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Tuesday, February 9, 2021

Top 5 JSON Library Java JEE Developers Should Know- Best of Lot

The JSON format is one of the most popular formats to transfer and exchange data on the web. Almost all RESTful web services take JSON input and provide JSON output but unfortunately, JDK doesn't have built-in support for one of the most common web standards like JSON. As a Java developer if you want to develop a RESTful web service and produce JSON data or if you are developing a client to existing RESTFul web services and want to consume JSON response, you don't need to be disappointed. Fortunately, there are so many open source libraries and APIs available for creating, parsing, and processing JSON response in Java, like Jackson, Google GSon, json-simple, etc.

Actually, there are numerous JSON libraries that exist in Java but you don't need to learn all of them, learning just one of them like Jackson should be enough, but, on the other hand, it's worth knowing what are some of the most popular JSON parsing library exists in your disposal. 

In this article, I am going to share 5 useful JSON libraries that I believe every Java JEE developer should be aware of.

If you are new to JSON, probably heard about it but don't know what is JSON there here is a brief introduction of JSON for you. The JSON is an acronym for JavaScript Object Notation, is a lightweight data-interchange format, an alternative to XML, but smaller, faster, and easier to parse.

Because JSON uses the JavaScript syntax for describing data objects, it is language and platform-independent and many parsers and libraries have been developed over the years. You can also read Java XML and JSON to learn more about the pros and cons of JSON over XML.

And, if you are new to JSON Parsing in Java then I highly recommend you check out Jackson library. It's a very useful, versatile, and high-performance library for parsing JSON and CSV files and I think every Java developer should know about it. If you need a resource, check out this Jackson Quick Start: JSON Serialization With Java Made Easy - a free course on Udemy to learn Jackson API basics.

5 Useful JSON libraries in Java

Here is my list of the most useful and essential JSON libraries for Java developers. Though I have used them some or other time or other I mostly prefer Jackson because it's feature-rich and I believe inconsistency. 

It doesn't mean those other libraries are not useful, they also have their own strength like Gson is much simpler to use as compared to Jackson and json-simple is a really light-weight library without any third-party dependency.

As the purpose of this article is to make you, a Java developer aware of useful JSON library, I leave the decision of choosing the JSON library for yourself. Depending upon your need, you can choose any of them.

1. Jackson

Jackson is a multi-purpose Java library for processing JSON data format. Jackson aims to be the best possible combination of fast, correct, lightweight, and ergonomic for developers.

Jackson offers three methods for processing JSON format, each of them having its pros and cons:

1. Streaming API or incremental parsing/generation: reads and writes JSON content as discrete events
2. Tree model: provides a mutable in-memory tree representation of a JSON document
3. Data binding: converts JSON to and from POJO’s

If you are only interested in converting Java objects to and from JSON string then the third method is most appropriate for you.

The pros of Jackson are that It provides heaps of features and looks to be a good tool for reading and writing JSON in a variety of ways, but at the same time, its size becomes a disadvantage if your requirement is just to serialize and deserialize Java object to JSON String. Y

In order to use Jackson, you can include the following maven dependency or manually include jackson-core-2.3.1.jar, jackson-databind-2.3.1.jar, and jackson-annotations-2.3.1.jar in Classpath.

If you are serious about learning REST API then you can also check out Master Java Web Services and REST API with Spring Boot course on Udemy. It's a great course to start with Java web services, particularly REST API with Spring Boot. 

best JSON libraries in Java


The second Java JSON binding library we will discuss is Gson, or if you prefer the full name, the google-gson library. Gson is a Java library capable of converting Java Objects into their JSON representation and JSON strings to an equivalent Java object without the need for placing Java annotations in your classes.

