Content type negotiation in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the response content type when client requests JSON?

Given a Spring Boot controller method annotated with @GetMapping(produces = {"application/json", "application/xml"}), what content type will the server respond with if the client sends an Accept: application/json header?

Spring Boot

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

@RestController
public class MyController {
    @GetMapping(value = "/data", produces = {"application/json", "application/xml"})
    public Data getData() {
        return new Data("example", 123);
    }
}

record Data(String name, int value) {}

A The server responds with Content-Type: application/xml and XML formatted data.

B The server responds with Content-Type: application/octet-stream and binary data.

C The server responds with Content-Type: text/plain and plain text data.

D The server responds with Content-Type: application/json and JSON formatted data.

💡 Hint

Check the Accept header and the produces attribute in the controller.

The server uses content negotiation to match the client's Accept header with the produces types. Since the client requests application/json, the server responds with JSON.

📝 Syntax

intermediate

Which annotation correctly specifies multiple content types for response?

In Spring Boot, which of the following @GetMapping annotations correctly specifies that the method can produce both JSON and XML responses?

A @GetMapping(value = "/info", produces = "application/json, application/xml")

B @GetMapping(value = "/info", produces = {"application/json", "application/xml"})

C @GetMapping(value = "/info", produces = "application/json|application/xml")

D @GetMapping(value = "/info", produces = ["application/json", "application/xml"])

💡 Hint

Look at the correct Java array syntax for the produces attribute.

The produces attribute expects a String array. Option B uses the correct Java array syntax with curly braces and double quotes.

🔧 Debug

advanced

Why does the server respond with 406 Not Acceptable?

A client sends a request with header Accept: application/pdf to a Spring Boot endpoint that produces application/json only. What causes the 406 error?

Spring Boot

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

@RestController
public class PdfController {
    @GetMapping(value = "/report", produces = "application/json")
    public Report getReport() {
        return new Report("Monthly", 100);
    }
}

record Report(String title, int count) {}

A The server is down and returns 406 as a default error.

B The server has a syntax error in the controller method causing 406.

C The server cannot produce the requested content type application/pdf, so it returns 406 Not Acceptable.

D The client request is missing an Authorization header, causing 406.

💡 Hint

Think about what 406 status means in HTTP.

HTTP 406 means the server cannot generate a response matching the client's Accept header. Since the server only produces JSON and client wants PDF, it returns 406.

❓ state_output

advanced

What is the response content type if no Accept header is sent?

Consider a Spring Boot controller method annotated with @GetMapping(produces = {"application/json", "application/xml"}). If the client sends a request without an Accept header, what content type will the server respond with?

Spring Boot

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

@RestController
public class DefaultController {
    @GetMapping(value = "/default", produces = {"application/json", "application/xml"})
    public Info getInfo() {
        return new Info("default", true);
    }
}

record Info(String name, boolean active) {}

A The server responds with Content-Type: application/json by default.

B The server responds with Content-Type: application/xml by default.

C The server responds with Content-Type: text/html by default.

D The server responds with 406 Not Acceptable error.

💡 Hint

Think about the default content type Spring Boot uses when no Accept header is specified.

When no Accept header is sent, Spring Boot defaults to the first type listed in the produces array, which is usually JSON.

🧠 Conceptual

expert

How does Spring Boot determine response content type with multiple converters?

Spring Boot has multiple HttpMessageConverters registered, including JSON and XML converters. When a controller method produces both application/json and application/xml, how does Spring Boot decide which converter to use for the response?

A Spring Boot matches the client's Accept header with the supported media types of converters and picks the best match.

B Spring Boot always uses the JSON converter if available, ignoring the Accept header.

C Spring Boot uses the first registered converter regardless of the Accept header.

D Spring Boot randomly picks a converter from the registered list.

💡 Hint

Consider how HTTP content negotiation works with Accept headers and converters.

Spring Boot uses the Accept header to find the best matching media type among registered converters and uses that converter to serialize the response.