Top 22 Java Libraries and APIs Every Programmer Should Learn in 2024
Most essential Java libraries you can learn to become a better Java developer. It includes Java libraries for logging, unit testing, mocking, networking, JSON, etc, and resources to learn them.
Hello Java programmers, if you are looking for the most essential Java libraries to learn and become a more competent Java developer in 2024 then you have come to the right place.
Earlier, I have shared essential Java Frameworks and the best courses to learn Spring Boot, one of the most popular Java frameworks and in this article, I am going to share the most popular and useful Java libraries you can learn to become a better Java programmer in 2024.
One of the traits of a good and experienced Java developer is the extensive knowledge of API, including JDK and third-party libraries. I spent a good deal of time learning API, especially after reading Effective Java 3rd Edition, where Joshua Bloch advised how to use existing APIs for development rather than writing new pieces of code for common stuff.
That advice made sense to me because of the testing exposure 2nd-party libraries get. In this article, I am going to share some of the most useful and essential libraries and APIs that a Java developer should be familiar with.
However, I am not including frameworks, Spring and Hibernate, because they are pretty well known and have specific features.
In general, I am including useful libraries for day-to-day projects, including logging libraries like Log4j, JSON parsing libraries like Jackson, and unit testing APIs like JUnit and Mockito.
If you need to use them in your project, then, you can either include JARs of these libraries in your project’s classpath to start using them or you can use Maven for dependency management.
When you use Maven for dependency management, it will automatically download these libraries, including the libraries they depend on, known as the transitive dependency.
For example, if you download the Spring Framework, it will also download all other JARs on which Spring is dependent, for example, Log4j.
You might not realize, but having the right version of dependent JARs is a big headache. If you have the wrong versions of the JAR, then, you will get the ClassNotFoundException, NoClassDefFoundError, or the UnsupportedClassVersionError in Java. If you have faced them before then you know how painful they are to solve.
20 Essential Libraries and APIs for Java Programmers in 2024
Here is my collection of some of the useful third-party libraries Java developers can use in their applications to do a lot of useful tasks. In order to use these libraries, Java developers should be familiar with them, and this is the whole point of this article. If you have an idea then you can research that library and use it.
1. Unit Testing Libraries [JUnit and Mockito]
Unit testing is the single most important thing that separates an average developer from a good developer. Programmers often are given excuses for not writing unit tests, but the most common excuse for avoiding unit testing is lack of experience and knowledge of popular unit testing libraries, including JUnit, Mockito, and PowerMock.
I always have a goal to improve my knowledge of unit testing and integration testing libraries, like JUnit 5, Cucumber, Robot framework, and a few others.
If you want to learn JUnit and Mockito and you need a resource, I highly recommend Learn Java Unit Testing with Junit & Mockito in 30 Steps by Ranga Karnam on Udemy. It’s a great, hands-on course to learn these useful libraries.
2. JSON Parsing libraries [Jackson and Gson]
In today’s world of web services and IoT, JSON has become the go-to protocol to carry information from the client to the server. They have replaced XML as the most preferred way to transfer information in a platform-independent way.
Unfortunately, JDK doesn’t have a JSON library. But, there are many good third-party libraries that allow you to both parse and create JSON messages, like Jackson and Gson.
A Java web developer should be familiar with at least one of these libraries. If you want to know more about Jackson and JSON, I suggest going through JSON with the Java API course from Udemy.
3. Logging Libraries [Log4j2 and SLF4j]
Logging libraries are very common because you need them in every project. They are the most important thing for server-side applications because logs are only placed where you can see what’s going on in your application.
Even though JDK ships with its own logging library, there are better alternatives available, like Log4j, SLF4j, and LogBack.
If you are interested to learn more bout logging in to Java then I highly recommend you Java Core Libraries: Java Log System course on Pluralsight.
This is a rare course to learn about when to use logging, why use logging, and how to generate useful log messages. It will also teach you how to use the Java Log System for logging and give you some back practices for logging in your application as well.
