I want to get the data from DB and send the data by Http communication while considering the order.

If you would like to do the following, please let me know if you have any good middleware (library) or methods.

There is an API server that accepts requests from clients and
This server writes records to DB in consideration of the order of transmission.

For example, suppose that the data types are numbered A, B, and C in order from 1
Assume that those with different data types can be transmitted simultaneously, and the serial number must be transmitted in order within the same data type.
(Example A-1 and B-2 can be sent at the same time; A-2 can be sent after A-1 has been sent)
Also, we expect to resend it when it is not sent.

If you want to do this, I think it's better to build a system separately from accepting online requests.
(Resident and notify the DB to be written or new system for processing.Resend at any time)

Current API Server Environment
(I don't know the version, but it was built around 2013)

OS:RHEL
Application: Java Servlet (running on Tomcat)
DB:postgresql

We would like to build Java from the current system configuration as much as possible, but we will consider any other useful ones.Freeware only.

I would appreciate it if you could reply.