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 short tutorial, we’ll have a quick overview of the memory types in the Java Virtual Machine (JVM).
The JVM uses different types of memory for different purposes, each with its own characteristics and behaviors. Understanding the different types of memory in JVM is important for designing efficient and stable applications.
2. Heap Memory
When the JVM starts up, it creates the heap memory. This memory type represents a crucial component of the JVM as it stores all the objects created by the application.
The size of the memory may increase or decrease while the application runs. However, we can specify the initial size of the heap memory using the -Xms parameter:
java -Xms4096M ClassNameFurthermore, we can define the maximum heap size using the -Xmx parameter:
java -Xms4096M -Xmx6144M ClassNameIf the application’s heap usage reaches the maximum size and it still requires more memory, it generates an OutOfMemoryError: Java heap space error.
3. Stack Memory
In this memory type, the JVM stores local variables and method information.
Furthermore, Java uses stack memory for thread execution. In an application, each thread has its own stack that stores information about the methods and variables it’s currently using.
However, it’s not managed by the Garbage Collection but by the JVM itself.
The stack memory has a fixed size, which is determined by the JVM at runtime. If the stack runs out of memory, the JVM throws the StackOverflowError error.
To avoid this potential problem, it’s essential to design the application to use the stack memory efficiently.
4. Native Memory
The memory allocated outside of the Java heap and used by the JVM is called native memory. It is also known by the term off-heap memory.
Since the data in native memory is outside the JVM, we need to perform serialization to read and write data. Performance depends on the buffer, serialization process, and disk space.
Additionally, due to its placement outside the JVM, it’s not freed up by the Garbage Collector.
In native memory, the JVM stores thread stacks, internal data structures, and memory-mapped files.
The JVM and native libraries use native memory to perform actions that can’t be accomplished entirely in Java, such as interacting with the operating system or accessing hardware resources.
5. Direct Memory
Direct buffer memory is allocated outside the Java heap. It represents the operating system’s native memory used by the JVM process.
Java NIO uses this memory type to write data to the network or disc in a more efficient way.
Because direct buffers aren’t freed up by the Garbage Collector, their impact on the memory footprint of an application might not be obvious. Therefore, direct buffers should be allocated primarily to large buffers that are used in the I/O operations.
To use a direct buffer in Java, we call the allocateDirect() method on ByteBuffer:
ByteBuffer directBuf = ByteBuffer.allocateDirect(1024);When loading files into memory, Java allocates a series of DirectByteBuffers using the direct memory. This way, it reduces the number of times the same bytes are copied. Buffers have a class responsible for freeing up the memory when the file is no longer needed.
We can limit the direct buffer memory size using the –XX:MaxDirectMemorySize parameter:
-XX:MaxDirectMemorySize=1024MIf native memory uses all the dedicated space for direct byte buffers, the OutOfMemoryError: Direct buffer memory error occurs.
6. Conclusion
In this short article, we learned about different memory types in JVM. In order to ensure the performance and stability of our applications, it’s helpful to understand the memory types in the JVM.
