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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

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Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Baeldung)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat=Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag=Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

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.

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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:

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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:

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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 – All Access – NPI EA (cat= Spring)
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All Access is finally out, with all of my Spring courses. Learn JUnit is out as well, and Learn Maven is coming fast. And, of course, quite a bit more affordable. Finally.

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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:

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Partner – LambdaTest – NPI EA (cat=Testing)
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End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

>> Automated End-to-End Testing With Playwright

Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – Spring Sale 2025 – NPI (cat=Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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1. Overview

We often use maps to store a collection of key-value pairs. Then, at some point, we often need to iterate over them.

In this tutorial, we’ll compare different methods of map iteration, highlighting when it may be beneficial to use Map.Entry. Then, we’ll learn how Map.Entry can be used to create a tuple. Finally, we’ll create an ordered list of tuples.

2. Optimizing Map Iteration

Suppose that we have a map of book titles with the author’s name as the key:

Map<String, String> map = new HashMap<>();

map.put("Robert C. Martin", "Clean Code");
map.put("Joshua Bloch", "Effective Java");

Let’s compare two methods of getting all the keys and values from our map.

2.1. Using Map.keySet

First, consider the following:

for (String key : bookMap.keySet()) {
    System.out.println("key: " + key + " value: " + bookMap.get(key));
}

Here, the loop iterates over keySet. For each key, we get the corresponding value using Map.get. While this is an obvious way to use all of the entries in the map, it requires two operations for each entry — one to get the next key and one to look up the value with get.

If we need just the keys in a map, keySet is a good option. However, there’s a faster way to get both the keys and values.

2.2. Using Map.entrySet Instead

Let’s rewrite our iteration to use entrySet:

for (Map.Entry<String, String> book: bookMap.entrySet()) {
    System.out.println("key: " + book.getKey() + " value: " + book.getValue());
}

In this example, our loop is over a collection of Map.Entry objects. As Map.Entry stores both the key and value together in one class, we get them both in a single operation.

The same rules apply to using Java 8 stream operations. Streaming over the entrySet and working with Entry objects is more efficient and can require less code.

3. Working With Tuples

A tuple is a data structure that has a fixed number and order of elements. We can think of Map.Entry is a tuple that stores two elements – a key and a value. However, as Map.Entry is an interface, we require an implementation class. In this section, we’ll explore one implementation provided by the JDK: AbstractMap.SimpleEntry.

3.1. Creating a Tuple

First, consider the Book class:

public class Book {
    private String title;
    private String author;

    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }
    ...

Next, let’s create a Map.Entry tuple with the ISBN as the key and the Book object as the value:

Map.Entry<String, Book> tuple;

Finally, let’s instantiate our tuple with AbstractMap.SimpleEntry:

tuple = new AbstractMap.SimpleEntry<>("9780134685991", new Book("Effective Java 3d Edition", "Joshua Bloch"));

3.2. Creating an Ordered List of Tuples

When working with tuples, it’s often useful to have them as an ordered list.

First, we’ll define our list of tuples:

List<Map.Entry<String, Book>> orderedTuples = new ArrayList<>();

Secondly, let’s add some entries to our list:

orderedTuples.add(new AbstractMap.SimpleEntry<>("9780134685991", 
  new Book("Effective Java 3d Edition", "Joshua Bloch")));
orderedTuples.add(new AbstractMap.SimpleEntry<>("9780132350884", 
  new Book("Clean Code","Robert C Martin")));

3.3. Comparing With a Map

In order to compare the differences with a Map, let’s add a new entry with a key that already exists:

orderedTuples.add(new AbstractMap.SimpleEntry<>("9780132350884", 
  new Book("Clean Code", "Robert C Martin")));

Secondly, we’ll iterate over our list, displaying all the keys and values:

for (Map.Entry<String, Book> tuple : orderedTuples) {
    System.out.println("key: " + tuple.getKey() + " value: " + tuple.getValue());
}

Finally, let’s see the output:

key: 9780134685991 value: Book{title='Effective Java 3d Edition', author='Joshua Bloch'}
key: 9780132350884 value: Book{title='Clean Code', author='Robert C Martin'}
key: 9780132350884 value: Book{title='Clean Code', author='Robert C Martin'}

Notice that we can have duplicate keys, unlike a basic Map, where each key has to be unique. This is because we’ve used a List implementation to store our SimpleEntry objects, which means all the objects are independent of each other.

3.4. Lists of Entry Objects

We should note that the purpose of Entry is not to act as a generic tuple. Library classes often provide a generic Pair class for this purpose.

However, we may find that we need to temporarily work with lists of entries while preparing data for a Map or extracting data from one.

4. Conclusion

In this article, we looked at Map.entrySet as an alternative to iterating over a map’s keys.

We then looked at how Map.Entry can be used as a tuple.

Finally, we created a list of ordered tuples, comparing the differences to a basic Map.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
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.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat = Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag = Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

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?

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Course – LS – NPI EA (cat=REST)

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

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Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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Course – Spring Sale 2025 – NPI (All)
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Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:

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