A Java developer should be familiar with the pros and cons of the logging library and know why using SLF4j is better than plain Log4j. If you don’t know why I suggest you read my earlier article on the same subject. I highly recommend this course to every Java developer.
By the way, you would need a Pluralsight membership to join this course which costs around $29 per month or $299 per year (14% discount). I highly recommend this subscription to all programmers as it provides instant access to more than 7000+ online courses to learn any tech skill. Alternatively, you can also use their 10-day-free-pass to watch this course for FREE.
4. General-Purpose Libraries [Apache Commons and Guava]
There is a couple of good, general-purpose, third-party libraries available to Java developers, like Apache Commons and Google Guava. I always include these libraries in my projects, because they simplify a lot of tasks.
As Joshua Bloch rightly said in Effective Java, there is no point in re-inventing the wheels. We should prefer using tried and tested libraries instead of writing our own routines every now and then.
It’s good for Java developers to get themselves familiar with Google Guava and the Apache Commons library.
5. HTTP Libraries [HttpClient]
One thing I don’t like about JDK is its lack of support for HTTP. Though you can make an HTTP connection using classes in the java.netpackage, it's not as easy or seamless to use open-source, third-party libraries like Apache HttpClient and HttpCore.
Though JDK 9 is bringing the support of HTTP 2.0 and better support for HTTP, I strongly suggest all Java developers get familiar with popular HTTP client libraries, including HttpClient and HttpCore.
You can also check out this post What’s New in Java 9 — Modules and More to learn more about JDK 9’s HTTP 2 support by Tim Buchalaka and his team on Udemy.
And, if you want to learn about the HttpClient in-depth, then I also recommend you to join Java Fundamentals: HttpClient course by Sander Mak. It’s a great course to learn this powerful API.
6. XML Parsing Libraries [Xerces and JAXB]
There are many XML parsing libraries, including Xerces, JAXB, JAXP, Dom4j, and Xstream. Xerces2 is the next generation of high-performance, fully compliant XML parsers in the Apache Xerces family.
This new version of Xerces introduces the Xerces Native Interface (XNI), a complete framework for building parser components and configurations that is extremely modular and easy to program.
The Apache Xerces2 parser is the reference implementation of XNI, but other parser components, configurations, and parsers can be written using the Xerces Native Interface.
Dom4j is another flexible XML framework for Java applications. If you want to learn more about XML parsing in Java, I suggest you take a look at the Java Web Services and XML online course on Udemy.
7. Excel Reading Libraries [Apache POI]
Believe it or not — all real-world applications have to interact with Microsoft Office in some form or another.
Many application needs to provide the functionality to export data in Excel, and if you have to do the same from your Java application, you need the Apache POI API.
This is a very rich library that allows you to both read and write XLS files from a Java program. You can see that link for a working example of reading an Excel file in a core Java application.
If you need a course or tutorial then you can also see this Create Advanced Excel files using Java, an Apache POI course on Udemy
8. Bytecode Libraries [Javassist and CgLib]
If you are writing a framework or libraries that generate code or interact with bytecodes, then, you need a bytecode library.
They allow you to read and modify the bytecode generated by an application. Some of the popular bytecode libraries in the Java world are javassist and Cglib Nodep.
The Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation very simple. It is a class library for editing bytecodes in Java. ASM is another useful bytecode editing library.
If you are not familiar with bytecode, I suggest you check the Java Programming Masterclass for Software Developers to learn more about it.
9. Database Connection Pool Libraries [DBCP and C3P0]
If you are interacting with the database from a Java application but not using database connection pool libraries, then, you are missing something.
Since creating database connections at runtime takes time and makes request processing slower, it’s always advised to use DB connection libraries. Some of the popular ones are Commons Pool and DBCP.
In a web application, its web server generally provides these functionalities, but in core Java applications, you need to include these connection pool libraries into your classpath to use the database connection pool.
