How to convert JSON String to Java Object - Gson/JSON Deserialization Example

In the last article, y'all have got learned how to convert a Java object to JSON String too inward today's article, y'all volition acquire the opposite, i.e. converting a JSON String to Java object. The outset instance was known equally JSON serialization instance too this ane 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 y'all 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 whatsoever JSON library to perform serialization too de-serialization e.g. Jackson Databind, Gson, or Json-simple. In this program, I'll demo y'all how to utilization Gson to create a Java object from given JSON String.

In fellowship to start with, nosotros involve a JSON String. In the real world, y'all tin have JSON String from many different sources e.g. database, from a RESTful Web Services or whatsoever upstream but hither nosotros tin utilization the ane nosotros have got created inward the terminal article:

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

While using JSON String inward Java code, in that location is a littlie problem. Since JSON String are enclosed amongst double quotes, they involve 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 dyad of values, thankfully in that location are a dyad of ways to solve this problem.

1) Using Eclipse to escape String automatically
Eclipse has this characteristic which automatically escapes whatsoever grapheme within String literal when y'all glue a String inward code. Which way double quotes only about JSON keys tin automatically live replaced whenever y'all enable this setting inward Eclipse equally shown below:

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

2) Use Single Quotes
Even though JSON measure defines that JSON properties should live wrapped inward quotation grade or double quotes " ", y'all 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. y'all 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 meet hither nosotros don't involve to escape whatsoever 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, y'all hand a JSON document to Gson too it volition render a Java object, whose champaign is populated using values given inward JSON String. Since Gson doesn't know which degree of object given JSON needs to live converted, y'all too involve to say him the degree name.

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

2) Create the String y'all desire to convert into a Java object.

3) Create the object of Gson class, a helper degree 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 degree given equally the minute argument. This method returns a Java object whose fields are populated using values given inward JSON String.

how to convert a Java object to JSON String How to convert JSON String to Java Object - Gson/JSON Deserialization Example

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 meet how nosotros have got to exceed the degree of the expected Java object equally the minute parameter. Otherwise, Gson doesn't know which object it needs to map given JSON String.

When y'all impress the user object y'all tin meet that it contains the values from the provided JSON String. You tin too meet those values inward the debugger if y'all are using Eclipse for debugging equally shown inward the next screenshot.

How to compile too run this program?

Similar to the terminal example, if y'all are using Maven hence y'all tin utilization next dependency to download Gson.jar file automatically. Alternatively, y'all tin manually download Gson.jar from Maven Central library too position 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 y'all have got problem running a programme inward Eclipse, meet here, or, if y'all are running the programme from the ascendency occupation hence y'all tin follow steps given hither to add together whatsoever external JAR to the classpath.

That's all most how to convert a JSON String to Java object using Gson library. It is really simple, y'all only involve to utilization the fromJson() method of Gson degree too y'all are done. This is the simplest way to convert a JSON String inward Java, I don't cry upwards it tin acquire whatsoever simpler than this. You only involve to include the Gson.jar file inward your application's classpath or fifty-fifty ameliorate only utilization Maven or Gradle to cope dependencies too acquire rid of manual downloading JAR too adding into classpath stuff.

Other Java JSON tutorials y'all may like

How to convert JSON array to String array inward Java? (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 unlike HTTP methods inward REST? (see here)
How to swallow 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 y'all similar this article hence delight portion amongst your friends too colleagues, if y'all have got whatsoever questions or feedback hence delight drib a comment.

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