How to parse JSON in Java

JSON (JavaScript Object Notation) is a lightweight, text-based, language-independent data exchange format. It is easy to read, write, and parse, making it widely used for data transfer between applications. JSON supports two main structured types:

• Object: An unordered collection of name/value pairs
• Array: An ordered list of values

Values can be strings, numbers, booleans, null, objects, or arrays.

Sample JSON Structure.

{
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address": {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": 10021
},
"phoneNumbers": [
{ "type": "home", "number": "212 555-1234" },
{ "type": "fax", "number": "646 555-4567" }
]
}

JSON Processing in Java

Java does not have built-in JSON parsing support before Java 9, so external libraries are commonly used. In this article, we use JSON.simple, a lightweight and easy-to-use library.

JSON.simple Features:

• Parse JSON from strings or files.
• Create JSON objects and arrays.
• Simple API (JSONObject, JSONArray).
• Minimal dependencies.

Dependency Setup

Maven Dependency:

<dependency>
<groupId>com.googlecode.json-simple</groupId>
<artifactId>json-simple</artifactId>
<version>1.1.1</version>
</dependency>

Core JSON.simple Classes

Write JSON to a file

This example creates a JSON object and writes it to a file using JSONObject and JSONArray.

Output (JSONExample.json)

Note : JSON objects are unordered by definition, so key order is not guaranteed.

Read JSON from a file

This example reads and parses the previously created JSON file.

Output: