Java: JSON Library

Below is a list of major JSON format processing libraries for java. Check it out.

• JSON Processing
• Summary
• JSR 353: Java API for JSON Processing - Reference Implementation
• Comment
• the java version official implementation
• JSON in Java (json.org)
• Summary
• json.org official implementation
• Comment
• The API requires you to load the entire document into a String. This is somewhat cumbersome to use and inefficient for large documents. But it's a DOM model so you can get a lot done with very little code. 
• Jackson JSON Processor
• Summary
• High-performance JSON processor.
• Comment
• Jackson ones to be the fastest json processing library in the old age.
• Has many features with modules approach.
• Jackson has grown into a huge collection of data type processing library
• Boon JSON
• Summary
• Boon is a opinionated, low ceremony Java framework -- from Birth of Boon
• An utility library to simplify java development
• Comment
• Claim to be the fastest JSON Library, see:
• Boon JSON in five minutes, Faster Java JSON parsing, and serialization! 
• Java JSON Benchmark 
• The JSON parser which has now been ported / forked into Groovy 2.3.  
• Built-in path expressions, see Boon path expressions

• google-gson 
• Summary
• A Java library to convert JSON to Java objects and vice-versa
• Feature
• Provide simple toJson() and fromJson() methods to convert Java objects to JSON and vice-versa
• Allow pre-existing unmodifiable objects to be converted to and from JSON
• Extensive support of Java Generics
• Allow custom representations for objects
• Support arbitrarily complex objects (with deep inheritance hierarchies and extensive use of generic types)

• json-simple
• Summary
• JSON.simple is a simple Java toolkit for JSON. You can use JSON.simple to encode or decode JSON text. 
• Feature
• Full compliance with JSON specification (RFC4627) and reliable (see compliance testing)
• Provides multiple functionalities such as encode, decode/parse and escape JSON text while keeping the library lightweight
• Flexible, simple and easy to use by reusing Map and List interfaces
• Supports streaming output of JSON text
• Stoppable SAX-like interface for streaming input of JSON text (learn more)
• Heap based parser
• High performance (see performance testing)
• No dependency on external libraries
• Both of the source code and the binary are JDK1.2 compatible
• Comment
• Can use with JXPath (see below). see JSON XPath and Java
• genson - A fast & extensible Java <> Json library
• Summary
• Genson is an open-source library doing conversion from Java to Json and Json to Java. Genson targets people who want an extensible but also configurable, fast, scalable and easy to use library. 
• Feature
• Easy to use, fast, highly configurable, lightweight and all that into a single small jar!
• Full databinding and streaming support for efficient read/write
• Support for polymorphic types (able to deserialize to an unknown type)
• Does not require a default no arg constructor and really passes the values not just null, encouraging immutability. It can even be used with factory methods instead of constructors!
• Full support for generic types
• Easy to filter/include properties without requiring the use of annotations or mixins
• You can apply filtering or transformation logic at runtime on any bean using the BeaView mechanism
• Genson provides a complete implementation of JSR 353
• Starting with Genson 0.95 JAXB annotations and types are supported!
• Automatic support for JSON in JAX-RS implementations
• Serialization and Deserialization of maps with complex keys
•  Comment
• Looks good!

 Want to use XPath with JSON? see below.

• Commons JXPath
• Summary
• The org.apache.commons.jxpath package defines a simple interpreter of an expression language called XPath. JXPath applies XPath expressions to graphs of objects of all kinds: JavaBeans, Maps, Servlet contexts, DOM etc, including mixtures thereof.  
• json-path 
• Summary
• Java JsonPath implementation