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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.
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:
Get started with Spring and Spring Boot, through the Learn Spring course:
>> LEARN SPRINGExplore 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.
In this tutorial, we’ll look at how to set a custom header with the HttpClient.
If you want to dig deeper and learn other cool things you can do with the HttpClient – head on over to the main HttpClient tutorial.
We can set any custom header on a request with a simple setHeader call on the request:
@Test
void whenRequestHasCustomContentType_thenCorrect() throws IOException {
final HttpGet request = new HttpGet(SAMPLE_URL);
request.setHeader(HttpHeaders.CONTENT_TYPE, "application/json");
try (CloseableHttpClient client = HttpClients.createDefault()) {
String response = client.execute(request, new BasicHttpClientResponseHandler());
//do something with response
}
}As we can see, we’re setting the Content-Type directly on the request to a custom value – JSON.
With HttpClient 4.5 we can use RequestBuilder to set the header. To set a header, we’ll use the setHeader method – on the builder:
HttpClient client = HttpClients.custom().build();
HttpUriRequest request = RequestBuilder.get()
.setUri(SAMPLE_URL)
.setHeader(HttpHeaders.CONTENT_TYPE, "application/json")
.build();
client.execute(request);Instead of setting the Header on each and every request, we can also configure it as a default header on the Client itself:
@Test
void givenConfigOnClient_whenRequestHasCustomContentType_thenCorrect() throws IOException {
final HttpGet request = new HttpGet(SAMPLE_URL);
final Header header = new BasicHeader(HttpHeaders.CONTENT_TYPE, "application/json");
final List<Header> headers = Lists.newArrayList(header);
try (CloseableHttpClient client = HttpClients.custom()
.setDefaultHeaders(headers)
.build()) {
String response = client.execute(request, new BasicHttpClientResponseHandler());
//do something with response
}
}This is extremely helpful when the header needs to be the same for all requests – such as a custom application header.
This article illustrated how to add an HTTP header to one or all requests sent via the Apache HttpClient.
Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:
Once the early-adopter seats are all used, the price will go up and stay at $33/year.
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:
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:
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:
Get started with Spring Boot and with core Spring, through the Learn Spring course:
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.
