@NotNull, @NotBlank, @NotEmpty in Spring Boot - Performance & Optimization

Performance: @NotNull, @NotBlank, @NotEmpty

LOW IMPACT

These annotations affect server-side validation speed and response time but have minimal impact on frontend rendering or page load.

Validating user input fields in a Spring Boot application

Spring Boot

@NotBlank
private String name;

@NotBlank
private String email;

@NotEmpty
private List<String> tags;

Using the most appropriate annotation per field reduces redundant checks and speeds up validation.

📈 Performance GainReduces validation CPU overhead, improving server response time by a small margin.

Validating user input fields in a Spring Boot application

Spring Boot

@NotNull
private String name;

@NotBlank
private String email;

@NotEmpty
private List<String> tags;

Using all three annotations redundantly on the same field or on fields where simpler validation suffices can add unnecessary validation checks.

📉 Performance CostAdds extra CPU cycles during request processing, slightly increasing server response time.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Using @NotNull, @NotBlank, @NotEmpty appropriately on server-side	0	0	0	[OK] Good
Redundant or unnecessary validation annotations on same fields	0	0	0	[!] OK
Client-side validation only without server validation	0	0	0	[X] Bad (security risk)

Rendering Pipeline

These annotations run on the server during request validation and do not affect the browser rendering pipeline directly.

⚠️ BottleneckNone in browser rendering; possible minor CPU usage on server during validation.

Optimization Tips

1Use @NotNull for fields that must not be null but can be empty strings or collections.

2Use @NotBlank for Strings that must contain non-whitespace characters.

3Use @NotEmpty for collections or strings that must not be null and must not be empty.

Performance Quiz - 3 Questions

Which annotation should you use to ensure a String is not null and not empty after trimming whitespace?

A @NotEmpty

B @NotNull

C @NotBlank

D None of these

DevTools: Network

How to check: Use the Network panel to measure server response times for requests with and without validation annotations.

What to look for: Look for increased server response time indicating heavier validation processing.

Practice

1. Which annotation ensures a string field in a Spring Boot application is not null, but allows empty strings?

easy

A. @NotEmpty

B. @NotBlank

C. @NotNull

D. @Valid

Solution

1. Step 1: Understand @NotNull behavior

   @NotNull only prevents the value from being null but allows empty strings or collections.

2. Step 2: Compare with other annotations

   @NotEmpty and @NotBlank prevent empty values, so they are stricter than @NotNull.

3. Final Answer:

   @NotNull -> Option C

4. Quick Check:

   @NotNull allows empty but not null [OK]

Hint: Remember: @NotNull forbids null, allows empty [OK]

Common Mistakes:

• Confusing @NotNull with @NotEmpty or @NotBlank
• Thinking @NotNull forbids empty strings
• Assuming @Valid checks null automatically

2. Which of the following is the correct way to annotate a string field that must not be null, empty, or only spaces in Spring Boot?

easy

A. @NotBlank private String name;

B. @NotEmpty private String name;

C. @NotNull @NotEmpty private String name;

D. @NotNull private String name;

Solution

1. Step 1: Identify annotation that forbids null, empty, and spaces

   @NotBlank ensures the string is not null, not empty, and not just whitespace.

2. Step 2: Check other options

   @NotNull allows empty or spaces; @NotEmpty forbids empty but allows spaces; only @NotBlank covers all three.

3. Final Answer:

   @NotBlank private String name; -> Option A

4. Quick Check:

   @NotBlank forbids null, empty, spaces [OK]

Hint: Use @NotBlank for strings with no spaces or empties [OK]

Common Mistakes:

• Using @NotEmpty but ignoring spaces
• Combining @NotNull and @NotEmpty unnecessarily
• Assuming @NotNull forbids empty strings

3. Given the code snippet:

@NotEmpty
private List<String> tags;

What happens if tags is set to an empty list during validation?

medium

A. Validation passes because list is not null

B. Validation fails because list is empty

C. Validation fails only if list is null

D. Validation passes regardless of list content

Solution

1. Step 1: Understand @NotEmpty on collections

   @NotEmpty forbids null or empty collections, so empty list fails validation.

2. Step 2: Compare with other annotations

   @NotNull allows empty list; @NotEmpty forbids empty; @NotBlank is for strings only.

3. Final Answer:

   Validation fails because list is empty -> Option B

4. Quick Check:

   @NotEmpty forbids empty collections [OK]

Hint: @NotEmpty forbids empty lists or strings [OK]

Common Mistakes:

• Thinking empty list passes @NotEmpty
• Confusing @NotEmpty with @NotNull
• Applying @NotBlank to collections

4. Consider this code snippet:

@NotBlank
private String title;

Which of the following values for title will cause validation to fail with @NotBlank but pass with @NotEmpty?

medium

A. " " (string with spaces only)

B. "Hello"

C. "" (empty string)

D. null

Solution

1. Step 1: Understand @NotBlank validation rules

   @NotBlank forbids null, empty, and strings with only whitespace.

2. Step 2: Analyze each value

   null and "" fail both @NotBlank and @NotEmpty; "Hello" passes both; " " passes @NotEmpty (length > 0) but fails @NotBlank (trimmed length = 0).

3. Final Answer:

   " " (string with spaces only) -> Option A

4. Quick Check:

   @NotBlank forbids spaces-only strings [OK]

Hint: @NotBlank forbids spaces-only strings [OK]

Common Mistakes:

• Assuming empty string passes @NotBlank
• Confusing @NotBlank with @NotEmpty
• Ignoring spaces-only strings as invalid

5. You want to validate a user input field description that must not be null, empty, or only spaces, but also must allow strings like "0" or "false". Which annotation should you use in Spring Boot?

hard

A. @Size(min=1)

B. @NotEmpty

C. @NotNull

D. @NotBlank

Solution

1. Step 1: Understand requirements for description

   Must not be null, empty, or spaces-only, but allow "0" or "false" strings.

2. Step 2: Match annotation behavior

   @NotBlank forbids null, empty, and spaces-only strings but allows "0" and "false" as they are non-blank strings.

3. Step 3: Check alternatives

   @NotNull allows empty; @NotEmpty forbids empty but allows spaces; @Size(min=1) forbids empty but not spaces-only.

4. Final Answer:

   @NotBlank -> Option D

5. Quick Check:

   @NotBlank fits all conditions [OK]

Hint: Use @NotBlank to forbid null, empty, and spaces-only [OK]

Common Mistakes:

• Using @NotEmpty and missing spaces-only strings
• Assuming @Size(min=1) forbids spaces-only
• Confusing @NotNull with stricter annotations