If you want to learn more about JDBC and the connection pool in a web application, I suggest you take a look at the JSP, Servlets, and JDBC for Beginners: Build a Database App course by Chad Darby on Udemy.
10. Messaging Libraries [JMS and MQ]
Similar to logging and database connection, messaging is also a common feature of many real-world Java applications.
Java provides JMS or the Java Messaging Service, that’s not part of JDK. For this component, you need to include a separate jms.jar.
Similarly, if you are using third-party messaging protocols, like Tibco RV, then, you need to use a third-party JAR — tibrv.jar — in your application classpath.
If you want to learn more about JMS and need a resource then I highly recommend you to join the Java Message Service — JMS Fundamentals course by Bharat Thippireddy, one of my favorite Java instructors on Udemy.
11. PDF Libraries [iText]
Similar to Microsoft Excel, PDF libraries are another ubiquitous format. If you need to support PDF functionality in your application, like exporting data in PDF files, you can use the iText and Apache FOP libraries.
Both provide useful PDF-related functionality, but iText is richer and better. You can further see iText in Action book to learn more about iText.
12. Date and Time Libraries [Joda Time]
Before Java 8, JDK’s data and time libraries have so many flaws, because they were not thread-safe, immutable, and error-prone. Many Java developers relied on JodaTime for implementing their date and time requirements.
From JDK 8, there is no reason to use Joda, because you get all that functionality in the JDK 8’s new date and time API, but if you are working in an older Java version, then JodaTime is a worth learning library.
If you want to learn more about the new date and time API, I suggest you check the Java 8 New Features In Simple Way course on Udemy. It provides a nice overview of all the important features of Java 8, including the date and time API.
13. Collection Libraries [Eclipse Collections]
Even though JDK has a rich collection library, there are some 3rd-party libraries that provide more options, like the Apache Commons collections, Goldman Sachs collections, Google collections, Eclipse Collections, and Trove.
The Trove library is particularly useful because it provides high-speed regular and primitive collections for Java.
FastUtil is another similar API. It extends the Java Collections Framework by providing type-specific maps, sets, lists, and priority queues with a small memory footprint, fast access, and insertion; it also provides big (64-bit) arrays, sets, and lists, with fast, practical I/O classes for binary and text files.
Eclipse Collections is another useful open-course collections library that is worth learning. By the way, if you want to learn more about Java Collections, you can also check out Java Collections from basics to Advanced courses on Udemy.
14. Email APIs [Java Mail API]
The javax.mail and Apache Commons Email both provide an API for sending an email from Java. It is built on top of the JavaMail API, which it aims to simplify.
If you need a project, you can build an email client using Java FX and use mail API there to send mails.
If you need help, you can also check out Advanced Java programming with JavaFx: Write an email client course on Udemy
15. HTML Parsing Libraries [Jsoup]
Similar to JSON and XML, HMTL is another common format many of us have to deal with. Thankfully, we have JSoup, which greatly simplifies working with HTML in a Java application.
You can use JSoup to not only parse HTML but also to create HTML documents
It provides a very convenient API for extracting and manipulating data, using the best of DOM, CSS, and jquery-like methods. JSoup implements the WHATWG HTML5 specification and parses HTML to the same DOM, as modern browsers do.
16.Cryptographic Library
The Apache Commons Codec package contains simple encoders and decoders for various formats, such as Base64 and Hexadecimal.
In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
17. Embedded SQL Database Library [H2, HSQL, and Derby]
I really love in-memory databases like H2, which you can embed in your Java application. They are great for testing your SQL scripts and running unit tests that need a database.
However, H2 is not the only DB, you also have Apache Derby and HSQL to choose from.
18. JDBC Troubleshooting Libraries
There are some good JDBC extension libraries that exist and can make debugging easier, like the P6spy.
