Spring Boot Interview Questions

Implementing versioning for RESTful web services in Spring Boot is crucial for maintaining backward compatibility and ensuring that changes in the API do not break existing clients. There are several strategies to implement versioning in RESTful services, each with its pros and cons. Here are some common approaches:

1. URI Versioning

In this approach, the version number is included in the URL path. It is simple and clear but can lead to URI clutter.

Example Implementation

@RestController
@RequestMapping("/api/v1")
public class UserControllerV1 {

    @GetMapping("/users/{id}")
    public UserV1 getUserById(@PathVariable("id") Long id) {
        return new UserV1(id, "John Doe");
    }
}

@RestController
@RequestMapping("/api/v2")
public class UserControllerV2 {

    @GetMapping("/users/{id}")
    public UserV2 getUserById(@PathVariable("id") Long id) {
        return new UserV2(id, "John Doe", "john.doe@example.com");
    }
}

class UserV1 {
    private Long id;
    private String name;

    // Constructors, getters, and setters
}

class UserV2 {
    private Long id;
    private String name;
    private String email;

    // Constructors, getters, and setters
}

2. Request Parameter Versioning

In this approach, the version number is passed as a request parameter. This keeps the URI clean but may not be as visible as URI versioning.

Example Implementation

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping(value = "/users/{id}", params = "version=1")
    public UserV1 getUserByIdV1(@PathVariable("id") Long id) {
        return new UserV1(id, "John Doe");
    }

    @GetMapping(value = "/users/{id}", params = "version=2")
    public UserV2 getUserByIdV2(@PathVariable("id") Long id) {
        return new UserV2(id, "John Doe", "john.doe@example.com");
    }
}

3. Header Versioning

In this approach, the version number is specified in a custom header. It keeps the URI clean but requires clients to set the correct headers.

Example Implementation

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping(value = "/users/{id}", headers = "X-API-VERSION=1")
    public UserV1 getUserByIdV1(@PathVariable("id") Long id) {
        return new UserV1(id, "John Doe");
    }

    @GetMapping(value = "/users/{id}", headers = "X-API-VERSION=2")
    public UserV2 getUserByIdV2(@PathVariable("id") Long id) {
        return new UserV2(id, "John Doe", "john.doe@example.com");
    }
}

4. Content Negotiation (Accept Header Versioning)

In this approach, the version number is included in the Accept header. This method leverages HTTP's content negotiation feature.

Example Implementation

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping(value = "/users/{id}", produces = "application/vnd.example.v1+json")
    public UserV1 getUserByIdV1(@PathVariable("id") Long id) {
        return new UserV1(id, "John Doe");
    }

    @GetMapping(value = "/users/{id}", produces = "application/vnd.example.v2+json")
    public UserV2 getUserByIdV2(@PathVariable("id") Long id) {
        return new UserV2(id, "John Doe", "john.doe@example.com");
    }
}

5. Using Media Types with Content Negotiation

In this approach, the versioning is handled through the Accept header by defining custom media types.

Example Implementation

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api")
public class UserController {

    @GetMapping(value = "/users/{id}", produces = "application/vnd.example.v1+json")
    public UserV1 getUserByIdV1(@PathVariable("id") Long id) {
        return new UserV1(id, "John Doe");
    }

    @GetMapping(value = "/users/{id}", produces = "application/vnd.example.v2+json")
    public UserV2 getUserByIdV2(@PathVariable("id") Long id) {
        return new UserV2(id, "John Doe", "john.doe@example.com");
    }
}

class UserV1 {
    private Long id;
    private String name;

    public UserV1(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getters and setters
}

class UserV2 {
    private Long id;
    private String name;
    private String email;

    public UserV2(Long id, String name, String email) {
        this.id = id;
        this.name = name;
        this.email = email;
    }

    // Getters and setters
}

Summary

• URI Versioning: Versions are included in the URL path. Simple and visible but can clutter URIs.
• Request Parameter Versioning: Versions are passed as query parameters. Keeps URI clean but less visible.
• Header Versioning: Versions are specified in custom headers. Requires clients to set headers correctly.
• Content Negotiation (Accept Header): Versions are specified in the Accept header. Uses HTTP content negotiation, keeping URI clean.

Each versioning strategy has its own advantages and trade-offs. The choice of strategy depends on the specific requirements of your API, client preferences, and the need for backward compatibility. Implementing these strategies in Spring Boot is straightforward with the use of annotations like @RequestMapping, @GetMapping, and the various HTTP headers.