What is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It's easy for humans to read and write, and easy for machines to parse and generate. JSON is language-independent and uses conventions familiar to programmers of the C-family of languages.

JSON Structure and Types

JSON is built on two structures:

• A collection of name/value pairs (realized as an object, record, struct, dictionary, hash table, keyed list, or associative array)
• An ordered list of values (realized as an array, vector, list, or sequence)

JSON has the following data types:

• Number: A signed decimal number
• String: A sequence of zero or more Unicode characters
• Boolean: true or false
• Array: An ordered list of zero or more values
• Object: An unordered collection of key-value pairs
• null: An empty value

JSON Examples

Simple JSON Object

{
  "name": "John Doe",
  "age": 30,
  "city": "New York"
}

JSON Array

[
  "apple",
  "banana",
  "cherry"
]

Nested JSON Object

{
  "person": {
    "name": "Jane Smith",
    "age": 28,
    "address": {
      "street": "123 Main St",
      "city": "Boston",
      "country": "USA"
    },
    "hobbies": ["reading", "swimming", "photography"]
  }
}

Converting JSON to Java Class

To convert JSON to a Java class, you can use libraries like Gson or Jackson. Here's an example using Jackson:

import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonToJavaExample {
    public static void main(String[] args) throws Exception {
        String json = "{"name":"John Doe","age":30,"city":"New York"}";
        
        ObjectMapper objectMapper = new ObjectMapper();
        Person person = objectMapper.readValue(json, Person.class);
        
        System.out.println(person.getName());
        System.out.println(person.getAge());
        System.out.println(person.getCity());
    }
}

class Person {
    private String name;
    private int age;
    private String city;

    // Getters and setters
}

Useful Tools for Working with JSON

• Postman: A popular API development and testing tool that supports JSON formatting and validation.
• IntelliJ IDEA: An IDE with excellent JSON support, including syntax highlighting, validation, and schema support.
• JetBrains Fleet: A lightweight, polyglot IDE that provides JSON support among many other languages.

Top 10 Common JSON Errors and How to Fix Them

1. Missing or extra comma: Ensure all elements in objects and arrays are separated by commas, but don't add a comma after the last element.
2. Unquoted keys: All keys in JSON objects must be enclosed in double quotes.
3. Single quotes instead of double quotes: JSON requires double quotes for strings and keys.
4. Trailing comma in arrays or objects: Remove any comma that appears after the last element in an array or object.
5. Incorrect boolean values: Use lowercase `true` and `false` for boolean values.
6. Unescaped characters in strings: Escape special characters like quotes and backslashes with a backslash.
7. Invalid number formats: Ensure numbers are correctly formatted (e.g., no leading zeros for integers).
8. Mismatched brackets or braces: Check that all opening brackets and braces have matching closing ones.
9. Using comments: JSON doesn't support comments. Remove any comments from your JSON data.
10. Mixing arrays and objects: Ensure you're using the correct data structure (array `[]` or object ``) for your data.