This is a library that enables database data to be seamlessly intercepted and logged with no code changes to the application. You can use these to log SQL queries and their timings.
For example, if you are using PreparedStatment and CallableStatement in your code, these libraries can log an exact call with parameters and how much time it took to execute.
If you want to learn more about JDBC, you can check out the Complete JDBC Programming Part-1 course on Udemy.
19. Networking Libraries [Apache MINA]
Some of the useful networking libraries are Netty and Apache MINA. If you are writing an application where you need to do low-level networking tasks, consider using these libraries.
If you want to learn more about networking programming in Java, check out this Programming Network application in Java course on Udemy. It’s a really nice course to learn TCP, UDP, and other networking fundamentals from a Java programming perspective.
20. Lombok [Project Lombok]
This is another awesome Java library you should learn in 2024 as it makes working with Java really fun by removing the boilerplate coding. For example, you can declare your Java class with just fields with getter and setter and it looks really clean as shown in this Lombok example.
You can instruct Lombok to create common methods like equals and hashcode, toString, getter, and setters as well you can also put assertions like NonNull for robust coding. All that can be done by adding just a few annotations like @ToString, @EQualsAndHashCode, @NonNull, etc.
You can also create builder and constructor using Lombok by using @Builder annotation and then there is @Data annotation which automatically applies common annotations ot make your code even cleaner.
Here is a class that is declared using Lombok, you can see that its much cleaner than traditional POJO (Plain Old Java Object]
21. Testcontainers
This is another awesome Java library that every Java developer should learn in 2024. If you don’t know, Tescontainer is a Java library that supports JUnit tests, providing lightweight, throwaway instances of common databases, Selenium web browsers, or anything else that can run in a Docker container.
If you are wondering why do we use Testcontainers or why do we need it then let me tell you that Testcontainers will allow us to write integration tests making use of containerized databases, message queues, web browsers, etc. without a dependency on a local installation
It really makes testing setup easier than ever before, particularly for testing spring boot applications. If you want to learn more about testing the spring boot apps using test contains then I suggest you join Spring Boot Testing Masterclass by RieckPil, one of my favorite courses to learn advanced testing stuff for Java developers.
This course will teach you everything you need to know about testing the spring boot app, including test containers. You can also use my code TSBAX_M2LAP to get a 10% discount.
Here is the link to join this course: Spring Boot Testing Masterclass
22. Serialization Libraries [Google Protocol Buffer]
The Google Protocol Buffers are a way of encoding structured data in an efficient — yet, extensible — format. It’s a richer and better alternative to Java serialization.
I strongly recommend experienced Java developers to learn Google Protobuf. You can see this article to learn more about the Google Protocol Buffer.
And, if you need a resource to learn Google Protocol Buffer then I highly recommend you to join Complete Guide to Protocol Buffers 3 [Java, Golang, Python] course by
on Udemy. It’s a really nice and up-to-date resource to learn Google Protocol buffer.
That’s all for now about some of the useful libraries every Java developer should be using. The Java sphere is vast, and you will find tons of libraries for doing different things.
If you want to do anything in Java, more than likely, you will find a library on how to do just that. As always, Google is your best friend to find useful Java libraries, but you can also take a look at the Maven central repository to find some of the useful libraries for your task at hand.
If you like this article, you may find my other articles useful too:
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- 10 Best Courses to learn Spring and Hibernate
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- 21 Java Books You Can Read in 2024
- 15 Things Java Developer Should Learn in 2024
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- 21 Books Java Developers should read in 2024
- 10 Pluralsight Courses for Java and Web Developers
- 10 Tutorials to Learn Java 8 Better
- 10 tips to become a better Java Programmer
- 10 Tools Java Developer Should Learn in 2024
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P.S. — And, if you want to take your Java programming skills to next level and want to learn Java in-depth then I suggest you check out this list of advanced Java Programming courses, which contain a list of the most advanced courses. It’s updated to cover features of recent Java features.
