Convert JSON and YAML in Java (using Jackson and SnakeYAML)

Overview

--Convert JSON and YAML in Java (using Jackson and SnakeYAML) --Jazz to convert JSON to Java object and SnakeYAML to convert Java object to YAML --SnakeYAML to convert YAML to Java objects and Jackson to convert Java objects to JSON --Environment: Java 15 (AdoptOpenJDK 15 + 36) + Jackson Databind 2.11.3 + ShakeYAML 1.27 + Gradle 6.6.1

Build build environment / execution environment with Gradle

Prepare the following build.gradle.

plugins {
  id 'java'
}

repositories {
  mavenCentral()
}

dependencies {
  //Use Jackson Databind
  implementation 'com.fasterxml.jackson.core:jackson-databind:2.11.3'

  //Use ShakeYAML
  implementation 'org.yaml:snakeyaml:1.27'
}

//Define a task that runs the JsonToYaml class
task jsonToYaml(type: JavaExec) {
  main = 'JsonToYaml'
  classpath = sourceSets.main.runtimeClasspath
}

//Define a task that runs the YamlToJson class
task yamlToJson(type: JavaExec) {
  main = 'YamlToJson'
  classpath = sourceSets.main.runtimeClasspath
}

Prepare a class to output the contents of Java object

In order to understand the data structure and class when JSON or YAML is converted to Java object, prepare a class that outputs the object information.

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 *Output the contents of Java objects derived from JSON or YAML.
 */
public class ObjectDumper {

  private static final int INDENT = 2;

  public static String dump(Map<String, Object> obj) {
    List<String> buffer = new ArrayList<String>();
    dumpMap(obj, 0, buffer);
    return String.join("\n", buffer);
  }

  private static void dumpMap(Map<String, Object> obj, int depth, List<String> buffer) {
    for (Map.Entry<String, Object> entry : obj.entrySet()) {
      Object value = entry.getValue();
      if (value instanceof List) {
        buffer.add(line(entry.getKey(), value, depth));
        dumpList((List<Object>) value, depth + 1, buffer);
      } else if (value instanceof Map) {
        buffer.add(line(entry.getKey(), value, depth));
        dumpMap((Map<String, Object>) value, depth + 1, buffer);
      } else {
        buffer.add(line(entry.getKey(), value, depth));
      }
    }
  }

  private static void dumpList(List<Object> array, int depth, List<String> buffer) {
    for (Object element : array) {
      if (element instanceof List) {
        buffer.add(line(element, depth));
        dumpList((List<Object>) element, depth + 1, buffer);
      } else if (element instanceof Map) {
        buffer.add(line(element, depth));
        dumpMap((Map<String, Object>) element, depth + 1, buffer);
      } else {
        buffer.add(line(element, depth));
      }
    }
  }

  private static String line(String key, Object value, int depth) {
    if (value == null) {
      return " ".repeat(INDENT * depth) + key + ": " + "null";
    } else if (value instanceof Map) {
      return " ".repeat(INDENT * depth) + key + ": " + "(" + value.getClass().getName() + ")";
    } else if (value instanceof List) {
      return " ".repeat(INDENT * depth) + key + ": " + "(" + value.getClass().getName() + ")";
    } else {
      return " ".repeat(INDENT * depth) + key + ": " + value.toString() + " (" + value.getClass().getName() + ")";
    }
  }

  private static String line(Object value, int depth) {
    if (value == null) {
      return " ".repeat(INDENT * depth) + "null";
    } else if (value instanceof Map) {
      return " ".repeat(INDENT * depth) + "(" + value.getClass().getName() + ")";
    } else if (value instanceof List) {
      return " ".repeat(INDENT * depth) + "(" + value.getClass().getName() + ")";
    } else {
      return " ".repeat(INDENT * depth) + value.toString() + " (" + value.getClass().getName() + ")";
    }
  }
}

Convert JSON to YAML

Convert with Jackson: JSON → Java object Convert with SnakeYAML: Java Object → YAML

Source code

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.yaml.snakeyaml.DumperOptions;
import org.yaml.snakeyaml.Yaml;

import java.util.Map;

public class JsonToYaml {

  public static void main(String[] args) throws JsonProcessingException {

    //JSON string
    String json = """
      {
        "key": "value",
        "foo": "bar",
        "hoge": "fuga",
        "datalist": [
          {
            "string": "mojiretu",
            "integer": 123456,
            "decimal": 123.456,
            "boolean": true,
            "date": "2020-01-01",
            "timestamp": "2020-01-01T00:00:00.123456789+09:00",
            "nullonly": null,
            "object": {"hoge": "HOGE", "fuga": "FUGA"},
            "array": ["foo", "bar", "baz", ["spam", "ham", "eggs"]]
          },
          {
            "string": "String",
            "integer": 100000,
            "decimal": 999.999,
            "boolean": false,
            "date": "2020-01-01",
            "timestamp": "2020-01-01T00:00:00.123456789+09:00",
            "nullonly": null,
            "object": {"hoge": "Hoge", "fuga": "Fuga"},
            "array": ["Huh", "Bah", "Bazu", ["spam", "Ham", "Egg"]]
          }
        ]
      }
      """;
    System.out.println("**********JSON string to enter**********");
    System.out.println(json);

