如何通过freemarker中的键值访问json值？

{
  "name": "John",
  "age": 25,
  "email": "john@example.com"
}

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;
import freemarker.template.TemplateExceptionHandler;

import java.io.IOException;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

public class FreemarkerExample {
    public static void main(String[] args) {
        Configuration cfg = new Configuration(Configuration.VERSION_2_3_31);
        cfg.setClassForTemplateLoading(FreemarkerExample.class, "/templates");
        cfg.setDefaultEncoding("UTF-8");
        cfg.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);

        try {
            Template template = cfg.getTemplate("example.ftl");

            Map<String, Object> data = new HashMap<>();
            data.put("name", "John");
            data.put("age", 25);
            data.put("email", "john@example.com");

            StringWriter writer = new StringWriter();
            template.process(data, writer);

            System.out.println(writer.toString());
        } catch (IOException | TemplateException e) {
            e.printStackTrace();
        }
    }
}