Demo: 1. Create Java Web Application

July 2025

Create a Java web application using JSP and Servlet, deploy it on Apache Tomcat, and display dynamic links generated by backend logic.

1. 📁 Project Structure Setup

Create a basic Maven or dynamic web project with the following structure:

MyWebApp/
├── src/
│   └── main/
│       └── java/
│           └── com/
│               └── example/
│                   ├── DemoServlet.java
│                   ├── DemoApp.java
│                   └── Demo2App.java
├── web/
│   └── index.jsp
├── WEB-INF/
│   ├── web.xml
├── pom.xml

2. 🧠 Backend Logic

Ensure you have the following classes:

DemoServlet.java

package com.example;

import jakarta.servlet.*;
import jakarta.servlet.http.*;
import java.io.IOException;

public class DemoServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        resp.setContentType("text/html");
        String para = req.getParameter("p");
        if ("2".equals(para)){
            resp.getWriter().write("<h1>" + Demo2App.getMessage() + "</h1>");
        }else{
            resp.getWriter().write("<h1>" + DemoApp.getMessage() + "</h1>");
        }
        
        
    }
}

DemoApp.java and Demo2App.java with static getMessage() methods:

package com.example;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

public class DemoApp {
    public static String getMessage() {
        try {
            Document doc = Jsoup.connect("https://www.hku.hk").get();
            String title = doc.title();
            return "Website Title: " + title;
        } catch (Exception e) {
            return "Failed to fetch title: " + e.getMessage();
        }
    }
}

package com.example;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

public class Demo2App {
    static String urlname="https://www.hku.edu.hk";

    public static String getMessage() {
        try {
            Document doc = Jsoup.connect(urlname).get();
            String title = doc.title();
            return "Website Title: " + title;
        } catch (Exception e) {
            return "Failed to fetch title: " + e.getMessage();
        }
    }
}

3. 📝 JSP Page (index.jsp)

Create a JSP file that links to the servlet with different parameters:

<!DOCTYPE html>
<html>
<head><title>Welcome</title></head>
<body>
    <h2>Welcome to the WAR App</h2>
    <p><a href="demo">Click here to see the message</a></p>
     <p><a href="demo?p=2">Can you fix it to display the same message above</a></p>
</body>
</html>

4. 🧾 web.xml Configuration

Define the servlet and mapping in WEB-INF/web.xml:

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >


<web-app xmlns="http://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://jakarta.ee/xml/ns/jakartaee
                             http://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">

    <servlet>
        <servlet-name>DemoServlet</servlet-name>
        <servlet-class>com.example.DemoServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>DemoServlet</servlet-name>
        <url-pattern>/demo</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>