How load servlet on index.jsp

Just change the welcome file URL to be the one of the servlet.

Given this servlet mapping,

<servlet-mapping>
    <servlet-name>indexServlet</servlet-name>
    <url-pattern>/index</url-pattern>
</servlet-mapping>

just have this welcome file list:

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

Don't forget to move the /index.jsp into /WEB-INF folder to prevent it from being accessed directly by endusers guessing its URL (and don't forget to alter the forward call in the index servlet to point to /WEB-INF/index.jsp).

Or if you solely intend to have a "home page servlet" and not an "index servlet", then map the servlet to the empty string URL pattern instead of as welcome file.

<servlet-mapping>
    <servlet-name>indexServlet</servlet-name>
    <url-pattern></url-pattern>
</servlet-mapping>

See also:

• How to call a servlet on jsp page load?
• Difference between / and /* in servlet mapping url pattern