Spring Boot Returning HTML Instead of JSON: How to Fix with @ResponseBody

Apr 23, 2026

Problem

When I called my Spring Boot REST endpoint, the frontend got an error:

SyntaxError: Unexpected token < in JSON at position 0

My endpoint returned a List<User> but the frontend received an HTML page instead of JSON data.

Environment

Spring Boot backend
Angular frontend
REST endpoint supposed to return JSON

What Happened?

I had a controller like this:

@Controller
public class UserController {

    @GetMapping("/users")
    public List&lt;User&gt; getUsers() {
        return userRepository.findAll();
    }
}

I expected JSON output like:

[
  {"id": 1, "name": "John", "lastname": "Doe"},
  {"id": 2, "name": "Jane", "lastname": "Smith"}
]

But the actual response was:

&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
  &lt;title&gt;Error&lt;/title&gt;
...

Why did Spring return HTML instead of JSON?

The Reason

The @Controller annotation tells Spring MVC that this class returns view names. Spring tries to find a template named “List<User>” or similar, and when it fails, it falls back to rendering an error page as HTML.

Without @ResponseBody, Spring treats your return value as a view reference, not as data to serialize.

      │                        │
      ▼                        ▼
Returns view name        Returns JSON data
      │                        │
      ▼                        ▼
Spring finds template    Jackson serializes
      │                        │
      ▼                        ▼
HTML page                JSON string

How to Solve It?

There are three approaches.

Solution 1: Add @ResponseBody to method

@Controller
public class UserController {

    @GetMapping("/users")
    @ResponseBody
    public List&lt;User&gt; getUsers() {
        return userRepository.findAll();
    }
}

The @ResponseBody annotation tells Spring to serialize the return value directly to the response body using Jackson.

Solution 2: Use @RestController (recommended)

@RestController
public class UserController {

    @GetMapping("/users")
    public List&lt;User&gt; getUsers() {
        return userRepository.findAll();
    }
}

@RestController combines @Controller + @ResponseBody. All methods automatically return JSON.

Solution 3: Explicit produces attribute

@Controller
public class UserController {

    @GetMapping(value = "/users", produces = "application/json")
    @ResponseBody
    public List&lt;User&gt; getUsers() {
        return userRepository.findAll();
    }
}

The produces attribute explicitly declares the response Content-Type.

Now the response is proper JSON:

Content-Type: application/json;charset=UTF-8

Which Solution Should I Use?

└─────────────────────────┘
           │
           ▼
┌─────────────────────────┐
│ Use @RestController     │
│ (cleanest approach)     │
└─────────────────────────┘

┌─────────────────────────┐
│  Mixed controller?      │
│  (some HTML, some JSON) │
└─────────────────────────┘
           │
           ▼
┌─────────────────────────┐
│ Use @Controller +       │
│ @ResponseBody on JSON   │
│ methods                 │
└─────────────────────────┘

For a pure REST API, @RestController is the cleanest choice.

Common Mistakes

Mistake 1: Using @Controller for REST

@Controller  // Returns view names by default
public class ApiController {
    @GetMapping("/api/data")
    public Data getData() {  // Spring tries to find "Data" template
        return dataService.getData();
    }
}

Mistake 2: Double parsing in frontend

Angular HttpClient already parses JSON:

// Wrong: unnecessary double parse
data = JSON.parse(JSON.stringify(data));

// Right: Angular already parsed it
this.httpclient.get&lt;User[]&gt;('/api/users')
  .subscribe(users => {
    // users is already an array
  });

Mistake 3: Not checking Content-Type

Always verify your server sends the right Content-Type:

fetch('/api/users')
  .then(response => {
    const contentType = response.headers.get('content-type');
    if (!contentType?.includes('application/json')) {
      throw new Error('Expected JSON, got ' + contentType);
    }
    return response.json();
  });

Summary

In this post, I showed how to fix Spring Boot returning HTML instead of JSON. The key point is: use @RestController or add @ResponseBody to your methods. The frontend error “Unexpected token <” is a symptom—the real fix is on the server side.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Stack Overflow: Spring Boot HTML instead of JSON
👨‍💻 Spring Framework @RestController docs

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!