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.
Get started with mocking and improve your application tests using our Mockito guide:
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:
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:
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:
Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:
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:
Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.
Get started with Spring Data JPA through the guided reference course:
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.
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:
1. Introduction
Quarkus is a Java framework that promises to deliver small artifacts, extremely fast boot time, and lower time-to-first-request. We achieve this by creating native images using GraalVM. When developing Quarkus applications, we may need access to resources such as text files that are bundled with the image or made available externally.
In this tutorial, we’ll examine different ways of making resources available to an application that is bundled as a Quarkus Native Image.
2. Project Configuration
We’ll create an example project to help us understand the different ways of loading resource files inside a Quarkus Native Image.
2.1. Creating a Project
We require a JDK and Quarkus CLI installed as prerequisites. Once the prerequisites are available, we can create a new project:
$ quarkus create app quarkus-resourcesThis should create a new project under the folder named quarkus-resources with basic scaffolding for a Quarkus project.
2.2. Dependencies
The project created using the quarkus CLI automatically adds core dependencies (quarkus-arc and quarkus-junit5) and dependencies for REST services (quarkus-rest, rest-assured). In addition, we need quarkus-rest-jackson for working with JSON in the input or output of the REST services:
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-arc</artifactId>
</dependency>
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-rest</artifactId>
</dependency>
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-rest-jackson</artifactId>
</dependency>
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-junit5</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>io.rest-assured</groupId>
<artifactId>rest-assured</artifactId>
<scope>test</scope>
</dependency>
3. Accessing Resources
Now that we have a project scaffolding ready, we’re ready to start accessing the resources through the code.
It’s important to note that GraalVM does not include any of the resources that are on the classpath into the native executable it creates. Resources that are meant to be part of the native executable need to be configured explicitly.
Quarkus provides us with a few different ways of accessing resources inside the application.
3.1. Public Resources
As with any Web application, we typically may need to expose some static web content such as HTML, JavaScript, and CSS. Quarkus automatically exposes the contents of META-INF/resources as web content.
We note that the META-INF/resources directory is meant for public resources only. We shouldn’t use this directory to put any non-public resources. This directory can be used to place all sorts of web content, but for our test, we placed a simple index.html inside this directory with the contents:
<!DOCTYPE html>
<html>
<head>
<title>Hello</title>
</head>
<body>
<h1>Hello from Baeldung!</h1>
</body>
</html>Then, we add a test to check the contents:
@Test
@DisplayName("should return content from index.html")
void givenIndexPage_whenGetRootUrl_thenReturnsContent() {
given()
.when().get("/")
.then()
.statusCode(200)
.body(containsString("Hello"));
}3.2. Property Configuration
We’ll create a couple of text files named default-resource.txt and text/another-resource.txt and place them under the resource directory src/main/resources. Unlike jar packaging, the contents of src/main/resources are not automatically present in the native image.
Therefore, we note that these resources need to be configured explicitly to be available in the code. This configuration can be added in application.properties as a comma-separated list of glob patterns:
quarkus.native.resources.includes=text/**,*.txtThen, we’ll create a method to allow us access to a given resource:
private String readResource(String resourcePath) throws IOException {
LOGGER.info("Reading resource from path: {}", resourcePath);
try (InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(resourcePath)) {
if (in == null) {
LOGGER.error("Resource not found at path: {}", resourcePath);
throw new IOException("Resource not found: " + resourcePath);
}
LOGGER.info("Successfully read resource: {}", resourcePath);
return new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8)).lines()
.collect(Collectors.joining("\n"));
}
}Finally, we’ll add a method to expose the contents of these resources through an API endpoint:
@GET
@Path("/default”)
@Produces(MediaType.TEXT_PLAIN)
public Response getDefaultResource() throws IOException {
return Response.ok(readResource("default-resource.txt")).build();
}
With that, we have successfully read the default-resource.txt from the classpath and exposed its contents through an API. In real projects, we’d perhaps use the contents differently. Next, we’ll use Junit for the test:
@Test
@DisplayName("should return content from default resource")
void whenGetDefaultResource_thenReturnsContent() {
given()
.when().get("/resources/default")
.then()
.statusCode(200)
.body(is("This is the default resource."));
}
3.3. Resource Configuration File
While the application.properties configuration offers a quick way to provide access to resources, sometimes the configuration can be more complex. In such a case, we may want to offer many different patterns to cover the files of interest.
GraalVM allows such configuration through the use of the resource-config.json:
{
"resources": [
{
"pattern": ".*\\.json$"
}
]
}We need to place this file under the folder src/main/resources/META-INF/native-image/<group-id>/<artifact-id>, and then the Quarkus build will take care of making the files available for use inside the code. Next, we create a separate endpoint to expose the contents of this file:
@GET
@Path("/json")
@Produces(MediaType.APPLICATION_JSON)
public Response getJsonResource() throws IOException {
return Response.ok(readResource("resources.json")).build();
}
Now we can test this:
@Test
@DisplayName("should return content from included json resource")
void whenGetJsonResource_thenReturnsContent() {
given()
.when().get("/resources/json")
.then()
.statusCode(200)
.body("version", is("1.0.0"));
}
So now we’ve successfully exposed resources using a resource-config file and patterns.
4. Manual Test of the APIs
We now have a few APIs that expose a few different resources, and we’ve written unit tests to check the expected output from the other API calls. We note, however, that Junit tests do not test the native image, and a true test of the availability of resources is to test the relevant API URLs from the native build.
Therefore, to properly test this, we can run a native build of the project:
$ mvn clean install -PnativeThis will create a native executable of the form <project-name>-<version>-runner under the target problem. We can run this executable and then test it using a browser or the curl command:
$ curl -X GET http://localhost:8080/resources/default
We expect this URL to return the contents of the default-resource.txt file. Similarly, we can also manually test the other URLs.
5. Conclusion
In this article, we configured an API using Quarkus and accessed file resources on the server using a Quarkus native image. We reviewed the different ways to access classpath resources from code. We need explicit configuration to access the resources on the classpath.
As always, the code is available over on GitHub.