    System.out.println("**********Convert JSON to Java object**********");
    ObjectMapper mapper = new ObjectMapper();
    Map<String, Object> obj = mapper.readValue(json, new TypeReference<Map<String, Object>>() {
    });
    System.out.println(ObjectDumper.dump(obj));

    System.out.println("**********Convert Java objects to YAML**********");
    DumperOptions opts = new DumperOptions();
    opts.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
    String yaml = new Yaml(opts).dump(obj);
    System.out.println(yaml);
  }
}

Execution result

**********JSON string to enter**********
{
  "key": "value",
  "foo": "bar",
  "hoge": "fuga",
  "datalist": [
    {
      "string": "mojiretu",
      "integer": 123456,
      "decimal": 123.456,
      "boolean": true,
      "date": "2020-01-01",
      "timestamp": "2020-01-01T00:00:00.123456789+09:00",
      "nullonly": null,
      "object": {"hoge": "HOGE", "fuga": "FUGA"},
      "array": ["foo", "bar", "baz", ["spam", "ham", "eggs"]]
    },
    {
      "string": "String",
      "integer": 100000,
      "decimal": 999.999,
      "boolean": false,
      "date": "2020-01-01",
      "timestamp": "2020-01-01T00:00:00.123456789+09:00",
      "nullonly": null,
      "object": {"hoge": "Hoge", "fuga": "Fuga"},
      "array": ["Huh", "Bah", "Bazu", ["spam", "Ham", "Egg"]]
    }
  ]
}

**********Convert JSON to Java object**********
key: value (java.lang.String)
foo: bar (java.lang.String)
hoge: fuga (java.lang.String)
datalist: (java.util.ArrayList)
  (java.util.LinkedHashMap)
    string: mojiretu (java.lang.String)
    integer: 123456 (java.lang.Integer)
    decimal: 123.456 (java.lang.Double)
    boolean: true (java.lang.Boolean)
    date: 2020-01-01 (java.lang.String)
    timestamp: 2020-01-01T00:00:00.123456789+09:00 (java.lang.String)
    nullonly: null
    object: (java.util.LinkedHashMap)
      hoge: HOGE (java.lang.String)
      fuga: FUGA (java.lang.String)
    array: (java.util.ArrayList)
      foo (java.lang.String)
      bar (java.lang.String)
      baz (java.lang.String)
      (java.util.ArrayList)
        spam (java.lang.String)
        ham (java.lang.String)
        eggs (java.lang.String)
  (java.util.LinkedHashMap)
    string:String(java.lang.String)
    integer: 100000 (java.lang.Integer)
    decimal: 999.999 (java.lang.Double)
    boolean: false (java.lang.Boolean)
    date: 2020-01-01 (java.lang.String)
    timestamp: 2020-01-01T00:00:00.123456789+09:00 (java.lang.String)
    nullonly: null
    object: (java.util.LinkedHashMap)
      hoge:Hoge(java.lang.String)
      fuga:Fuga(java.lang.String)
    array: (java.util.ArrayList)
Huh(java.lang.String)
Bah(java.lang.String)
Bazu(java.lang.String)
      (java.util.ArrayList)
spam(java.lang.String)
Ham(java.lang.String)
Egg(java.lang.String)
**********Convert Java objects to YAML**********
key: value
foo: bar
hoge: fuga
datalist:
- string: mojiretu
  integer: 123456
  decimal: 123.456
  boolean: true
  date: '2020-01-01'
  timestamp: '2020-01-01T00:00:00.123456789+09:00'
  nullonly: null
  object:
    hoge: HOGE
    fuga: FUGA
  array:
  - foo
  - bar
  - baz
  - - spam
    - ham
    - eggs
- string:String
  integer: 100000
  decimal: 999.999
  boolean: false
  date: '2020-01-01'
  timestamp: '2020-01-01T00:00:00.123456789+09:00'
  nullonly: null
  object:
    hoge:Hoge
    fuga:Fuga
  array:
  -Huh
  -Bah
  -Bazu
  - -spam
    -Ham
    -Egg

Convert YAML to JSON

Convert with SnakeYAML: YAML → Java object Convert in Jackson: Java Object → JSON

Source code

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.yaml.snakeyaml.Yaml;

import java.util.Map;

public class YamlToJson {

  public static void main(String[] args) throws JsonProcessingException {

    //YAML string
    String yaml = """
      key: value
      foo: bar
      hoge: fuga
      datalist:
      - string: mojiretu
        integer: 123456
        decimal: 123.456
        boolean: true
        date: 2020-01-01
        timestamp: 2020-01-01T00:00:00.123456789+09:00
        nullonly: null
        object:
          hoge: HOGE
          fuga: FUGA
        array:
        - foo
        - bar
        - baz
        - - spam
          - ham
          - eggs
      - string:String
        integer: 100000
        decimal: 999.999
        boolean: false
        date: 2020-01-01
        timestamp: 2020-01-01T00:00:00.123456789+09:00
        nullonly: null
        object:
          hoge:Hoge
          fuga:Fuga
        array:
        -Huh
        -Bah
        -Bazu
        - -spam
          -Ham
          -Egg
      """;
    System.out.println("**********YAML string to enter**********");
    System.out.println(yaml);

