the current URL like so <form method="post"> and add a doPost() to the very same servlet to perform the postprocessing job. Continue the below links for more concrete examples on that.

• 我们的Servlets维基页面


• 在Servlet中执行doGet和doPost


• 如何避免JSP中的Java代码


• 初级和中级JSP / Servlet教程

• Our Servlets wiki page
• doGet and doPost in Servlets
• How to avoid Java code in JSP
• Beginning and intermediate JSP/Servlet tutorials

这篇关于在页面加载时从JSP文件调用servlet的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！