Why I got HTTP 404 error when I run my dynamic web project?

Question

When I run my project it shows 404 error. To run successful I have to type my class name in the URL. My Servlet class First.java

import java.io.*;
import javax.servlet.*;
@WebServlet("/First")
public class First implements Servlet {

    public void init(ServletConfig req) throws ServletException {
        System.out.println("Initial");
        
    }

    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        System.out.println("Service");
        
    }
     
    public void destroy()
    {
    }
}

My XML file web.xml

<?xml version="1.0" encoding="UTF-8"?>
<element>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>FirstProject</display-name>
  <servlet>
    <servlet-name>firstServlet</servlet-name>
    <servlet-class>First</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>firstServlet</servlet-name>
    <url-pattern>/First</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
</web-app>
</element>

Like http://localhost:8085/FirstProject/ shows 404 error but http://localhost:8085/FirstProject/First provide the desired output. When I click submit button in my login project it must provides desired output page but it didn't show. I have to type the servlet URL mapping name. Why this is happens please help me!

Answer 1

http://localhost:8085/FirstProject/First is the correct URL. The format will be like the following:

http://<IP_ADDRESS>:<PORT>/<CONTEXT_NAME>/<ADAPTER_NAME>

ADAPTER_NAME is the name we give as the url-pattern in the servlet mapping. CONTEXT_NAME is the ProjectName or the WAR name usually.