Service-to-service communication in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a RestTemplate bean for service communication.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

@Configuration
public class AppConfig {
    @Bean
    public RestTemplate [1]() {
        return new RestTemplate();
    }
}

Drag options to blanks, or click blank then click option'

ARestTemplate

BrestTemplate

CcreateRestTemplate

DgetRestTemplate

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase method name which is invalid in Java method naming conventions.

Using a name that does not match the bean usage elsewhere.

The method name restTemplate is the standard bean name for RestTemplate in Spring Boot.

2fill in blank

medium

Complete the code to send a GET request to another service using RestTemplate.

Spring Boot

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class UserService {
    @Autowired
    private RestTemplate restTemplate;

    public String getUserData() {
        String url = "http://userservice/api/users/1";
        return restTemplate.[1](url, String.class);
    }
}

Drag options to blanks, or click blank then click option'

Aexchange

BpostForObject

Cput

DgetForObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using postForObject which sends a POST request instead of GET.

Using put which is for updating resources.

getForObject sends a GET request and returns the response body converted to the specified class.

3fill in blank

hard

Fix the error in the RestTemplate call to send a POST request with a request body.

Spring Boot

public String createUser(String userJson) {
    String url = "http://userservice/api/users";
    return restTemplate.[1](url, userJson, String.class);
}

Drag options to blanks, or click blank then click option'

ApostForObject

BgetForObject

CgetForEntity

Dput

Attempts:

3 left

💡 Hint

Common Mistakes

Using getForObject which does not send a request body.

Using put which does not return a response body.

postForObject sends a POST request with a request body and returns the response body.

4fill in blank

hard

Fill both blanks to create a Feign client interface for service-to-service calls.

Spring Boot

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.[1];
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(name = "user-service")
public interface UserClient {
    @[2]("/api/users/{id}")
    String getUserById(@PathVariable("id") String id);
}

Drag options to blanks, or click blank then click option'

AGetMapping

BPostMapping

CRequestMapping

DDeleteMapping

Attempts:

3 left

💡 Hint

Common Mistakes

Using PostMapping for a GET request.

Using DeleteMapping which is for deleting resources.

Use @GetMapping annotation to define a GET request in Feign client.

5fill in blank

hard

Fill the two blanks to configure a WebClient bean with a base URL for service communication.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.reactive.function.client.WebClient;

@Configuration
public class WebClientConfig {
    @Bean
    public WebClient [1]() {
        return WebClient.builder()
            .baseUrl([2])
            .build();
    }
}

Drag options to blanks, or click blank then click option'

AwebClient

B"http://orderservice/api"

C"http://inventoryservice/api"

D"http://paymentservice/api"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method name casing.

Forgetting quotes around the base URL string.

The bean method is named webClient. The base URL is set to "http://orderservice/api".

Practice

1. What is the main purpose of service-to-service communication in Spring Boot microservices?

easy

A. To create user interfaces for microservices

B. To allow different microservices to exchange data and work together

C. To store data in a database

D. To compile Java code faster

Solution

1. Step 1: Understand microservices architecture

   Microservices are small services that work independently but often need to share data or trigger actions in other services.

2. Step 2: Identify the role of service-to-service communication

   This communication allows microservices to interact and cooperate by exchanging data or requests.

3. Final Answer:

   To allow different microservices to exchange data and work together -> Option B

4. Quick Check:

   Service communication = microservices working together [OK]

Hint: Microservices talk to each other to share data [OK]

Common Mistakes:

• Confusing service communication with UI creation
• Thinking it manages database storage
• Assuming it speeds up code compilation

2. Which of the following is the correct way to create a RestTemplate bean in Spring Boot for service-to-service calls?

easy

A. @Component
public void restTemplate() {
return new RestTemplate();
}

B. @Service
public RestTemplate restTemplate() {
return new RestTemplate();
}

C. @Bean
public RestTemplate restTemplate() {
return new RestTemplate();
}

D. RestTemplate restTemplate = new RestTemplate();

Solution

1. Step 1: Understand Spring bean creation

   To create a reusable RestTemplate, define a method annotated with @Bean inside a @Configuration class.

2. Step 2: Check the correct syntax

   @Bean public RestTemplate restTemplate() { return new RestTemplate(); } correctly uses @Bean and returns a new RestTemplate instance.

3. Final Answer:

   @Bean public RestTemplate restTemplate() { return new RestTemplate(); } -> Option C

4. Quick Check:

   @Bean method returns RestTemplate instance [OK]

Hint: Use @Bean to create reusable RestTemplate [OK]

Common Mistakes:

• Using @Service instead of @Bean
• Not returning RestTemplate instance
• Missing @Bean annotation

3. Given the following Spring Boot code snippet using WebClient, what will be the output if the called service returns "Hello from Service B"?

