JSON Data Serialization & Engine Parsing Mechanics

// -------------------------------------------------------------
// 1. VALID JSON (Adheres strictly to RFC 8259)
// -------------------------------------------------------------
{
  "employeeId": 1088,
  "fullName": "Alex Mercer",
  "isRemote": true,
  "roles": ["Admin", "Architect"],
  "metadata": null,
  "score": 98.6
}

// -------------------------------------------------------------
// 2. INVALID JSON (Triggers Lexical Parsing Exception)
// -------------------------------------------------------------
{
  'employeeId': 1088,           // ERROR 1: Single quotes used for key!
  fullName: "Alex Mercer",      // ERROR 2: Unquoted key!
  "isRemote": True,             // ERROR 3: Capitalized "True"!
  "roles": ["Admin", "Architect",], // ERROR 4: Trailing comma after item!
  "status": undefined,          // ERROR 5: "undefined" is invalid!
  "score": NaN,                 // ERROR 6: "NaN" is invalid!
  // This is a comment          // ERROR 7: Comments are strictly FORBIDDEN!
}

Stream Byte Payload (100 MB JSON File)
   │
   ├──────> AST Tree Parsing (JSONObject / ObjectMapper.readTree())
   │        Loads all 100 MB into memory as nested Java Objects.
   │        Total Heap Memory: ~350 MB to 500 MB (Risk of OutOfMemoryError).
   │
   └──────> Streaming Tokenizer Parsing (Jackson JsonParser)
            Reads token-by-token (START_OBJECT -> FIELD_NAME -> VALUE_STRING).
            Total Heap Memory: ~8 KB (Constant Memory footprint).

import org.json.JSONArray;
import org.json.JSONObject;

public class JSONOrgDemo {
    public static void main(String[] args) {
        String jsonText = "{"
                + "\"company\": \"TechCorp\","
                + "\"employees\": ["
                + "  {\"id\": 101, \"name\": \"Darshan\", \"salary\": 85000},"
                + "  {\"id\": 102, \"name\": \"Priya\"}"
                + "]"
                + "}";

        JSONObject root = new JSONObject(jsonText);
        String companyName = root.getString("company");

        JSONArray employees = root.getJSONArray("employees");
        for (int i = 0; i < employees.length(); i++) {
            JSONObject emp = employees.getJSONObject(i);
            String name = emp.getString("name");
            
            // USE optDouble / optInt TO AVOID JSONException ON MISSING KEYS!
            double salary = emp.optDouble("salary", 50000.0);
            
            System.out.println("Employee: " + name + " | Salary: $" + salary);
        }
    }
}

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.databind.ObjectMapper;

@JsonIgnoreProperties(ignoreUnknown = true)
class Employee {
    private int id;
    private String name;

    public Employee() {}

    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

public class JacksonDemo {
    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        String jsonInput = "{\"id\": 101, \"name\": \"Darshan\", \"extra_field\": \"ignored\"}";

        // Deserialization: JSON -> Java POJO Instance
        Employee emp = mapper.readValue(jsonInput, Employee.class);
        System.out.println("Parsed Employee Name: " + emp.getName());

        // Serialization: Java POJO -> JSON String
        String jsonOutput = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(emp);
        System.out.println("Serialized JSON:\n" + jsonOutput);
    }
}