While there are many techniques which are language agnostic, these are some of my favorites with Spring Boot.

Project Lombok

Use this if you don’t use Spring Boot with Kotlin. This will module will reduce side of code by around 15-25%.

Lombok allows you to generate java boilerplate at runtime by using Annotations such as: @ToString, @EqualsAndHashCode, @Getter/@Setter, etc.

My favorite onces are

• @Data: A shortcut for @ToString, @EqualsAndHashCode, @Getter on all fields, and @Setter on all non-final fields, and @RequiredArgsConstructor.
• @Cleanup: Automatically calls close() method in case of Streams and Connections.

@RequestParam without Arguments

If the name of variable is same as value in @RequestParam, remove @Request Param.

Remove @Column on @Entity

In a @Entity, if the name of variable is same name of column writing @Column is unnecessary.

By doing this, not only remove a line from every variable, the quality of code is better as there is naming is consistent between DB and backend.

Use JPA @Repository Methods instead of Hibernate EntityManager/JdbcTemplate

Ideally your queries should be so simple such that the only type of read operation you do is simple CRUD.

Such simple queries are easier to understand and are a good sign of a well designed database.

Such operations are available out of the box with @Repository.