There are two reasons for the problem
Your idea is a good tomcat server is not configured
Specific configuration: https://jingyan.baidu.com/article/dca1fa6f0c34bcf1a4405232.html (How to configure Tomcat server Intellij IDEA)
A second possible reason for this is the wrong application deployment environment
General idea will let you specify a folder for the application environment, then they would deploy the application environment again when you write a new entry
How good a one-time deployment
After entering the screen, click on Deployment, then click the plus sign rightmost, adding ROOT under the webapps tomcat you install
Then the following Application context with a direct / line
Deployment in the Edit Configurations
