About the Tutorial

Google Gson

About the Tutorial

Google Gson is an open source, Java-based library developed by Google. It facilitates serialization of Java objects to JSON and vice versa. This tutorial adopts a simple and intuitive way to describe the basic-to-advanced concepts of Google Gson and how to use its APIs.

Audience

This tutorial will be useful for most Java developers, starting form beginners to experts. After completing this tutorial, we are confident that you will find it easy to use Google Gson in your programs.

Prerequisites

It is a simple tutorial that any developer with a little exposure to Java programming can easily understand.

Copyright & Disclaimer

Copyright 2016 by Tutorials Point (I) Pvt. Ltd. All the content and graphics published in this e-book are the property of Tutorials Point (I) Pvt. Ltd. The user of this e-book is prohibited to reuse, retain, copy, distribute or republish any contents or a part of contents of this e-book in any manner without written consent of the publisher. We strive to update the contents of our website and tutorials as timely and as precisely as possible, however, the contents may contain inaccuracies or errors. Tutorials Point (I) Pvt. Ltd. provides no guarantee regarding the accuracy, timeliness or completeness of our website or its contents including this tutorial. If you discover any errors on our website or in this tutorial, please notify us at contact@

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Google Gson

Table of Contents

About the Tutorial ............................................................................................................................................ i Audience........................................................................................................................................................... i Prerequisites..................................................................................................................................................... i Copyright & Disclaimer ..................................................................................................................................... i Table of Contents ............................................................................................................................................ ii

1. Gson Overview.......................................................................................................................................1 Features of Gson ............................................................................................................................................. 1 Three Ways of Processing JSON ...................................................................................................................... 2

2. Gson Environment Setup........................................................................................................................3 Local Environment Setup................................................................................................................................. 3 Popular Java Editors ........................................................................................................................................ 4 Download Gson Archive .................................................................................................................................. 4 Set Gson Environment ..................................................................................................................................... 4 Set CLASSPATH variable................................................................................................................................... 5

3. Gson First Application ............................................................................................................................6 Example ........................................................................................................................................................... 6 Steps to Remember ......................................................................................................................................... 7

4. Gson Gson Class .....................................................................................................................................9 Class Declaration ............................................................................................................................................. 9 Constructors .................................................................................................................................................... 9 Class Methods ................................................................................................................................................. 9 Methods inherited......................................................................................................................................... 11 Example ......................................................................................................................................................... 11

5. Gson Object Serialization .....................................................................................................................13 Example ......................................................................................................................................................... 13

6. Gson Data Binding................................................................................................................................16 Primitives Data Binding ................................................................................................................................. 16 Example ......................................................................................................................................................... 16

7. Gson Object Data Binding ....................................................................................................................18 Example ......................................................................................................................................................... 18

8. Gson Tree Model..................................................................................................................................20 Create Tree from JSON .................................................................................................................................. 20 Traversing Tree Model................................................................................................................................... 20 Example ......................................................................................................................................................... 20

9. Gson ? Streaming....................................................................................................................................23 Example ......................................................................................................................................................... 23

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Google Gson 10. Gson Serialization Examples.................................................................................................................27

Array Example ............................................................................................................................................... 27 Collections Example....................................................................................................................................... 28 Generics Example .......................................................................................................................................... 30 11. Gson Serializing Inner Classes...............................................................................................................34 Nested Inner Class example .......................................................................................................................... 34 Nested Static Inner Class Example................................................................................................................. 36 12. Gson Custom Type Adapters ................................................................................................................40 Create a Custom Adapter .............................................................................................................................. 40 Register the Custom Adapter ........................................................................................................................ 40 Use the Adapter ............................................................................................................................................ 40 Example ......................................................................................................................................................... 41 13. Gson Null Object Support.....................................................................................................................44 Example without serializeNulls Call ............................................................................................................... 44 Example with serializeNulls call..................................................................................................................... 46 14. Gson Versioning Support......................................................................................................................48 Example ......................................................................................................................................................... 48 15. Gson Excluding Fields from Serialization ..............................................................................................51 Example ......................................................................................................................................................... 51 Using excludeFieldsWithModifiers ................................................................................................................ 53 Using @Expose Annotation ........................................................................................................................... 55

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1. GSON OVERVIEW

Google Gson

Google Gson is a simple Java-based library to serialize Java objects to JSON and vice versa. It is an open-source library developed by Google. The following points highlight why you should be using this library:

Standardized - Gson is a standardized library that is managed by Google. Efficient - It is a reliable, fast, and efficient extension to the Java standard library. Optimized - The library is highly optimized. Support Generics - It provides extensive support for generics. Supports complex inner classes - It supports complex objects with deep

inheritance hierarchies.

Features of Gson

Here is a list of some of the most prominent features of Gson: Easy to use Gson API provides a high-level facade to simplify commonly used usecases. No need to create mapping Gson API provides default mapping for most of the objects to be serialized. Performance Gson is quite fast and is of low memory footprint. It is suitable for large object graphs or systems. Clean JSON Gson creates a clean and compact JSON result which is easy to read. No Dependency Gson library does not require any other library apart from JDK. Open Source Gson library is open source; it is freely available.

Three Ways of Processing JSON

Gson provides three alternative ways to process JSON:

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