@NotNull, @NotBlank, @NotEmpty in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @NotNull annotation check in Spring Boot validation?

It checks that the annotated field is not null. However, it does not check if the field is empty if it is a String or collection.

beginner

How is @NotBlank different from @NotNull?

@NotBlank checks that a String is not null and also not empty or only whitespace. It is stricter than @NotNull for Strings.

beginner

What type of fields is @NotEmpty used for?

@NotEmpty is used for Strings, Collections, Maps, or arrays to ensure they are not null and not empty (length > 0).

intermediate

Which annotation would you use to ensure a list is not null and has at least one element?

You would use @NotEmpty because it checks both for null and that the collection has at least one element.

intermediate

Can @NotBlank be applied to a List or Collection?

No, @NotBlank is only for CharSequence (like String). For collections, use @NotEmpty to check for non-null and non-empty.

Which annotation ensures a String is not null, not empty, and not just whitespace?

A @NotEmpty

B @NotNull

C @NotBlank

D @Valid

@NotBlank checks for null, empty, and whitespace-only Strings.

Which annotation can be used on a List to ensure it is not null and has elements?

A @NotBlank

B @NotNull

C @Size(min=1)

D @NotEmpty

@NotEmpty ensures the collection is not null and not empty.

What does @NotNull validate?

A Field is not null

B Field is not empty

C Field is not blank

D Field has minimum size

@NotNull only checks that the value is not null.

Which annotation would fail validation for a String with only spaces?

A @NotNull

B @NotBlank

C None of these

D @NotEmpty

@NotBlank fails if the String is only whitespace.

If you want to allow empty strings but not null, which annotation should you use?

A @NotNull

B @NotEmpty

C No annotation needed

D @NotBlank

@NotNull allows empty strings but disallows null values.

Explain the differences between @NotNull, @NotBlank, and @NotEmpty annotations in Spring Boot validation.

Think about what each annotation checks for and on which data types.

Describe a real-life example where you would use @NotBlank instead of @NotNull.

Consider a form field where blank spaces should not be accepted.