Top 5 Java Libraries You Need to Know

By NIIT Editorial

Published on 21/06/2023

Java libraries are collections of pre-written code that programmers may import into their Java programmes to accomplish a variety of tasks and operations. In order to save time and effort during development, developers may import these libraries into their projects and make use of their pre-written classes and methods.

There are several compelling arguments in favour of using Java libraries. For starters, it streamlines the development process by eliminating the need to rewrite commonly used features, freeing up more time to concentrate on what makes each application special. Second, libraries provide a tried-and-true method of solving common programming issues since they are often developed by industry professionals after extensive testing and optimisation. Last but not least, developers may take use of the rich ecosystem of open-source software and the comments and contributions of a sizable community by making use of existing libraries.


Table of Contents

  • Top 5 Java Libraries You Need to Know 
  • Comparison of the Top 10 Java Libraries 
  • How to Use Java Libraries 
  • Conclusion


Top 5 Java Libraries You Need to Know


1. Apache Commons

Apache Commons is a library of Java components that may be reused to provide new features to applications that are not included in the core Java libraries. I/O, collections, mathematics, and command line interface (CLI) tools are only some of the many categories of components included in this library.

The components available in Apache Commons are high-quality and open-source, making them ideal for use in Java development. These pre-built parts are meant to be reliable, well-tested, and efficient so that programmers don't have to start from scratch.

Apache Commons has a number of useful features, including:

  • Collections: The Java Collections Framework is enhanced by the Apache Commons library, which offers a variety of collection classes such as MultiMap and Bag.


  • I/O: File and stream manipulation, as well as archive management, are simplified using the I/O tools provided by Apache Commons.


  • CLI: A command-line interface (CLI) tool is available from Apache Commons, which makes it easier to develop CLIs for Java programmes.


  • Math: The mathematical tools included in Apache Commons span from complex number support to linear algebra to statistics.


  • Validation: Java programmes may make advantage of a collection of validation facilities provided by Apache Commons.


  • Text: The text utilities in Apache Commons allow you to deal with strings and regular expressions.

Java programmes may utilise Apache Commons Java classes and functions. These classes and methods can read and write files, work with collections, and validate input data.

Apache Commons lets developers focus on what makes their software unique rather than reinventing the wheel. Apache Commons is constantly updated to offer Java programmers with a high-quality, reliable library.


2. Log4j

To log messages from an application to different locations like files, databases, or syslog, developers may use Log4j, a Java-based logging tool. Developers may adjust various logging settings, such as log level, log format, and log destination, thanks to the system's adaptable configuration options.

Log4j's widespread adoption may be attributed to its user-friendliness, adaptability, and stability. Log4j's primary features consist of:

  • Log levels: Using Log4j, programmers may customise the logging depth depending on the importance of the logged information. Each of these levels—from TRACE to DEBUG to INFO to WARN to ERROR to FATAL—indicates the gravity of the message being sent.


  • Appenders: The destination of a log message may be specified using Log4j's Appender components. The destinations may be a file, a database, or something else.


  • Layouts: In order to format the log message, Log4j offers a collection of Layout components. Patterns, JSON, and XML are just some of the forms that may be used for these designs.


  • Filters: Filter components are available in Log4j and may be used to narrow down the log messages that are of interest.


  • Configuration: Log4j's configurable framework gives programmers granular control over their application's logging. An XML file, a properties file, or code may all be used to provide the settings.

Log4j's Java library can be simply incorporated into existing Java programmes, making it functional. These classes and methods let developers deliver application-generated log messages to text files, databases, and syslog.

Log messages include a message string and severity level. The developer chooses the recorded message text and severity level. An Appender component delivers the log message when it is produced.

Log4j lets programmers transmit application signals to several destinations without boilerplate code. Log4j's extensible configuration architecture lets developers customise application logging.

3. JUnit

Often used for unit testing Java applications, JUnit is a Java-based testing framework. It's an essential tool for Java programmers because of the streamlined process it streamlines for creating and executing unit tests.

