如何从WebApp读取web.xml

要从WebApp读取web.xml文件，您需要使用Java的Servlet API。以下是一个简单的示例，展示了如何在Servlet中读取web.xml文件：

首先，确保您的web.xml文件位于应用程序的WEB-INF目录中。
在Servlet中，使用以下代码读取web.xml文件：

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

@WebServlet("/ReadWebXml")
public class ReadWebXmlServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        InputStream inputStream = getServletContext().getResourceAsStream("/WEB-INF/web.xml");
        Map<String, String> webXmlData = parseWebXml(inputStream);
        request.setAttribute("webXmlData", webXmlData);
        request.getRequestDispatcher("result.jsp").forward(request, response);
    }

    private Map<String, String> parseWebXml(InputStream inputStream) {
        Map<String, String> webXmlData = new HashMap<>();
        try {
            DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
            Document doc = dBuilder.parse(inputStream);
            doc.getDocumentElement().normalize();

            NodeList nList = doc.getElementsByTagName("servlet");
            for (int temp = 0; temp < nList.getLength(); temp++) {
                Node nNode = nList.item(temp);
                if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                    Element eElement = (Element) nNode;
                    String servletName = eElement.getElementsByTagName("servlet-name").item(0).getTextContent();
                    String servletClass = eElement.getElementsByTagName("servlet-class").item(0).getTextContent();
                    webXmlData.put(servletName, servletClass);
                }
            }
        } catch (ParserConfigurationException | SAXException | IOException e) {
            e.printStackTrace();
        }
        return webXmlData;
    }
}

在您的web.xml文件中，添加以下配置：

   <servlet-name>ReadWebXml</servlet-name>
   <servlet-class>com.example.ReadWebXmlServlet</servlet-class>
</servlet><servlet-mapping>
   <servlet-name>ReadWebXml</servlet-name>
    <url-pattern>/read-web-xml</url-pattern>
</servlet-mapping>

现在，当您访问http://your-domain.com/read-web-xml时，Servlet将读取web.xml文件并将数据传递给JSP页面。您可以在JSP页面中显示数据，例如：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8"><title>Web.xml Data</title>
</head>
<body>
    <h1>Web.xml Data</h1>
   <table>
        <tr>
            <th>Servlet Name</th>
            <th>Servlet Class</th>
        </tr>
        <% Map<String, String> webXmlData = (Map<String, String>) request.getAttribute("webXmlData"); %>
        <% for (String servletName : webXmlData.keySet()) { %>
        <tr>
            <td><%= servletName %></td>
            <td><%= webXmlData.get(servletName) %></td>
        </tr>
        <% } %>
    </table>
</body>
</html>

这样，您就可以从WebApp中读取web.xml文件并在JSP页面上显示数据。