It is a SpringBoot application which has 3 GET and 1 POST REST API.
It has h2 database for data persistence.
When building applications, I usually go with this architecture.

I like using the DTO pattern to seperate the communication between the layers.
It also helps with testability of the code.

The application should be working without any additional setup.

DATABASE
Endpoint to connect to h2 database is http://localhost:8080/h2-console
Database user name is "sa" and password is not needed.

Your H2 databse setup should look this to be able to connect to embedded database.

I have inserted some data to be able to test the application.
If you feel you need to add more data, feel free to edit this file:
https://github.com/MarinPuizina/MeterReadings/blob/master/src/main/resources/data-h2.sql

Potential issues
The only potential issues that I can think of, is with the H2 dependency.
In the pom.xml file:
https://github.com/MarinPuizina/MeterReadings/blob/master/pom.xml

I am using specific version for H2.

You can try removing the version and let Spring decide which one it is going to use.

GET

1. http://localhost:8080/readings/addresses/Ulica 7/years/2019
2. http://localhost:8080/readings/addresses/Ulica 7/years/2019/months
3. http://localhost:8080/readings/addresses/Marmontova/years/2019/months/September

POST

1. http://localhost:8080/readings
   body:
   { "client": "Marin Puizina", "address": "Ulica 7", "year": 2019, "month": "November", "reading": 7 }