WebClient client = WebClient.create("http://service-b/api/greet");
String response = client.get()
    .retrieve()
    .bodyToMono(String.class)
    .block();
System.out.println(response);

medium

A. "Hello from Service B"

B. null

C. An exception is thrown

D. "Error: Service not found"

Solution

1. Step 1: Understand WebClient call

   The WebClient sends a GET request to the URL and retrieves the response body as a String.

2. Step 2: Analyze the response handling

   The block() method waits for the response synchronously and returns the body content.

3. Final Answer:

   "Hello from Service B" -> Option A

4. Quick Check:

   WebClient returns response body string [OK]

Hint: block() waits and returns response body string [OK]

Common Mistakes:

• Assuming asynchronous call returns immediately
• Expecting null without response
• Confusing error message with normal output

4. Identify the error in this Spring Boot service-to-service call using RestTemplate:

@Autowired
private RestTemplate restTemplate;

public String callService() {
    String url = "http://service-c/api/data";
    ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
    return response.getBody();
}

medium

A. getForEntity method does not exist

B. URL string is missing protocol

C. ResponseEntity cannot hold String type

D. RestTemplate bean is not defined in the configuration

Solution

1. Step 1: Check RestTemplate injection

   The RestTemplate must be defined as a bean for @Autowired to inject it properly.

2. Step 2: Verify URL and method usage

   The URL includes protocol and getForEntity is a valid method returning ResponseEntity<String>.

3. Final Answer:

   RestTemplate bean is not defined in the configuration -> Option D

4. Quick Check:

   Missing RestTemplate bean causes injection error [OK]

Hint: Always define RestTemplate as a @Bean before autowiring [OK]

Common Mistakes:

• Forgetting to create RestTemplate bean
• Using incomplete URL
• Misunderstanding getForEntity method

5. You want to call Service D from Service E using WebClient with a timeout of 2 seconds and handle errors gracefully. Which code snippet correctly implements this?

hard

A. WebClient client = WebClient.create("http://service-d/api");
String result = client.get()
.retrieve()
.bodyToMono(String.class)
.timeout(Duration.ofSeconds(2))
.onErrorReturn("Timeout or error")
.block();

B. WebClient client = WebClient.create();
String result = client.get()
.uri("http://service-d/api")
.retrieve()
.bodyToMono(String.class)
.block(Duration.ofSeconds(2));

C. RestTemplate restTemplate = new RestTemplate();
restTemplate.setTimeout(2000);
String result = restTemplate.getForObject("http://service-d/api", String.class);

D. WebClient client = WebClient.builder()
.baseUrl("http://service-d/api")
.build();
String result = client.get()
.retrieve()
.bodyToMono(String.class)
.block();

Solution

1. Step 1: Setup WebClient with timeout and error handling

   WebClient client = WebClient.create("http://service-d/api"); String result = client.get() .retrieve() .bodyToMono(String.class) .timeout(Duration.ofSeconds(2)) .onErrorReturn("Timeout or error") .block(); uses timeout(Duration.ofSeconds(2)) to limit wait time and onErrorReturn to provide fallback on errors.

2. Step 2: Verify other options

   WebClient client = WebClient.create(); String result = client.get() .uri("http://service-d/api") .retrieve() .bodyToMono(String.class) .block(Duration.ofSeconds(2)); but uses block(Duration) which times out and throws an exception instead of providing a fallback; RestTemplate restTemplate = new RestTemplate(); restTemplate.setTimeout(2000); String result = restTemplate.getForObject("http://service-d/api", String.class); tries to set timeout on RestTemplate incorrectly; WebClient client = WebClient.builder() .baseUrl("http://service-d/api") .build(); String result = client.get() .retrieve() .bodyToMono(String.class) .block(); lacks timeout and error handling.

3. Final Answer:

   WebClient client = WebClient.create("http://service-d/api"); String result = client.get() .retrieve() .bodyToMono(String.class) .timeout(Duration.ofSeconds(2)) .onErrorReturn("Timeout or error") .block(); -> Option A

4. Quick Check:

   Timeout + onErrorReturn = safe WebClient call [OK]

Hint: Use timeout() and onErrorReturn() for safe WebClient calls [OK]

Common Mistakes:

• Using block(Duration) which is invalid
• Trying to set timeout directly on RestTemplate
• Ignoring error handling in WebClient calls