How to parse JSON in Java

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Top 5 Answer for How to parse JSON in Java

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93

The org.json library is easy to use.

Just remember (while casting or using methods like getJSONObject and getJSONArray) that in JSON notation

  • [ … ] represents an array, so library will parse it to JSONArray
  • { … } represents an object, so library will parse it to JSONObject

Example code below:

import org.json.*;  String jsonString = ... ; //assign your JSON String here JSONObject obj = new JSONObject(jsonString); String pageName = obj.getJSONObject("pageInfo").getString("pageName");  JSONArray arr = obj.getJSONArray("posts"); // notice that `"posts": [...]` for (int i = 0; i < arr.length(); i++) {     String post_id = arr.getJSONObject(i).getString("post_id");     ...... } 

You may find more examples from: Parse JSON in Java

Downloadable jar: http://mvnrepository.com/artifact/org.json/json

vote vote

86

For the sake of the example lets assume you have a class Person with just a name.

private class Person {     public String name;      public Person(String name) {         this.name = name;     } } 

Google GSON (Maven)

My personal favourite as to the great JSON serialisation / de-serialisation of objects.

Gson g = new Gson();  Person person = g.fromJson("{\"name\": \"John\"}", Person.class); System.out.println(person.name); //John  System.out.println(g.toJson(person)); // {"name":"John"} 

Update

If you want to get a single attribute out you can do it easily with the Google library as well:

JsonObject jsonObject = new JsonParser().parse("{\"name\": \"John\"}").getAsJsonObject();  System.out.println(jsonObject.get("name").getAsString()); //John 

Org.JSON (Maven)

If you don't need object de-serialisation but to simply get an attribute, you can try org.json (or look GSON example above!)

JSONObject obj = new JSONObject("{\"name\": \"John\"}");  System.out.println(obj.getString("name")); //John 

Jackson (Maven)

ObjectMapper mapper = new ObjectMapper(); Person user = mapper.readValue("{\"name\": \"John\"}", Person.class);  System.out.println(user.name); //John 
vote vote

72

  1. If one wants to create Java object from JSON and vice versa, use GSON or JACKSON third party jars etc.

    //from object to JSON  Gson gson = new Gson(); gson.toJson(yourObject);  // from JSON to object  yourObject o = gson.fromJson(JSONString,yourObject.class); 
  2. But if one just want to parse a JSON string and get some values, (OR create a JSON string from scratch to send over wire) just use JaveEE jar which contains JsonReader, JsonArray, JsonObject etc. You may want to download the implementation of that spec like javax.json. With these two jars I am able to parse the json and use the values.

    These APIs actually follow the DOM/SAX parsing model of XML.

    Response response = request.get(); // REST call      JsonReader jsonReader = Json.createReader(new StringReader(response.readEntity(String.class)));     JsonArray jsonArray = jsonReader.readArray();     ListIterator l = jsonArray.listIterator();     while ( l.hasNext() ) {           JsonObject j = (JsonObject)l.next();           JsonObject ciAttr = j.getJsonObject("ciAttributes"); 
vote vote

69

quick-json parser is very straightforward, flexible, very fast and customizable. Try it

Features:

  • Compliant with JSON specification (RFC4627)
  • High-Performance JSON parser
  • Supports Flexible/Configurable parsing approach
  • Configurable validation of key/value pairs of any JSON Hierarchy
  • Easy to use # Very small footprint
  • Raises developer friendly and easy to trace exceptions
  • Pluggable Custom Validation support - Keys/Values can be validated by configuring custom validators as and when encountered
  • Validating and Non-Validating parser support
  • Support for two types of configuration (JSON/XML) for using quick-JSON validating parser
  • Requires JDK 1.5
  • No dependency on external libraries
  • Support for JSON Generation through object serialisation
  • Support for collection type selection during parsing process

It can be used like this:

JsonParserFactory factory=JsonParserFactory.getInstance(); JSONParser parser=factory.newJsonParser(); Map jsonMap=parser.parseJson(jsonString); 
vote vote

57

You could use Google Gson.

Using this library you only need to create a model with the same JSON structure. Then the model is automatically filled in. You have to call your variables as your JSON keys, or use @SerializedName if you want to use different names.

JSON

From your example:

{     "pageInfo": {         "pageName": "abc",         "pagePic": "http://example.com/content.jpg"     }     "posts": [         {             "post_id": "123456789012_123456789012",             "actor_id": "1234567890",             "picOfPersonWhoPosted": "http://example.com/photo.jpg",             "nameOfPersonWhoPosted": "Jane Doe",             "message": "Sounds cool. Can't wait to see it!",             "likesCount": "2",             "comments": [],             "timeOfPost": "1234567890"         }     ] } 

Model

class MyModel {      private PageInfo pageInfo;     private ArrayList<Post> posts = new ArrayList<>(); }  class PageInfo {      private String pageName;     private String pagePic; }  class Post {      private String post_id;      @SerializedName("actor_id") // <- example SerializedName     private String actorId;      private String picOfPersonWhoPosted;     private String nameOfPersonWhoPosted;     private String message;     private String likesCount;     private ArrayList<String> comments;     private String timeOfPost; } 

Parsing

Now you can parse using Gson library:

MyModel model = gson.fromJson(jsonString, MyModel.class); 

Gradle import

Remember to import the library in the app Gradle file

implementation 'com.google.code.gson:gson:2.8.6' // or earlier versions 

Automatic model generation

You can generate model from JSON automatically using online tools like this.

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