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Partner – Microsoft – NPI EA (cat = Baeldung)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat=Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

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Partner – Orkes – NPI EA (tag=Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

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Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

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Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.

I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.

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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.

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End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

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1. Introduction

Spring’s validation framework is primarily designed to work with JavaBeans, where each field can be annotated with validation constraints. ​

In this tutorial, we’ll explore how to validate a Map<String, String> using Spring’s Validator interface. This approach is particularly useful when dealing with dynamic key-value pairs that don’t map directly to a predefined Java object.

2. Understand the Problem – Hibernate Validator and Maps

Before implementing a custom validator, it’s natural to try and apply standard constraint annotations directly on the map structure using Hibernate Validator and Spring’s built-in validation mechanisms like @Valid and @Validated. Unfortunately, this approach doesn’t work as we might expect.

Let’s look at an example:

Map<@Length(min = 10) String, @NotBlank String> givenMap = new HashMap<>();
givenMap.put("tooShort", "");

Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
Set<ConstraintViolation<Map<String, String>>> violations = validator.validate(givenMap);
        
Assertions.assertThat(violations).isNotEmpty(); // this will fall

Despite the annotated type parameters, the violations set will be empty — no constraint violations will be detected.

2.1. Why This Fails?

Hibernate Validator, or Bean Validation in general, operates based on JavaBeans conventions, meaning it validates object properties accessible via getters. Since maps don’t expose keys and values as properties, constraint annotations like @Length or @NotBlank aren’t directly applicable and are ignored during validation.

In other words, from the validator’s perspective, a map is a black box — it doesn’t know how to introspect its contents unless explicitly told how.

2.2. When Does It Work?

Type-level constraint annotations can work when a map is a property within a JavaBean, like so:

public class WrappedMap {
    private Map<@Length(min = 10) String, @NotBlank String> map;

    // constructor, getters, setters...
}

This works thanks to support for container element constraints in Hibernate Validator. However, validation of both keys and values is still limited and inconsistent, especially for maps. You may need to explicitly enable value extractors, and even then, full support isn’t guaranteed.

To address this limitation, we can create a custom validator by implementing the Validator interface provided by Spring.

3. Project Configuration

Before implementing our solution, we need to configure the project with the necessary dependencies. If we’re using Spring Boot, everything is included in a single starter:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
    <version>3.4.5</version>
</dependency>

However, if we’re working with plain Spring Framework, you’ll need to include the Jakarta Validation API and its Hibernate implementation manually:

<!-- Core Spring Framework -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>6.2.6</version>
</dependency>

<!-- Validation related -->
<dependency>
    <groupId>jakarta.validation</groupId>
    <artifactId>jakarta.validation-api</artifactId>
    <version>3.1.1</version>
</dependency>
<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>8.0.2.Final</version>
</dependency>

These dependencies enable us to implement and use a custom Validator for our map structure.

4. Implementing the Custom Validator

Once the project is set up, we can proceed to implement the custom validator. We’ll replicate the validation rules from the earlier code snippet, checking both the keys and the values:

@Service
public class MapValidator implements Validator {
    @Override
    public boolean supports(Class<?> clazz) {
        return Map.class.equals(clazz);
    }

    @Override
    public void validate(Object target, Errors errors) {
        Map<?, ?> rawMap = (Map<?, ?>) target;

        for (Map.Entry<?, ?> entry : rawMap.entrySet()) {
            Object rawKey = entry.getKey();
            Object rawValue = entry.getValue();

            if (!(rawKey instanceof String key) || !(rawValue instanceof String value)) {
                errors.rejectValue("map[" + rawKey + "]", "map.entry.invalidType", "Map must contain only String keys and values");
                continue;
            }

            // Key validation
            if (key.length() < 10) {
                errors.rejectValue("map[" + key + "]", "key.tooShort", "Key must be at least 10 characters long");
            }

            // Value validation
            if (!StringUtils.hasText(value)) {
                errors.rejectValue("map[" + key + "]", "value.blank", "Value must not be blank");
            }
        }
    }
}

This class implements Spring’s Validator interface, which requires two methods:

  • supports(Class<?> clazz) – determines whether this validator can handle the given class
  • validate(Object target, Errors errors) – performs the actual validation and reports any constraint violations

Note that we explicitly check the type of keys and values to ensure type safety and avoid ClassCastException at runtime.

5. Calling the Validator

Spring’s validation framework integrates smoothly with service classes, allowing us to create reusable code, inject it, and use our custom validator wherever it’s needed.

We can now inject and use your custom validator inside any Spring-managed service:

@Service
public class MapService {
    private final MapValidator mapValidator;

    @Autowired
    public MapService(MapValidator mapValidator) {
        this.mapValidator = mapValidator;
    }

    public void process(Map<String, String> inputMap) {
        // Wrap the map in a binding structure for validation
        MapBindingResult errors = new MapBindingResult(inputMap, "inputMap");

        // Run validation
        mapValidator.validate(inputMap, errors);

        // Handle validation errors
        if (errors.hasErrors()) {
            throw new IllegalArgumentException("Validation failed: " + errors.getAllErrors());
        }
        // Business logic goes here...
    }
}

This example shows how the MapValidator can be injected using constructor injection and invoked before executing core business logic. Wrapping the map in a MapBindingResult allows Spring to collect and structure validation errors consistently.

6. Conclusion

Validating Map<String, String> structures in Spring requires a custom approach, as standard validation mechanisms don’t introspect map contents by default. Support for Bean Validation is limited and might not work as we expect.

By implementing the Validator interface and integrating it into your service layer, we gain full control over how each key-value pair is validated, making our application both more robust and more flexible. This strategy is especially helpful when dealing with dynamic inputs like configurations, user-defined forms, or third-party JSON structures.

As always, all the code examples used in this article and even more examples are available over on GitHub.

Baeldung Pro – NPI EA (cat = Baeldung)
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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat = Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag = Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

eBook – HTTP Client – NPI EA (cat=HTTP Client-Side)
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The Apache HTTP Client is a very robust library, suitable for both simple and advanced use cases when testing HTTP endpoints. Check out our guide covering basic request and response handling, as well as security, cookies, timeouts, and more:

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eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

>> Download the eBook

eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

>> Join Pro and download the eBook

eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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Course – LS – NPI EA (cat=REST)

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Get started with Spring Boot and with core Spring, through the Learn Spring course:

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Partner – Microsoft – NPI (cat=Spring)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

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