Exceptions and records

Java has two kinds of exceptions. Checked exceptions must be caught or declared, and the compiler forces you to do it. Unchecked ones, such as IllegalArgumentException, signal bugs or bad input.

Learn try, catch and finally. Learn try-with-resources too, which closes connections and streams for you automatically. Create your own exceptions for business errors, such as OrderNotFoundException.

Spring will later turn that into a 404 in one place. Records are the other half of this topic. One line, record Order(long id, BigDecimal total) {}, gives you an unchangeable data class.

It comes with a constructor, accessors, equals, hashCode and toString already written. That makes records ideal for request and response bodies.