eBook – Guide Spring Cloud – NPI EA (cat=Spring Cloud)
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eBook – Mockito – NPI EA (tag = Mockito)
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Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.

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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:

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eBook – Reactive – NPI EA (cat=Reactive)
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Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:

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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:

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eBook – Jackson – NPI EA (cat=Jackson)
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Do JSON right with Jackson

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eBook – HTTP Client – NPI EA (cat=Http Client-Side)
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Get the most out of the Apache HTTP Client

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eBook – Maven – NPI EA (cat = Maven)
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eBook – Persistence – NPI EA (cat=Persistence)
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eBook – RwS – NPI EA (cat=Spring MVC)
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Building a REST API with Spring?

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Course – LS – NPI EA (cat=Jackson)
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Course – RWSB – NPI EA (cat=REST)
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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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Course – LSS – NPI EA (cat=Spring Security)
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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.

You can explore the course here:

>> Learn Spring Security

Course – LSD – NPI EA (tag=Spring Data JPA)
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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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Partner – Moderne – NPI EA (cat=Spring Boot)
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Refactor Java code safely — and automatically — with OpenRewrite.

Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.

Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.

Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.

Course – LJB – NPI EA (cat = Core Java)
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Code your way through and build up a solid, practical foundation of Java:

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Partner – LambdaTest – NPI EA (cat= Testing)
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Distributed systems often come with complex challenges such as service-to-service communication, state management, asynchronous messaging, security, and more.

Dapr (Distributed Application Runtime) provides a set of APIs and building blocks to address these challenges, abstracting away infrastructure so we can focus on business logic.

In this tutorial, we'll focus on Dapr's pub/sub API for message brokering. Using its Spring Boot integration, we'll simplify the creation of a loosely coupled, portable, and easily testable pub/sub messaging system:

>> Flexible Pub/Sub Messaging With Spring Boot and Dapr

Partner – Diagrid – NPI (cat= Testing)
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Distributed systems often come with complex challenges such as service-to-service communication, state management, asynchronous messaging, security, and more.

Dapr (Distributed Application Runtime) provides a set of APIs and building blocks to address these challenges, abstracting away infrastructure so we can focus on business logic.

In this tutorial, we'll focus on Dapr's pub/sub API for message brokering. Using its Spring Boot integration, we'll simplify the creation of a loosely coupled, portable, and easily testable pub/sub messaging system:

>> Flexible Pub/Sub Messaging With Spring Boot and Dapr

1. Overview

Spring brings many features to help us with testing our code. Sometimes we need to use particular configuration properties in order to set up the desired scenario in our test cases.

In these situations, we can make use of the @TestPropertySource annotation. With this tool, we can define configuration sources that have higher precedence than any other source used in the project.

Hence, in this short tutorial, we’ll see examples where we use this annotation. Also, we’ll analyze its default behavior and the main attributes it supports.

To learn more about testing in Spring Boot, we suggest having a look at our ‘Testing in Spring Boot’ tutorial.

2. Dependencies

The easiest way to include all the required libraries in our project is by adding the spring-boot-starter-test artifact in our pom.xml file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

We can check Maven Central to verify we’re using the latest version of the starter library.

3. How to Use @TestPropertySource

Let’s imagine we’re using the value of a property by injecting it using the @Value Spring annotation:

@Component
public class ClassUsingProperty {
    
    @Value("${baeldung.testpropertysource.one}")
    private String propertyOne;
    
    public String retrievePropertyOne() {
        return propertyOne;
    }
}

We’ll then use the @TestPropertySource class-level annotation to define a new configuration source and override the value of that property:

@RunWith(SpringRunner.class)
@ContextConfiguration(classes = ClassUsingProperty.class)
@TestPropertySource
public class DefaultTest {

    @Autowired
    ClassUsingProperty classUsingProperty;

    @Test
    public void givenDefaultTPS_whenVariableRetrieved_thenDefaultFileReturned() {
        String output = classUsingProperty.retrievePropertyOne();

        assertThat(output).isEqualTo("default-value");
    }
}

Typically, whenever we use this test annotation we will also include the @ContextConfiguration one so as to load and configure the ApplicationContext for the scenario.

By default, the @TestPropertySource annotation tries to load a properties file relative to the class that declared the annotation.

In this case, for example, if our test class is in the com.baeldung.testpropertysource package, then we’ll need the file com/baeldung/testpropertysource/DefaultTest.properties in our classpath.

Let’s add it to our resources folder then:

# DefaultTest.properties
baeldung.testpropertysource.one=default-value

Additionally, we can change the default configuration file location, or add extra properties that will have even higher precedence:

@TestPropertySource(locations = "/other-location.properties",
  properties = "baeldung.testpropertysource.one=other-property-value")

It is possible to pass multiple custom properties. We can achieve this by using an array literal:

@TestPropertySource(
  locations = "/other-location.properties",
  properties = {
    "baeldung.testpropertysource.one=one",
    "baeldung.testpropertysource.two=two"
  }
)
public class MultiplePropertiesInPropertySourceTextBlockIntegrationTest {

With Java 15 and Spring 6.1.0, or newer, we have the option to use a multi-line text block:

@TestPropertySource(
  locations = "/other-location.properties",
  properties = """
    baeldung.testpropertysource.one=one
    baeldung.testpropertysource.two=two
    """)
public class MultiplePropertiesInPropertySourceTextBlockIntegrationTest {

Finally, we can specify whether we want to inherit locations and properties values from superclasses or not. Hence, we can toggle the inheritLocations and inheritProperties attributes, which are true by default.

4. Conclusion

With this simple example, we’ve learned how to use the @TestPropertySource Spring annotation effectively.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
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.

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:

>> Download the eBook

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)
announcement - icon

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:

>> CHECK OUT THE COURSE

Partner – Moderne – NPI EA (tag=Refactoring)
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Modern Java teams move fast — but codebases don’t always keep up. Frameworks change, dependencies drift, and tech debt builds until it starts to drag on delivery. OpenRewrite was built to fix that: an open-source refactoring engine that automates repetitive code changes while keeping developer intent intact.

The monthly training series, led by the creators and maintainers of OpenRewrite at Moderne, walks through real-world migrations and modernization patterns. Whether you’re new to recipes or ready to write your own, you’ll learn practical ways to refactor safely and at scale.

If you’ve ever wished refactoring felt as natural — and as fast — as writing code, this is a good place to start.

Course – LS – NPI – (cat=Spring)
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Get started with Spring Boot and with core Spring, through the Learn Spring course:

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eBook Jackson – NPI EA – 3 (cat = Jackson)