Boolean Field Becomes null in Spring Boot DTO? Here’s Why (And How to Fix It)

If you’re building REST APIs using Spring Boot, you may encounter a strange and frustrating issue:
❓ The request JSON clearly sends a boolean value (true / false),
but inside the DTO, the value becomes null.

• No exception.
• No warning.
• No stack trace.

This is not a bug in Spring Boot — it’s a Jackson + Java Bean naming trap that frequently appears in real-world applications.

In this article, you’ll learn:

1. - Why boolean values become null in Spring Boot DTOs
2. - How Jackson maps JSON properties to Java fields
3. - Why @JsonProperty fixes the issue
4. - The recommended best practice to avoid this forever

The Problem: Boolean Value Is null in DTO

Consider this request payload sent from the frontend:

{
  "isActive": true
}

Now look at the DTO:

public class UserRequest {

    private Boolean isActive;

    public Boolean getIsActive() {
        return isActive;
    }

    public void setIsActive(Boolean isActive) {
        this.isActive = isActive;
    }
}

Controller code:

@PostMapping("/user")
public void createUser(@RequestBody UserRequest request) {
    System.out.println(request.getIsActive());
}

Actual Output

null

❌ JSON is correct
❌ Mapping fails silently
❌ Debugging becomes painful

Why This Happens (Jackson + Java Bean Rules)
Spring Boot uses Jackson to convert JSON into Java objects.

Jackson does not rely only on field names — it follows Java Bean naming conventions, which depend heavily on getter and setter names.

How Jackson Interprets Boolean Fields
For this field:

private Boolean isActive;

Jackson expects one of these method patterns:

public Boolean isActive()

or

public Boolean getActive()

But what we actually wrote:

public Boolean getIsActive()

The Mismatch

JSON property: isActive
Java property Jackson infers: active
Because of this mismatch, Jackson fails to bind the value — resulting in null.

Solution 1: Use @JsonProperty (Quick Fix)

You can explicitly tell Jackson how to map the JSON property.

Fixed DTO Using @JsonProperty

import com.fasterxml.jackson.annotation.JsonProperty;

public class UserRequest {

    @JsonProperty("isActive")
    private Boolean isActive;

    public Boolean getIsActive() {
        return isActive;
    }

    public void setIsActive(Boolean isActive) {
        this.isActive = isActive;
    }
}

Result

✔ JSON maps correctly
✔ DTO receives true / false
✔ No more null

Solution 2: Best Practice (Highly Recommended)

Instead of fixing the mapping, fix the design.

Avoid starting boolean field names with is.
Preferred DTO Design

public class UserRequest {

    private Boolean active;

    public Boolean getActive() {
        return active;
    }

    public void setActive(Boolean active) {
        this.active = active;
    }
}

Why This Is Better

Fully Java Bean compliant

• No Jackson annotations required
• Cleaner, more readable DTOs
• Fewer bugs in large codebases

boolean vs Boolean in Spring Boot DTOs

Type	Default Value	Nullable
boolean	false	No
Boolean	null	Yes

When to Use What

• Use boolean when the field is mandatory
• Use Boolean when the field is optional or tri-state

Common Interview Question

Q: Why does Spring Boot map boolean JSON values to null?
Answer:
Because Jackson follows Java Bean naming conventions. Boolean fields prefixed with is can cause property name mismatches unless getters, setters, or @JsonProperty are defined correctly.

Key Takeaways

• Boolean fields starting with is can silently break Jackson mapping
• Jackson relies on getter/setter naming, not field names
• @JsonProperty fixes the issue explicitly
• Best practice: avoid is prefix in DTO fields
• Always check DTO design before debugging controllers

Final Advice

If your JSON looks correct but your DTO value is null:
👉 Check the getter and setter naming first.
This small detail can save hours of debugging in Spring Boot applications.