How do you return JSON responses in Spring Boot?

Table of Contents

• Introduction
  • 1. Using **@RestController** for JSON Responses
    • Example: Using @RestController
  • 2. Using **@ResponseBody** for JSON Responses
    • Example: Using @ResponseBody
  • 3. Customizing JSON Serialization with Jackson
    • a. Using **@JsonProperty** for Custom JSON Keys
    • b. Using **@JsonIgnore** to Exclude Fields
  • 4. Handling HTTP Response Status Codes
    • Example: Using ResponseEntity for Custom Status Codes
  • 5. Testing JSON Responses
    • Example: Testing with curl
• 6. Conclusion

Introduction

In Spring Boot, returning JSON responses is a core functionality when building RESTful APIs. JSON is a common data format for communication between clients and servers in web applications. Spring Boot, through libraries like Jackson, automatically handles the conversion of Java objects to JSON and vice versa.

In this guide, we'll explore the various ways to return JSON responses in Spring Boot, including the use of annotations like @ResponseBody, @RestController, and others. We’ll also cover configuration steps for Jackson and practical examples.

1. Using **@RestController** for JSON Responses

One of the easiest and most common ways to return JSON in Spring Boot is by using the @RestController annotation. A @RestController is a specialized version of the @Controller annotation, which automatically applies @ResponseBody to all methods in the class. This eliminates the need to annotate each method with @ResponseBody.

Example: Using @RestController

In the above example:

• The method getProduct() returns a Product object.
• @RestController ensures the Product object is automatically converted into a JSON response by Spring Boot.

Example Response:

When you make a GET request to /product, Spring Boot automatically converts the Product object into JSON:

2. Using **@ResponseBody** for JSON Responses

In Spring Boot, you can use the @ResponseBody annotation to indicate that the return value of a controller method should be written directly to the HTTP response body, bypassing any view resolution. This is commonly used when you want to return JSON data from a method.

Example: Using @ResponseBody

In this example:

• The @ResponseBody annotation is applied to the getEmployee() method, which ensures that the returned Employee object is serialized into JSON.

Example Response:

When you make a GET request to /employee, the response will be:

3. Customizing JSON Serialization with Jackson

Spring Boot automatically configures Jackson as the default JSON serializer. However, you can customize how Java objects are serialized and deserialized by configuring Jackson annotations on your model classes.

a. Using **@JsonProperty** for Custom JSON Keys

In this case, the JSON output will use the custom keys "product_name" and "product_price":

b. Using **@JsonIgnore** to Exclude Fields

You can use @JsonIgnore to exclude specific fields from being included in the JSON response.

In this case, the JSON output will not include the price field:

4. Handling HTTP Response Status Codes

You can control the HTTP status code of the response using @ResponseStatus or ResponseEntity. By default, Spring Boot will return a 200 OK status for a successful request. However, you may need to return custom status codes for different scenarios.

Example: Using ResponseEntity for Custom Status Codes

In this example:

• The ResponseEntity allows you to return the response with both the data and a custom HTTP status code (e.g., HttpStatus.OK).

Example Response:

With a 200 OK status code.

5. Testing JSON Responses

You can test the JSON responses using tools like Postman or curl to ensure the proper content type is returned.

Example: Testing with curl

This will request the /product endpoint and expect a JSON response.

6. Conclusion

Returning JSON responses in Spring Boot is simple and efficient thanks to its built-in support for Jackson and annotations like @RestController and @ResponseBody. By default, Spring Boot automatically converts Java objects into JSON format and handles serialization for you. You can also customize the behavior using Jackson annotations, manage response status codes with ResponseEntity, and test your APIs with tools like Postman or curl.

Key takeaways:

• **@RestController** simplifies returning JSON in Spring Boot by applying @ResponseBody automatically to all methods.
• **@ResponseBody** can be used for direct data return, especially in REST APIs.
• Customize JSON output with Jackson annotations like @JsonProperty and @JsonIgnore.
• Control re.