Servlet class is not working in my file upload program

Question

I have done everything well, but my servlet class is not found, When I run the file it runs but when I click upload It shows error,

package com.example.ServletBlog;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import java.io.*;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import javax.servlet.annotation.*;

public class HelloServlet extends HttpServlet {
    private final String UPLOAD_DIRECTORY = "src/main/resources";

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        //process only if its multipart content
        if(ServletFileUpload.isMultipartContent(request)){
            try {
                List<FileItem> multiparts = new ServletFileUpload(
                        new DiskFileItemFactory()).parseRequest(request);

                for(FileItem item : multiparts){
                    if(!item.isFormField()){
                        String name = new File(item.getName()).getName();
                        item.write( new File(UPLOAD_DIRECTORY + File.separator + name));
                    }
                }

                //File uploaded successfully
                request.setAttribute("message", "File Uploaded Successfully");
            } catch (Exception ex) {
                request.setAttribute("message", "File Upload Failed due to " + ex);
            }

        }else{
            request.setAttribute("message",
                    "Sorry this Servlet only handles file upload request");
        }

        request.getRequestDispatcher("/result.jsp").forward(request, response);

    }


}

The program is to upload a file

<servlet>
    <servlet-name>HelloServlet</servlet-name>
    <servlet-class>com.example.ServletBlog.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>HelloServlet</servlet-name>
    <url-pattern>/upload</url-pattern>
</servlet-mapping>


<session-config>
    <session-timeout>
        30
    </session-timeout>
</session-config>

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

When I run the file it runs but when I click upload It shows error,

result.jsp

<div id="result">
    <h3>${requestScope["message"]}</h3>
</div>

When I run the file it runs but when I click upload It shows error,

index.jsp

<form action="upload" method="post" enctype="multipart/form-data">
    <input type="file" name="file" />
    <input type="submit" value="upload" />
</form>

When I run the file it runs but when I click upload It shows error,