eBook – Guide Spring Cloud – NPI EA (cat=Spring Cloud)
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Let's get started with a Microservice Architecture with 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.

Get started with mocking and improve your application tests using our Mockito guide:

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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:

>> Download the eBook

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:

>> Join Pro and download the eBook

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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Get Started with Apache Maven:

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eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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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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Get started with Spring and Spring Boot, through the Learn Spring course:

>> LEARN SPRING
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:

>> The New “REST With Spring Boot”

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.

Get started with Spring Data JPA through the guided reference course:

>> CHECK OUT THE COURSE

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:

>> Learn Java Basics

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

1. Introduction

In this article, we’ll explore the differences between the Java Virtual Machine (JVM) and the Dalvik Virtual Machine (DVM). We’ll first take a quick look at each of them and then make a comparison.

Note that starting with Android 5.0, the Dalvik Virtual Machine has been replaced by Android Runtime (ART).

2. What Is a Runtime?

A runtime system provides an environment to translate the code written in a high-level language like Java to machine code and understandable by the Central Process Unit (CPU).

We can distinguish these types of translators:

  • Assemblers: They directly translate assembly codes to machine code so it is fast
  • Compilers: They translate the code into assembly code, then it uses assemblers to translate the resulting code into binary. Using this technique is slow but the execution is fast. Also, the resulting machine code is platform dependent
  • Interpreters: They translate the code while executing it. Since the translation happens at runtime, the execution may be slow

3. Java Virtual Machine

The JVM is a virtual machine to run Java desktop, server, and web applications. Another important thing about Java is it was developed with portability in mind. Thus, the JVM has been shaped also to support multiple host architectures and run everywhere. But, it is too heavy for embedded devices.

Java has an active community and will continue to be widely used in the future. Moreover, HotSpot is the JVM reference implementation. As well, there are also more than five other implementations maintained by the Open Source Community.

With the new cadence-based release, Java and the JVM are receiving new updates every six months. For example, we can list some proposals for the next releases such as Foreign-Memory Access and Packaging Tool.

4. Dalvik Virtual Machine

The DVM is a virtual machine to run Android applications. The DVM executes Dalvik bytecode, which is compiled from programs written in the Java language. Note that the DVM is not a JVM.

One of the key design principles of the DVM is that it should run on low memory mobile devices and loads quicker compared to any JVM. Also, this VM is more efficient when it runs multiple instances on the same device.

In 2014, Google released Android Runtime (ART) for Android 5 which replaced Dalvik for improved application performance battery usage. The last version was 1.6.0 on Android 4.4.

5. Difference Between JVM and DVM

5.1. Architecture

The JVM is a stack-based VM where all the arithmetic and logic operations are carried out via push and pop operands and results are stored on the stack. The stack is also the data structure to store methods.

Contrastingly the DVM is a register-based VM. These registers located in the CPU carry out all the arithmetic and logic operations. The register is the data structure to store operands.

5.2. Compilation

Java code is compiled inside the JVM to an intermediary format called Java bytecode (.class files). Then, the JVM parses the resulting Java bytecode and translates it to machine code.

On an Android device, the DVM compiles the Java code to an intermediate format called Java bytecode (.class file) like the JVM. Then, with the help of a tool called Dalvik eXchange or dx, it transforms Java bytecode to Dalvik bytecode. Finally, the DVM translates the Dalvik bytecode to binary machine code.

Both VMs use the Just-In-Time (JIT) Compiler. The JIT Compiler is a type of compiler that performs the compilation during the runtime.

5.3. Performance

As seen previously, JVM is a Stack-based VM and DVM is a Register-based VM. Stack-based VM bytecode is very compact because the location of operands is implicitly on the operand stack. Register-based VM bytecode requires all the implicit operands to be part of an instruction. That indicates that the Register-based code size will usually be much larger than Stack-based bytecode.

On the other hand, register-based VM’s can express computations using fewer VM instructions than a corresponding stack-based VM. Dispatching a VM instruction is costly, so the reduction in executed VM instructions is likely to significantly improve the speed of the register-based VM.

Of course, this distinction is only relevant when running the VM in interpreted mode.

5.4. Execution

Although it is possible to set up an instance of the JVM per running application, typically we’ll only configure one single instance of a JVM with shared processes and memory space to run all the applications we have deployed.

However, Android was designed to run multiple DVM instances. So to run an application or a service, the Android OS creates a new DVM instance with a separate process in shared memory space and deploys the code to run the application.

6. Conclusion

In this tutorial, we presented the main differences between the JVM and DVM. Both VM’s run applications written in Java, but they use different techniques and processes to compile and run code.

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)
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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:

>> 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?

Explore the eBook

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.

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