How To Convert Json String To Coffee Object - Gson/Json Deserialization Example

In the last article, yous conduct maintain learned how to convert a Java object to JSON String too inward today's article, yous volition acquire the opposite, i.e. converting a JSON String to Java object. The outset instance was known equally JSON serialization instance too this i is known equally JSON deserialization because nosotros are creating a Java object from a String. The thought is really similar to classical Serialization inward Java where yous convert a Java object to some other binary format which tin live transported over the network or tin live saved inward the disk for farther usage. That's why the procedure of converting a Java object to JSON is known equally serialization too converting a JSON document to Java object is known equally De-Serialization. You tin utilization whatever JSON library to perform serialization too de-serialization e.g. Jackson Databind, Gson, or Json-simple.  In this program, I'll demo yous how to utilization Gson to create a Java object from given JSON String.

In fellowship to start with, nosotros demand a JSON String. In the real world, yous tin have JSON String from many different sources e.g. database, from a RESTful Web Services or whatever upstream but hither nosotros tin utilization the i nosotros conduct maintain created inward the concluding article:

{ "name": "John", "email": "john.doe@gmail.com", "age": 29, "phone" : 5168161922, "city" : "NewYork", "hasCreditCard": imitation }

While using JSON String inward Java code, in that location is a littlie problem. Since JSON String are enclosed amongst double quotes, they demand to live escaped inward Java code e.g. every double quotes i.e. " needs to write equally \". This tin live a large occupation if your JSON String is to a greater extent than than a brace of values, thankfully in that location are a brace of ways to solve this problem.



1) Using Eclipse to escape String automatically
Eclipse has this characteristic which automatically escapes whatever grapheme within String literal when yous glue a String inward code. Which agency double quotes to a greater extent than or less JSON keys tin automatically live replaced whenever yous enable this setting inward Eclipse equally shown below:

You tin encounter this tutorial to acquire to a greater extent than virtually how to enable escape String setting inward Eclipse too how to automatically escape JSON String inward Java.




2) Use Single Quotes
Even though JSON touchstone defines that JSON properties should live wrapped inward quotation grade or double quotes " ", yous tin utilization unmarried quotes to avoid tons of \" Java escaping inward your String. Thankfully, Gson accepts keys inward both unmarried quotes too double quotes e.g. yous tin write either "name" or 'name', both are valid. Using unmarried quotes or apostrophes volition brand your code to a greater extent than readable, equally shown below:

String json = "{ 'name':'John',  'email':'john.doe@gmail.com',  'age':29,  'phone':5168161922,  'city':'NewYork',  'hasCreditCard':false  }";

You tin encounter hither nosotros don't demand to escape whatever String within JSON, which makes it to a greater extent than readable.

Steps to convert a JSON String to Java Object (De-Serialization)

Here are the basic steps to convert a JSON String to Java using Google's Gson library. Basically, yous hand a JSON document to Gson too it volition render a Java object, whose plain is populated using values given inward JSON String. Since Gson doesn't know which course of pedagogy of object given JSON needs to live converted, yous besides demand to say him the course of pedagogy name.

1) Download Gson library too add together JAR into the classpath, if yous are using Maven merely add together the dependency inward your pom.xml file.

2) Create the String yous desire to convert into a Java object.

3) Create the object of Gson class, a helper course of pedagogy to convert a JSON String to a coffee object.

4) Call the Gson.fromJSon(json, UserDetails.class) to convert the given JSON String to object of the course of pedagogy given equally the minute argument. This method returns a Java object whose fields are populated using values given inward JSON String.

Java Program to convert JSON String to Java Object

import com.google.gson.Gson;  /**  * Java Program to convert JSON String to Java Object using Gson.   *   * @author WINDOWS 8  *  */ public class App {    public static void main(String args[]) {      String json = "{ 'name':'John', 'email':'john.doe@gmail.com',      'age':29, 'phone':5168161922, 'city':'NewYork', 'hasCreditCard':false }";          Gson gson = new Gson();          UserDetails user = gson.fromJson(json, UserDetails.class);          System.out.println(user);        }  }  class UserDetails {    private String name;   private String email;   private int age;   private long phone;   private String city;   private boolean hasCreditCard;  }

You tin encounter how nosotros conduct maintain to overstep the course of pedagogy of the expected Java object equally the minute parameter. Otherwise, Gson doesn't know which object it needs to map given JSON String.

When yous impress the user object yous tin encounter that it contains the values from the provided JSON String. You tin besides encounter those values inward the debugger if yous are using Eclipse for debugging equally shown inward the next screenshot.

How to compile too run this program?

Similar to the concluding example, if yous are using Maven too thus yous tin utilization next dependency to download Gson.jar file automatically. Alternatively, yous tin manually download Gson.jar from Maven Central library too pose it on your application's classpath.

maven dependency

<dependency>   <groupId>com.google.code.gson</groupId>   <artifactId>gson</artifactId>   <version>2.3.1</version> </dependency>

If yous conduct maintain problem running a programme inward Eclipse, encounter here, or, if yous are running the programme from the ascendance business too thus yous tin follow steps given hither to add together whatever external JAR to the classpath.


That's all virtually how to convert a JSON String to Java object using Gson library. It is really simple, yous merely demand to utilization the fromJson() method of Gson course of pedagogy too yous are done. This is the simplest way to convert a JSON String inward Java, I don't scream upward it tin acquire whatever simpler than this. You merely demand to include the Gson.jar file inward your application's classpath or fifty-fifty meliorate merely utilization Maven or Gradle to contend dependencies too acquire rid of manual downloading JAR too adding into classpath stuff.

Further Learning
Master Java Web Services too REST API amongst Spring Boot
REST API Design, Development & Management
answer)

Top 10 RESTful Web Service Interview Questions (see here)

How to utilization Google Protocol Buffer inward Java? (tutorial)

How to parse large JSON file using Jackson Streaming API? (example)

5 Books to Learn REST too RESTful Web Services (books)

What is the role of dissimilar HTTP methods inward REST? (see here)

How to eat JSON from RESTful Web Services using RestTemplate of Spring? (tutorial)

How to convert JSON to HashMap too vice-versa (tutorial)

Thanks for reading this article. If yous similar this article too thus delight part amongst your friends too colleagues, if yous conduct maintain whatever questions or feedback too thus delight driblet a comment.

P.S. - If yous desire to acquire to a greater extent than virtually the advanced theme inward Java, I besides advise yous reading "Core Java Volume 2 - Advanced Features" By Cay S. Horstmann, it covers several advanced Java features e.g. JAXB, JDBC etc.