JUnit's strength as a testing framework stems from a number of its notable characteristics. Some of these characteristics are:

  • Annotations: The JUnit framework has a collection of annotations for dictating the execution of tests. The @Test, @Before, @After, @BeforeClass, and @AfterClass annotations are examples of these.


  • Assert methods: To ensure that a test produces the desired results, you may utilise the assert methods that JUnit exposes. assertEquals(), assertTrue(), assertFalse(), assertNull(), and assertNotNull() are all examples of assert methods ().


  • Test Runners: In order to carry out tests, JUnit provides a collection of test runners. The JUnitCore, TextTestRunner, and SuiteRunner are all examples of such runners.


  • Parameterized Tests: The parameterized tests feature in JUnit enables developers to reuse testing methods while varying the input parameters.


  • Exception Testing: Using JUnit, developers can verify that an exception is raised only when it is expected to.

JUnit offers a Java library of classes and methods that may be imported into existing Java programmes. Developers may create unit tests using these classes and functions.

Developers create JUnit tests by creating a new class containing test methods. JUnit recognises @Test-annotated methods as test methods. Developers use assert methods in test methods to verify outcomes.

After developing the tests, JUnitCore or TextTestRunner may run them. The test runner runs and delivers the results.

JUnit lets programmers test their programmes and detect issues early. JUnit's easy-to-use unit test interface makes it essential for Java programmers.


4. Mockito

In order to test Java programmes, mock objects may be created and utilised Mockito, a popular mocking framework written in Java. It's a crucial tool for Java programmers because of the straightforward interface it offers for building fake objects.

Mockito's strength as a mocking framework stems from a number of its notable characteristics. Some of these characteristics are:

  • Creation of Mock Objects: Using Mockito, developers of Java programmes may quickly and simply generate fake objects for use in testing. Mock objects may be used to mimic the actions of their real-world counterparts in an application.


  • Stubbing Behaviour: Using Mockito, programmers may dictate how fake objects should respond to being invoked. This may be done by checking for the return of predetermined values, the occurrence of certain exceptions, or the invocation of specified methods.


  • Verification: Developers may use Mockito to ensure the application is operating as intended by checking that certain methods were called on the mock objects.


  • Argument Matching: Using Mockito, programmers can verify that mock objects accurately replicate real-world behaviour by matching inputs supplied to them.

Mockito offers Java classes and methods that may be smoothly incorporated into existing Java programmes. These classes and procedures allow developers to quickly create test objects.

Testing mock objects using Mockito.mock() is common. They may control the fake object using the when() and thenReturn() methods. Finally, developers may use verify() to verify that false object methods were called.

Mockito lets Java developers easily create false objects for testing. Simulating real-world behaviours may test their app's functioning. Java programmers need Mockito's simple interface for creating false objects.


5. Hibernate

Hibernate is an open-source Object Relational Mapping (ORM) framework written in Java that facilitates a quick and easy mapping of Java objects to relational database tables. It streamlines the application's data persistence layer so that developers may concentrate on the app's business logic rather than its database connection.

Hibernate is an effective ORM framework due to its many useful features. Some of these characteristics are:

  • Object-Relational Mapping: To lessen the amount of repetitive code needed for data persistence, developers may use Hibernate to map Java objects to relational database tables.


  • Query Language: Hibernate's Hibernate Query Language (HQL) is a robust query language that enables developers to build platform-independent SQL-like queries.


  • Lazy Loading: By minimising the number of times related objects need to be loaded from the database, Hibernate may help applications run faster.


  • Caching: To boost application speed, Hibernate has caching features that eliminate unnecessary database queries.


  • Transactions: Hibernate allows developers to partition their database operations into independent "transactions" that may be rolled back in the event of an error.

Hibernate provides a Java library for Java application development. These interfaces let programmers quickly link Java objects to relational databases and conduct SQL queries.

Developers construct Java classes for application entities before utilising Hibernate. These classes use Hibernate annotations to map database tables to Java objects.

The Hibernate API simplifies database record creation, modification, and deletion. Hibernate simplifies database storage by mapping Java objects to database tables.

Hibernate lets programmers simplify their data persistence layer and focus on business logic. Every Java programmer needs Hibernate because it simplifies mapping Java objects to relational database tables.