    System.out.println("**********Convert YAML to Java object**********");
    Map<String, Object> obj = new Yaml().load(yaml);
    System.out.println(ObjectDumper.dump(obj));

    System.out.println("**********Convert Java objects to JSON**********");
    ObjectMapper mapper = new ObjectMapper();
    String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);
    System.out.println(json);
  }
}

Execution result

**********YAML string to enter**********
key: value
foo: bar
hoge: fuga
datalist:
- string: mojiretu
  integer: 123456
  decimal: 123.456
  boolean: true
  date: 2020-01-01
  timestamp: 2020-01-01T00:00:00.123456789+09:00
  nullonly: null
  object:
    hoge: HOGE
    fuga: FUGA
  array:
  - foo
  - bar
  - baz
  - - spam
    - ham
    - eggs
- string:String
  integer: 100000
  decimal: 999.999
  boolean: false
  date: 2020-01-01
  timestamp: 2020-01-01T00:00:00.123456789+09:00
  nullonly: null
  object:
    hoge:Hoge
    fuga:Fuga
  array:
  -Huh
  -Bah
  -Bazu
  - -spam
    -Ham
    -Egg

**********Convert YAML to Java object**********
key: value (java.lang.String)
foo: bar (java.lang.String)
hoge: fuga (java.lang.String)
datalist: (java.util.ArrayList)
  (java.util.LinkedHashMap)
    string: mojiretu (java.lang.String)
    integer: 123456 (java.lang.Integer)
    decimal: 123.456 (java.lang.Double)
    boolean: true (java.lang.Boolean)
    date: Wed Jan 01 09:00:00 JST 2020 (java.util.Date)
    timestamp: Wed Jan 01 00:00:00 JST 2020 (java.util.Date)
    nullonly: null
    object: (java.util.LinkedHashMap)
      hoge: HOGE (java.lang.String)
      fuga: FUGA (java.lang.String)
    array: (java.util.ArrayList)
      foo (java.lang.String)
      bar (java.lang.String)
      baz (java.lang.String)
      (java.util.ArrayList)
        spam (java.lang.String)
        ham (java.lang.String)
        eggs (java.lang.String)
  (java.util.LinkedHashMap)
    string:String(java.lang.String)
    integer: 100000 (java.lang.Integer)
    decimal: 999.999 (java.lang.Double)
    boolean: false (java.lang.Boolean)
    date: Wed Jan 01 09:00:00 JST 2020 (java.util.Date)
    timestamp: Wed Jan 01 00:00:00 JST 2020 (java.util.Date)
    nullonly: null
    object: (java.util.LinkedHashMap)
      hoge:Hoge(java.lang.String)
      fuga:Fuga(java.lang.String)
    array: (java.util.ArrayList)
Huh(java.lang.String)
Bah(java.lang.String)
Bazu(java.lang.String)
      (java.util.ArrayList)
spam(java.lang.String)
Ham(java.lang.String)
Egg(java.lang.String)
**********Convert Java objects to JSON**********
{
  "key" : "value",
  "foo" : "bar",
  "hoge" : "fuga",
  "datalist" : [ {
    "string" : "mojiretu",
    "integer" : 123456,
    "decimal" : 123.456,
    "boolean" : true,
    "date" : 1577836800000,
    "timestamp" : 1577804400123,
    "nullonly" : null,
    "object" : {
      "hoge" : "HOGE",
      "fuga" : "FUGA"
    },
    "array" : [ "foo", "bar", "baz", [ "spam", "ham", "eggs" ] ]
  }, {
    "string" : "String",
    "integer" : 100000,
    "decimal" : 999.999,
    "boolean" : false,
    "date" : 1577836800000,
    "timestamp" : 1577804400123,
    "nullonly" : null,
    "object" : {
      "hoge" : "Hoge",
      "fuga" : "Fuga"
    },
    "array" : [ "Huh", "Bah", "Bazu", [ "spam", "Ham", "Egg" ] ]
  } ]
}

Reference material

JSON + Jackson

• RFC 8259 - The JavaScript Object Notation (JSON) Data Interchange Format
• GitHub - FasterXML/jackson: Main Portal page for the Jackson project
• jackson-core 2.11.3 javadoc (com.fasterxml.jackson.core)
• jackson-databind 2.11.3 javadoc (com.fasterxml.jackson.core)

YAML + SnakeYAML

• YAML Ain’t Markup Language (YAML™) Version 1.1
• Timestamp Language-Independent Type for YAML™ Version 1.1
• asomov / snakeyaml — Bitbucket
• snakeyaml 1.27 javadoc (org.yaml)