Example on using Jankson for reading and writing to a file.

JanksonExample.java

//usr/bin/env jbang "$0" "$@";exit $?
//DEPS blue.endless:jankson:1.2.1

import java.io.IOException;
import java.io.Writer;
import java.io.BufferedInputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.charset.Charset;
import static java.nio.file.StandardOpenOption.CREATE;
import static java.nio.file.StandardOpenOption.WRITE;

import blue.endless.jankson.Jankson;
import blue.endless.jankson.Comment;
import blue.endless.jankson.JsonGrammar;
import blue.endless.jankson.JsonElement;
import blue.endless.jankson.JsonObject;

class ConfigObject {
  transient int bar = 8192; //transient fields are not serialized
  public static String bux = "a"; //static fields are not serialized

  //the Comment annotation is picked up by jankson.Comment and added to the json in toJson()
  @Comment("This is a comment")
  private int foo = 42; //private fields ARE serialized.
  private String word = "example";
  private float value = 0.125f;
  private boolean useSomething = true;
}

public class JanksonExample {
  public static Charset charset = java.nio.charset.StandardCharsets.UTF_8;
  public static final JsonGrammar HJSON = JsonGrammar.builder()
    .withComments(true)
    .printCommas(false)
    .bareSpecialNumerics(true)
    .printUnquotedKeys(true)
    .build();
  public static void main(String[] args) throws IOException {
    Path dir = Paths.get("testdir");
    Path filePath = dir.resolve(Paths.get("config.hjson")).normalize();
    if(!Files.exists(dir)) {
      Files.createDirectories(dir);
    }
    Jankson jankson = Jankson.builder().build();
    if(!Files.exists(filePath) || Files.size(filePath) == 0) {
      JsonElement element = jankson.toJson(new ConfigObject());
      try(Writer writer = Files.newBufferedWriter(filePath, charset, CREATE, WRITE)) {
        element.toJson(writer, HJSON, 0);
        writer.flush(); writer.close();
      } catch(Exception e) {
        e.getStackTrace();
      }
    }
    try(BufferedInputStream bis = new BufferedInputStream(Files.newInputStream(filePath))) {
      JsonObject hjson = jankson.load(bis);
      int numRes = hjson.getInt("foo", 1);
      String wordRes = hjson.get(String.class, "word");
      float flRes = hjson.getFloat("value", 0.5f);
      boolean boolRes = hjson.getBoolean("useSomething", false);
      String confRes = ConfigObject.bux;
      System.out.println(numRes);
      System.out.println(wordRes);
      System.out.println(flRes);
      System.out.println(boolRes);
      System.out.println(confRes);
      bis.close();
    } catch(Exception e) {
      e.getStackTrace();
    }
  }
}