Detailed explanation of the solution to Tomcat's 404 error

The 404 problem occurs in the Tomcat test. The problems are as follows:

HTTP Status 404 - Not Found Type Status Report Message The requested resource [/chapter06/IndexServlet] is not available Description The origin server was unable to find a representation for the target resource or is unwilling to expose an existing representation for the resource.
Apache Tomcat/9.0.37

The problem is that the browser cannot directly access the Java file.

Solution to the problem

1. This problem occurs when submitting a form

<form name = "reg" action="/login" method="post">
 <meta charset="UTF-8">
 Account: <input type="text" name="username"/><br>
 Password: <input type="password" name="passward"/><br>
 <input type="submit" value="Submit" id="bt">
</form>

The reference in <form name = "reg" action="/login" method="post"> action=" " must be a routing address (this routing address needs to be configured by yourself (for example, the route in the Java class responsible for receiving the form I configured myself is /login, not the access path of my own Java class /chapter06/src/LoginServlet)
The way to configure routing for Java files is as follows:

2. Accessing the Java file in the src path reports an error

You need to configure routing for the target Java file. There are two ways to configure it: (This is just a brief description. If you want to know more details, click here)

(1): Configuration based on annotations

Only applicable to Tomcat 3 and above (I think it is 3, I can't remember)
Add in the Java class

package cn.itcast.chapter06.session.example;

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 java.io.IOException;
@WebServlet("/logout") //Here is the routing configuration public class LogoutServlet extends HttpServlet {
 @Override
 public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  req.getSession().removeAttribute("user");
  resp.sendRedirect("/wel");
 }

 @Override
 public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  doGet(req, resp);
 }
}

**@WebServlet("/logout") //Here is the routing configuration, which is also the most commonly used method. **The quotation marks are for routing

(2) Configuration based on XML file

Click to open the web.xml file, then modify the web.xml code and add a mapping before < /app >

<servlet> 
	 <servlet-name>hello</servlet-name> 
	 <servlet-class>com.southwind.servlet.HelloServlet</servlet-class>
 </servlet>
<servlet-mapping> 
	<servlet-name>hello</servlet-name> 
	<url-pattern>/demo2</url-pattern> 
</servlet-mapping>

Map demo2 and hello. You can map HelloServlet by directly accessing demo2 in the browser.

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