Some of the salient features of the Gson library are:
  • Provides simple toJson() and fromJson methods to convert Java objects to JSON and vice-versa
  • Supports arbitrarily complex objects
  • It has extensive support of Java Generics
  • Allow custom representation for objects
  • Allow pre-existing unmodifiable objects to be converted to and from JSON
Both Gson and Jackson are powerful and extremely popular and now it's up to you to decide which one to use in your project. This is part of the software design process where you need to choose a framework and libraries for your application. If you are new to this process, I recommend joining the Software Architecture in Java: Design & Development course on Educative, a text-based interactive learning platform.

best software architecture course for java developers

3. json-simple 

The json-simple is one of the simplest JSON library, also lightweight. You can use this library to encode or decode JSON text. It's an open-source lightweight library that is flexible and easy to be used by reusing Map and List interfaces from JDK. A good thing about this library that it has no external dependency and both source and binary are JDK 1.2 compatible.

Pros of Json-simple is that it is lightweight, just 12 classes and it provides support for Java IO readers and writers. You can take your decision better if you know about JSON format, like,  how information is represented there. I would suggest reading Beginning JSON by Ben Smit to learn more about JSON format.

If you are looking for a simple lightweight Java library that reads and writes JSON and supports Streams, json-simple is probably a good match. It does what it says with just 12 classes, and works on legacy (1.4) JREs as well.

In order to use JSON-Simple API, you need to include maven dependency in your project's pom.xml file or alternatively, you can also include the following JAR files in your classpath. You can also see this tutorial to learn about how to read JSON String in Java using json-simple.

JSON - Jackson vs Gson

4. Flexjson

Flexjson is another lightweight library for serializing and deserializing Java objects into and from JSON format allowing both deep and shallow copies of objects. 

The depth to which an object is serialized can be controlled with Flexjson and thus making it similar to lazy-loading, allowing us to extract only the information we need. This is not the case since we want an entire object to be written to file, but it’s good to know that it can do that.

If you know that you are going to use only a small amount of data in your application and you wish to store or read it to and from JSON format, you should consider using Flexjson or Gson. You can also see this tutorial to convert JSON String to Java object using Jackson.

5. JSON-lib

JSON-lib is a Java library, based on the work by Douglas Crockford, capable of transforming beans, maps, collections, java arrays, and XML to JSON and back again to beans and DynaBeans.

If you are going to use large amounts of data and wish to store or read it to and from JSON format, you should consider using Jackson or JSON-lib.

You can read more about how to parse JSON String in Java using these libraries on Developing RESTful Services with JAX-RS 2.0, WebSockets, and JSON, one of the better book which explains how to use consume JSON data from web services.

Top 5 JSON Library Java JEE Developers Should Know

That's all about some of the useful JSON libraries in Java. You can use these libraries to parse JSON String and generate Java objects or create JSON String from your existing Java objects. If you are dealing with Web services that return JSON response then these libraries are very important for you.

You can choose between them depending upon your need like if you need features and speed then Jackson is probably the best, if you need simplicity then Google Gson looks better to me and if you are concerned about third-party dependencies then json-simple or Flexjson can be a good choice.

Further Learning
Java Web Fundamentals
Master Java Web Services and REST API with Spring Boot
Software Architecture in Java: Design & Development

Other Java and JSON articles for Java Programmers
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  • How to parse JSON to/from Java Object using Jackson? (tutorial)
  • The Complete Professional Java Developer RoadMap (guide)
  • How to use Google Protocol Buffer (protobuf) in Java? (tutorial)
  • Top 10 RESTful Web Service Interview Questions (see here)
  • 10 Best Spring Framework Courses for Beginners (online courses)
  • How to convert a JSON  String to POJO in Java? (tutorial)
  • 3 Ways to parse JSON String in Java? (tutorial)
  • How to convert JSON array to String array in Java using Gson? (tutorial)
  • My Favorite Courses to learn Software Architecture (courses)
  • How to parse a large JSON file using Jackson Streaming API? (example)
  • What is the purpose of different HTTP methods in REST? (see here)
  • 10 Advanced Spring Boot Courses for Java developers (courses)

P. S. - If you want to learn how to develop RESTful Web Services using Spring Framework, check out Eugen Paraschiv's REST with Spring course. He has recently launched the certification version of the course, which is full of exercises and examples to further cement the real world concepts you will learn from the course.

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