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. Overview
In this quick tutorial, we will discuss the performance improvements that come along with the latest Java 10 release.
These improvements apply to all applications running under JDK 10, with no need for any code changes to leverage them.
2. Parallel Full GC for G1
The G1 garbage collector is the default one since JDK 9. However, the full GC for G1 used a single threaded mark-sweep-compact algorithm.
This has been changed to the parallel mark-sweep-compact algorithm in Java 10 effectively reducing the stop-the-world time during full GC.
3. Application Class-Data Sharing
Class-Data Sharing, introduced in JDK 5, allows a set of classes to be pre-processed into a shared archive file that can then be memory-mapped at runtime to reduce startup time which can also reduce dynamic memory footprint when multiple JVMs share the same archive file.
CDS only allowed the bootstrap class loader, limiting the feature to system classes only. Application CDS (AppCDS) extends CDS to allow the built-in system class loader (a.k.a., the “app class loader”), the built-in platform class loader, and custom class loaders to load archived classes. This makes it possible to use the feature for application classes.
We can use the following steps to make use of this feature:
1. Get the list of classes to archive
The following command will dump the classes loaded by the HelloWorld application into hello.lst:
$ java -Xshare:off -XX:+UseAppCDS -XX:DumpLoadedClassList=hello.lst \
-cp hello.jar HelloWorld2. Create the AppCDS archive
Following command creates hello.js a using the hello.lst as input:
$ java -Xshare:dump -XX:+UseAppCDS -XX:SharedClassListFile=hello.lst \
-XX:SharedArchiveFile=hello.jsa -cp hello.jar3. Use the AppCDS archive
Following command starts the HelloWorld application with hello.jsa as input:
$ java -Xshare:on -XX:+UseAppCDS -XX:SharedArchiveFile=hello.jsa \
-cp hello.jar HelloWorldAppCDS was a commercial feature in Oracle JDK for JDK 8 and JDK 9. Now it is open sourced and made publicly available.
4. Experimental Java-Based JIT Compiler
Graal is a dynamic compiler written in Java that integrates with the HotSpot JVM; it’s focused on high performance and extensibility. It’s also the basis of the experimental Ahead-of-Time (AOT) compiler introduced in JDK 9.
JDK 10 enables the Graal compiler, to be used as an experimental JIT compiler on the Linux/x64 platform.
To enable Graal as the JIT compiler, use the following options on the java command line:
-XX:+UnlockExperimentalVMOptions -XX:+UseJVMCICompilerNote that this is an experimental feature and we may not necessarily get better performance than the existing JIT compilers.
5. Conclusion
In this quick article, we focused on and explored the performance improvement features in Java 10.
