Request DTO for input in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a simple Request DTO class with a private field and its getter.

Spring Boot

public class UserRequestDTO {
    private String [1];

    public String getUsername() {
        return username;
    }
}

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

Aname

Busername

CuserName

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using a field name that does not match the getter method name.

Using uppercase letters at the start of the field name.

The field name must match the getter method name. Here, the getter is getUsername(), so the field should be username.

2fill in blank

medium

Complete the code to add a setter method for the field in the Request DTO.

Spring Boot

public void [1](String username) {
    this.username = username;
}

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

AupdateUsername

BsetUser

CgetUsername

DsetUsername

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' instead of 'set' in the method name.

Using a method name that does not match the field name.

Setter methods in Java follow the pattern setFieldName. Here, the field is username, so the setter is setUsername.

3fill in blank

hard

Fix the error in the annotation to make this class a valid Request DTO in Spring Boot.

Spring Boot

@[1]
public class UserRequestDTO {
    private String username;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

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

AData

BEntity

CRequestBody

DRestController

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Entity which is for database entities.

Using @RestController which is for controllers.

Using @RequestBody which is for method parameters.

The @Data annotation from Lombok generates getters and setters automatically, making the DTO concise and valid.

4fill in blank

hard

Fill both blanks to create a Request DTO with validation annotations for a non-empty username.

Spring Boot

import jakarta.validation.constraints.[1];

public class UserRequestDTO {
    @[2](message = "Username cannot be empty")
    private String username;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

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

ANotBlank

BNotNull

CSize

DEmail

Attempts:

3 left

💡 Hint

Common Mistakes

Using @NotNull which allows empty strings.

Using @Email which is for email format validation.

The @NotBlank annotation ensures the username is not null and not empty after trimming spaces.

5fill in blank

hard

Fill all three blanks to create a Request DTO with username and age fields, including validation for non-empty username and minimum age 18.

Spring Boot

import jakarta.validation.constraints.[1];
import jakarta.validation.constraints.[2];

public class UserRequestDTO {
    @[3](message = "Username cannot be empty")
    private String username;

    @Min(18)
    private int age;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

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

ANotBlank

BMin

CNotNull

DSize

Attempts:

3 left

💡 Hint

Common Mistakes

Importing @NotNull instead of @NotBlank for username.

Not importing @Min for age validation.

Import NotBlank for username validation and Min for age validation. The username field uses @NotBlank.

Practice

1. What is the main purpose of a Request DTO in a Spring Boot application?

easy

A. To configure the application server settings

B. To store data directly in the database

C. To handle HTTP responses sent to the client

D. To organize and validate user input separately from database models

Solution

1. Step 1: Understand what a Request DTO is

   A Request DTO (Data Transfer Object) is used to receive and organize input data from users in a clean way.

2. Step 2: Differentiate from other components

   Unlike database models, Request DTOs focus only on input validation and structure, not on storing data.

3. Final Answer:

   To organize and validate user input separately from database models -> Option D

4. Quick Check:

   Request DTO = Input organization and validation [OK]

Hint: Request DTOs separate input from database models [OK]

Common Mistakes:

• Confusing DTO with database entity
• Thinking DTO handles HTTP responses
• Assuming DTO configures server

2. Which of the following is the correct way to declare a simple Request DTO class in Spring Boot to receive a user's name and age?

easy

A. public interface UserRequest { String getName(); int getAge(); }

B. public class UserRequest { private String name; private int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }

C. @Entity public class UserRequest { private String name; private int age; }

D. @Controller public class UserRequest { private String name; private int age; }

Solution

1. Step 1: Identify the correct DTO structure

   A Request DTO is a simple Java class with private fields and public getters/setters to hold input data.

2. Step 2: Check annotations and class type

   It should NOT be an entity or controller; those are for database and web layers respectively.

3. Final Answer:

   Plain Java class with private fields and getters/setters -> Option B

4. Quick Check:

   DTO = Plain class with getters/setters [OK]

Hint: DTOs are plain classes, not entities or controllers [OK]

Common Mistakes:

• Using @Entity annotation on DTO
• Making DTO an interface
• Annotating DTO as @Controller

3. Given the following Request DTO and controller method, what will be the output if the JSON input is {"name":"Alice","age":30}?

public class UserRequest {
  private String name;
  private int age;
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }
  public int getAge() { return age; }
  public void setAge(int age) { this.age = age; }
}

@PostMapping("/user")
public String createUser(@RequestBody UserRequest request) {
  return "User: " + request.getName() + ", Age: " + request.getAge();
}

medium

A. User: null, Age: 0

B. Compilation error due to missing annotations

C. User: Alice, Age: 30

D. Runtime error due to invalid JSON

Solution

1. Step 1: Understand JSON to DTO mapping

   The JSON keys match the DTO fields, so Spring Boot maps "name" to name and "age" to age correctly.

2. Step 2: Check controller return value

   The method returns a string combining name and age from the DTO, so it outputs "User: Alice, Age: 30".

3. Final Answer:

   User: Alice, Age: 30 -> Option C

4. Quick Check:

   Matching JSON fields produce correct output [OK]

Hint: Matching JSON keys to DTO fields maps input correctly [OK]

Common Mistakes:

• Assuming missing annotations cause errors
• Expecting null values despite matching JSON
• Confusing runtime errors with mapping

4. Identify the error in this Request DTO class that causes Spring Boot to fail binding JSON input:

public class ProductRequest {
  private String productName;
  private int quantity;
  public int getQuantity() { return quantity; }
  public void setQuantity(int quantity) { this.quantity = quantity; }
}

medium

A. Missing getter and setter for productName field

B. Quantity field should be public

C. Class must be annotated with @RequestBody

D. No default constructor defined

Solution

1. Step 1: Check field access and methods

   productName lacks getter/setter, so Spring cannot bind JSON to it properly.

2. Step 2: Validate other options

   Quantity has proper getter/setter; @RequestBody is for method parameters, not classes; default constructor is implicit.

3. Final Answer:

   Missing getter and setter for productName field -> Option A

4. Quick Check:

   DTO fields need getters/setters for binding [OK]

Hint: DTO fields need getters/setters for JSON binding [OK]

Common Mistakes:

• Thinking public fields bind without getters/setters
• Adding @RequestBody on DTO class
• Assuming default constructor must be explicit

5. You want to ensure that the email field in your Request DTO is not empty and follows a valid email format. Which annotations should you add to the email field to achieve this validation automatically in Spring Boot?

hard

A. @NotEmpty and @Email

B. @Valid and @NotNull

C. @Size(min=1) and @Pattern(regexp=".+@.+\\..+")

D. @NotBlank and @JsonProperty

Solution

1. Step 1: Identify validation annotations for non-empty and email format

   @NotEmpty ensures the field is not empty, and @Email checks for valid email format.

2. Step 2: Evaluate other options

   @Valid is for nested validation, @NotNull allows empty strings, @Size and @Pattern can work but are more complex; @JsonProperty is for JSON mapping, not validation.

3. Final Answer:

   @NotEmpty and @Email -> Option A

4. Quick Check:

   Use @NotEmpty and @Email for email validation [OK]

Hint: Use @NotEmpty and @Email for email validation [OK]

Common Mistakes:

• Using @NotNull which allows empty strings
• Confusing @Valid with validation annotations
• Using @JsonProperty for validation