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20 Useful Open Source Libraries for Java Programmers
1. JSON Libraries
JSON parsing libraries in the modern era of information technology, JSON plays a very important role as it is a medium to transfer information from the client to the server. The traditional XML’s parsing which was platform-dependent has been replaced with JSON as it is platform-independent.
Currently, Java Development Kit does not yet have a JSON library but many other useful third-party libraries are available which can help you parse as well as create JSON messages just like Gson or Jackson.
2. Unit testing libraries
The most important part of the development lifecycle is Unit Testing. This separates an average programmer from a good programmer. Most of the programmers have trouble writing unit test cases as they mostly are unaware of the popular testing libraries of JAVA which can benefit them in writing error-free code before they pass it for QA. Some of the most widely used libraries are Mockito, PowerMock, JUnit, etc which allow programmers to test their code with desired inputs and see the results.
3. Logging libraries
Logging libraries are important for applications which have a server-side as they help you see how your application is running. Identifying errors and their resolution becomes easy if logging is done effectively within the application. JDK has its own logging library but many other useful libraries like SLF4j, LogBack, and Log4j can be used for better approaches and results.
4. HTTP libraries
Most of the JDKs do not support HTTP which is a great drawback. Although the HTTP connection can be made using the java.net package classes it is not an easy and effortless task as compared to using open-source third-party libraries like HttpCore and Apache HttpClient.
JDK 9 has support for HTTP 2.0 so the developers should be aware of famous HTTP client libraries including HttpCore and HttpClient.
5. XML parsing libraries
Many XML parsing libraries are available in JAVA which can be used as per the requirements. Some of the libraries are Dom4j, JDom, Stax, JaxB, Xerces, etc.
Dom4j is the most popular of all the libraries when working with XML files as it allows bi-directional reading, create as well as update the documents easily but they are expensive on the memory side. JDom is very similar to Dom 4j and retrieving information in JDom is easy.
Stax does not allow bi-directional navigation and retrieval of information is not easy whereas JAXB is very easy to load, produce and information from an XML file can be manipulated easily. Just correct java entities are to be created and then bind the XML to them.
Xerces2 is the most advanced, high performance and fully compliant XML parser among all the Apache Xerces family. The new version has ‘XNI’ which is a complete framework for parser components building and configurations and is very easy to program.
6. General-purpose libraries
There are some very useful general-purpose third party libraries which can simplify a lot of jobs. Some of such common libraries are Google Guava and Apache Commons. Instead of writing your own routines every time, you can use these libraries which have been tested and work perfectly and thus save your time and effort.
7. Bytecode libraries
If you are working on a task that requires writing a framework or need any library which interacts with bytecodes or generates code then the bytecode library can serve your purpose. They allow you to read and alter the bytecode generated by any application. The most common bytecode libraries are Cglib Nodep, ObjectWeb ASM, javascript, etc.
ASM is a very useful library to edit bytecode. Javassit is one of the most widely used bytecode libraries through which manipulation of bytecodes becomes easy.
8. Messaging libraries
Messaging is a very common and widely used feature in many Java applications. Java has a library called JMS (Java Messaging Service) but it is not integrated with the JDK. In order to use it, you have to include jms.jar in your project. There are other third-party protocols named Tibco RV for messaging which can be used by including its JAR named tibrv.jar in your application.
9. Microsoft Excel reading libraries
Most of the real-world applications use Microsoft office which includes xls or csv file generation and reading. Data export in applications is usually done in Excel because it is readable and easy to manage. In order to generate excels in Java an API named Apache POI API can be used which is flexible and easy to use. It can aid you in both reading and writing files from Java with simple implementation steps.
10. PDF Libraries
Just like Word and Excel, PDF format is widely used in real-world applications. You can have PDF functionality of exporting files in PDF format by using Apache FOP and iText libraries. Both of these support it but iText is simpler, sophisticated, and rich in functionality so it is used as a preference.
11. Database connection pool libraries
There are a few Java database connection pool libraries through which the database operations can be performed swiftly. Creating connections during runtime makes the request-response slower as the connection requires time. Therefore it is advised to use DB connection libraries named DBCP and Common Pool available.
In order to use these libraries, you will have to include connection pool libraries in the classpath of Java and then you will be able to use the database connection pool.
12. Collection libraries
Although JDK has many collection libraries some of the available 3rd party libraries are available which can be included in your project easily and provide many useful options. The libraries include Goldman Sachs collections, Eclipse Collections, Google Collections, Trove, and Apache Commons Collections. Each of these libraries provides a wide variety of functionalities that you can use to accomplish your tasks. Trove is popular as it is efficient and provides systematic and primeval collections of Java.
13. Email APIs
The Apache Commons Email and javax.mail offers an API through which you can send emails. It has been built using JavaMail API which has been used to simplify the process.
14. Date and Time libraries
Initially, date and time libraries such as Joda had many flaws as they were not error-prone, thread-safe, and absolute. JDK 8 has introduced its own Date and Time API to manipulate your date-time functions easily. The fundamental classes in the java.time package use ISO-8601 calendar system which is by default based on the Gregorian calendar system.
15. Cryptographic library
In order to use cryptography techniques in Java, the Developers should be aware of cryptographic libraries of the programming language and platform. You should have an understanding of all the basic concepts of cryptography as any loophole may expose your system to potential risks. The Apache Commons Codec package has a very simple encoder as well as decoders for Base64 and hexadecimal formats. There are many other libraries like Bouncy Castle, JCA, and Web3j out of which Bouncy Castle is leading.
16. HTML Parsing libraries
HTML is a common format that is widely used in many applications. Java has JSOUP which is a powerful library to extract data from HTML. You can manipulate as well as generate HTML as an output using it. It uses the best CSS, DOM, and jquery methods. It forms a tree just like DOM in the browser and offers methods to manipulate HTML/text/attributes and add as well as remove elements.
17. JDBC Troubleshooting libraries
Debugging is an important aspect of programming. There are certain JDBC libraries that make this easier and stress-free. P6sy is a useful library that enables you to intercept and log databases easily with no code modifications. Using it, you can log timings of SQL queries seamlessly. You can log the exact call/method and time that it took to execute to improve the performance of your application.
18. Embedded SQL database library
Embedded SQL database means that it is an inseparable part of software application. A very common in-memory database is H2 which can be easily embedded in your Java application. They can be useful in Unit testing and running scripts that involve database involvement. There are other databases like HSQL and Apache Derby which can be used as embedded SQL.
19. Networking libraries
Networking is basically running programs on different computers. Some useful libraries of networking are Apache MINA and Netty. If low-level networking is required these libraries can serve your purpose. Apache MINA can be used to create high-performance scalable networks.
20. Serialization libraries
Java provides a method of serialization through which the object can be written in the form of bytes. The impressive thing is that the process is JVM independent. The object can be serialized on one platform and deserialized on a different platform. Azrael is a popular library of Java for serialization. It allows you to store the java object information in one data format and deserialize it later to some other format. Protobuf is also a way of encoding data in an extensible format and is more efficient.