Comparison of the Top 5 Libraries

The advantages and disadvantages, as well as the most appropriate contexts, for using Apache Commons, Log4j, JUnit, Mockito, and Hibernate are outlined here.


1. Apache Commons:


  • Offers a large selection of Java components that may be utilised in a variety of contexts.
  • Provides commonly used programming jobs with pre-built components, reducing development time and effort.
  • Supported by a large group of programmers who work on it regularly.


  • It's possible that certain parts' functionality will overlap with that of Java's standard library.
  • It may take more time to learn how to use all the accessible parts since there are so many of them.


2. LOG4J:


  • Offers a logging framework that is both modifiable and adaptable for use in Java programmes.
  • Allows for output to a variety of formats, including the console, files, and databases.
  • Provides a variety of logging depths for improved logging customization by developers.


  • Larger projects can increase the difficulty of configuration.
  • If logging isn't streamlined, it might slow down the programme.




  • Offers a lightweight, straightforward framework for testing Java programmes.
  • Allows for test suites to be created and run in a predetermined sequence.
  • Tests may be conducted directly in the IDE thanks to its seamless integration with popular tools like Eclipse and IntelliJ.


  • More elaborate test cases can need more preparation.
  • It may take more work to integrate non-Java parts.


4. Mockito:


  • Offers a straightforward mimicking framework for testing Java programmes.
  • Allows for the generation of fake objects with arbitrary characteristics, as well as the validation of method invocations.
  • Provides seamless support for JUnit, making it simple to create and run tests.


  • More elaborate test cases can need more preparation.
  • If not done correctly, mocking may cause test cases to become unnecessarily complex.


5. Hibernate:


  • Gives Java developers access to a lightweight ORM framework.
  • Saves time by cutting down on repetitive code needed for saving data.
  • Includes transactional support, lazy loading, and caching to speed up your app.


  • Complex database schemas may need extra setup and configuration steps.
  • If optimisation steps are skipped or ignored, performance may suffer.


How to Use Java Libraries


1. Find the Appropriate Library 

Based on the needs of your project, choose the appropriate library.


2. Download the Library

Get the library and any other files it needs. Libraries and their required components are often made available via their own homepages or package managers.


3. Add the Library to Your Project 

Provide the library's location in your project's classpath or build system.


4. Import the Library

Use the relevant import lines to include the library into your code.


5. Use the Library 

To gain the necessary functionality, include the library's functions, classes, or methods into your code.


6. Test Your Code

To make sure the library is behaving as intended, you should test your code.


Common Mistakes to Avoid When Using Java Libraries:


1. Not Understanding the Library's Functionality

Before attempting to use the library, be sure you have a firm grasp on how it works. Mistakes may be avoided by reading the instructions or taking the lessons.


2. Not Updating the Library

Maintaining a library's up-to-date version gives you access to any recently added features or fixed bugs.


3. Using Outdated or Unsupported Libraries 

You should stay away from libraries that aren't being updated or that have security flaws.


4. Not Handling Exceptions

If you don't want your code to behave unexpectedly or crash, you should catch any exceptions produced by the library.


5. Over-Reliance on Libraries 

Don't put too much faith on libraries; they may not have the answer you're looking for. Always weigh the costs and benefits of utilising a library against writing your own solution.


6. Not Testing the Library

Before deploying the library in a live setting, make sure it functions as intended in a test environment.



In conclusion, Apache Commons is a library of Java components that can be reused, Log4j is a framework for logging messages from applications, JUnit is a testing framework that makes it easy to create and execute automated tests, Mockito is a popular mocking framework that helps programmers create more realistic simulations of real-world code, and Hibernate is an effective object-relational mapping tool that makes it simple to interact with databases.

Consider taking a Java developer course if you want to increase your knowledge of the language and your proficiency with Java libraries. Learning more about Java and how to leverage Java libraries to create stable, scalable applications is possible with the aid of these classes. In addition to providing you with access to industry professionals who can answer your questions and help you handle common issues, they can also provide you hands-on experience working with Java libraries.