@Size for length constraints in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a minimum length of 5 characters using @Size.

Spring Boot

@Size(min = [1])
private String username;

Drag options to blanks, or click blank then click option'

A3

B10

C0

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using max instead of min for minimum length.

Setting the value too low or zero when a minimum is needed.

The @Size annotation's min attribute sets the minimum length allowed. Here, 5 means the string must have at least 5 characters.

2fill in blank

medium

Complete the code to set a maximum length of 20 characters using @Size.

Spring Boot

@Size(max = [1])
private String password;

Drag options to blanks, or click blank then click option'

A10

B20

C30

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing min and max attributes.

Setting a maximum length smaller than the minimum length.

The max attribute in @Size sets the maximum allowed length. Here, 20 means the string cannot exceed 20 characters.

3fill in blank

hard

Fix the error in the @Size annotation to require a length between 3 and 15 characters.

Spring Boot

@Size(min = 3, max = [1])
private String nickname;

Drag options to blanks, or click blank then click option'

A15

B5

C10

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Setting max less than min causing validation errors.

Using incorrect numbers that don't match the requirement.

The max attribute should be 15 to set the upper limit of the allowed length range.

4fill in blank

hard

Fill both blanks to require a string length between 8 and 25 characters.

Spring Boot

@Size(min = [1], max = [2])
private String description;

Drag options to blanks, or click blank then click option'

A8

B10

C25

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping min and max values.

Choosing numbers outside the required range.

The min attribute is 8 and the max attribute is 25 to set the allowed length range.

5fill in blank

hard

Fill all three blanks to require a string length between 4 and 12 characters and add a custom error message.

Spring Boot

@Size(min = [1], max = [2], message = "[3]")
private String title;

Drag options to blanks, or click blank then click option'

A4

B12

CLength must be between 4 and 12 characters

DLength should be at least 5

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add the message attribute.

Using incorrect numbers for min or max.

Writing a message that does not match the length constraints.

The min is 4, max is 12, and the message provides a clear error message for validation failures.

Practice

1. What does the @Size annotation do in Spring Boot validation?

easy

A. It ensures a field is not null.

B. It validates if a number is within a range.

C. It checks if a string or collection length is within specified min and max limits.

D. It checks if a string matches a regular expression.

Solution

1. Step 1: Understand the purpose of @Size

   @Size is used to validate the length of strings or collections, not numeric ranges or null checks.

2. Step 2: Identify what @Size checks

   It uses min and max to set length limits on text or collections.

3. Final Answer:

   It checks if a string or collection length is within specified min and max limits. -> Option C

4. Quick Check:

   @Size validates length = C [OK]

Hint: Remember @Size controls length, not value or null checks [OK]

Common Mistakes:

• Confusing @Size with @Min/@Max for numbers
• Thinking @Size checks null values
• Assuming @Size validates patterns

2. Which of the following is the correct way to use @Size to require a string between 5 and 10 characters?

easy

A. @Size(min=5, max=10)

B. @Size(length=5-10)

C. @Size(minLength=5, maxLength=10)

D. @Size(range={5,10})

Solution

1. Step 1: Recall correct @Size syntax

   The correct attributes are min and max for length limits.

2. Step 2: Check each option

   Only @Size(min=5, max=10) uses valid attribute names and syntax.

3. Final Answer:

   @Size(min=5, max=10) -> Option A

4. Quick Check:

   Use min and max attributes = A [OK]

Hint: Use min and max, not length or range attributes [OK]

Common Mistakes:

• Using invalid attribute names like length or range
• Trying to pass a range as a string
• Confusing @Size with other annotations

3. Given this code snippet:

@Size(min=3, max=6)
private String code;

Which input value will pass validation?

medium

A. "ab"

B. "abcde"

C. "abcdefg"

D. ""

Solution

1. Step 1: Understand the length limits

   The string must have length between 3 and 6 characters inclusive.

2. Step 2: Check each input length

   "ab" length is 2 (too short), "abcdefg" length is 7 (too long), "abcde" length is 5 (valid), "" length is 0 (too short).

3. Final Answer:

   "abcde" -> Option B

4. Quick Check:

   Length between 3 and 6 = "abcde" [OK]

Hint: Count characters; must be between min and max [OK]

Common Mistakes:

• Ignoring inclusive limits
• Counting characters incorrectly
• Assuming empty string passes

4. Identify the error in this code snippet:

@Size(min=2, max=5)
private int number;

medium

A. @Size cannot be applied to primitive types like int.

B. min and max values are reversed.

C. Missing @NotNull annotation.

D. max value should be greater than 10.

Solution

1. Step 1: Check @Size target types

   @Size works on strings, collections, arrays, but not on primitive types like int.

2. Step 2: Analyze the code

   The field is an int, so @Size is invalid here and will cause an error.

3. Final Answer:

   @Size cannot be applied to primitive types like int. -> Option A

4. Quick Check:

   @Size only for strings/collections = D [OK]

Hint: Use @Size only on strings or collections, not primitives [OK]

Common Mistakes:

• Applying @Size to numbers
• Confusing @Size with @Min/@Max for numbers
• Ignoring type compatibility

5. You want to validate a list of usernames where each username must be between 4 and 12 characters. Which is the correct way to apply @Size in your Spring Boot model?

hard

A. @Size(min=4, max=12) private List<@Size(min=4, max=12)> usernames;

B. @Size(min=4, max=12) private String[] usernames;

C. @Size(min=4, max=12) private List<String> usernames;

D. private List<@Size(min=4, max=12) String> usernames;

Solution

1. Step 1: Understand @Size on collections vs elements

   @Size on a collection checks the collection size, not each element's length.

2. Step 2: Apply @Size to elements inside the collection

   To validate each username's length, use @Size on the generic type parameter or element level.

3. Step 3: Analyze options

   private List<@Size(min=4, max=12) String> usernames; correctly applies @Size to each String element in the List.

4. Final Answer:

   private List<@Size(min=4, max=12) String> usernames; -> Option D

5. Quick Check:

   Use @Size on elements for per-item length = D [OK]

Hint: Put @Size on list elements, not just the list itself [OK]

Common Mistakes:

• Applying @Size only on the list, not elements
• Using invalid syntax for generic annotations
• Confusing collection size with element length