TCPMon is a good TCP/IP tool to intercept the traffic that is being passed and shows the payload of the traffic. Sometimes when you are passing a cookie, or some other meta data you want to be sure if everything is being passed correctly. The tool also allows to simulate a slow connection. Which is ideal to reproduce timeout and/or performance issues.
TCPMon is not supported anymore but it is still one of the most populair tools out here. If you have a better alternative, feel free to mention them.
You can install TCPMon in IntelliJ as a plugin and it will appear in your toolbar.
Now when you make requests to port 8081, it will redirect to 127.0.0.1:8080. You will see the following output