Simple JSON Serializer (from Object to JSON).

JsonSerializer.java

package ge.tsu.serializer.json;

import java.lang.reflect.Field;
import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.Temporal;

public class JsonSerializer {

	public static void main(String... args) throws Exception {
		
		Author[] authors = { 
				new Author("Hiroshi", "Sakurazaka", LocalDate.of(1970, 1, 1), false),
				new Author("Vakhtangi", "Laluashvili", LocalDate.of(1993, Month.MAY, 14), false), 
		};
		Book book = new Book("All You Need is Kill", authors, 2004);

		String json = toJson(book, Book.class);
		System.out.println(json);
	}

	public static String toJson(Object obj, Class<?> clazz) throws Exception {

		StringBuilder sb = new StringBuilder();

		if (clazz.isArray()) {

			sb.append("[");
			
			Object[] objects = (Object[]) obj;
			
			int idx = 0;
			for (Object o : objects) {
				sb.append(toJson(o, o.getClass()));
				if (idx < objects.length - 1) {
					sb.append(",");
				}
				++idx;
			}
			
			sb.append("]");

		} else {

			sb.append("{");

			Field[] fields = clazz.getDeclaredFields(); // get all fields for current class
			int idx = 0;
			for (Field field : fields) {
				
				// Serialize name
				String name = field.getName();
				sb.append("\"").append(name).append("\":");
				
				// Serialize value
				Object value = field.get(obj);

				// Serialize sub-objects 
				// but not 'Strings', 'primitive', or 'date types'!
				if (Object.class.isInstance(value) 
						&& !String.class.isInstance(value)
						&& !Temporal.class.isInstance(value)
						&& !field.getType().isPrimitive()) {
					sb.append(
							toJson(value, field.getType())
					);
				} else {
					// wrap value in quotes if not a JSON object or array
					sb.append("\"").append(value).append("\"");
				}
				
				if (idx < fields.length - 1) {
					sb.append(",");
				}
				++idx;
			}

			sb.append("}");
		}
		return sb.toString();
	}
}