Parse nested JSON in Java

Question

I just wanted to ask, how to simply parse nested JSON structure in Java that looks like this:

{
   "goods":{
      "NY Store":[
         {
            "product":"Teddybear",
            "available":"20"
         },
         {
            "product":"Mountain bike",
            "available":"0"
         }]
      "LA Store":[
         {
            "product": ....and so on

I want to get all the products from all the stores, but the list is quite big (200 stores). Any tips and hints, please?

No, I only need to get product name + availibility as 2 Strings and then push tem into a hashmap. — Droidik
– Droidik, Commented May 5, 2012 at 0:56
That's not "nested JSON", that's plain old JSON. You just parse it. You can use a fancy-dancy Jacksonesque tool to parse into "POJOs", but you first should learn to just use a simple parser to parse it into Maps and Lists, the navigate through the Maps and Lists to access your data. This way you'll come to understand JSON much better. — Hot Licks
– Hot Licks, Commented Sep 27, 2014 at 1:34
You'd parse the above into a JSONObject, call it root, then do root.getObject("goods") to go the first level, producing another JSONObject (call it goods). Then goods.getArray("NY Store") to get a JSONArray called store. Then store.getObject(0) to get the first element of the array called storeElement, then storeElement.getString("product") will return "Teddybear". About 5 lines to fetch "Teddybear", if you put each step on a single line (which is advised, when you're starting out). — Hot Licks
– Hot Licks, Commented Sep 27, 2014 at 1:40
BTW, go to json.org and study the JSON syntax -- it only takes 5- 10 minutes to learn. — Hot Licks
– Hot Licks, Commented Sep 27, 2014 at 1:41

Krrose27 · Accepted Answer · 2012-05-05 01:14:23Z

This is a quick intro for your specific use case into the Jackson library.

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

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.annotate.JsonSerialize;

public class JSONTest {
    /**
     * @param args
     * @throws IOException
     * @throws JsonMappingException
     * @throws JsonGenerationException
     */
    public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {
        HashMap<String, ArrayList<InventoryItem>> fs = new HashMap<String, ArrayList<InventoryItem>>();
        for (int i = 0; i < 5; i++) {
            ArrayList<InventoryItem> its = new ArrayList<InventoryItem>();
            its.add(new InventoryItem("teddy", 20));
            its.add(new InventoryItem("diny", 10));
            fs.put(Long.toString(System.nanoTime()), its);
        }
        StoreContianer g = new StoreContianer(fs);
        ObjectMapper objm = new ObjectMapper();
        StringWriter sw = new StringWriter();
        objm.writeValue(sw, g);
        System.out.println(sw.toString());
        StoreContianer c = objm.readValue(
                "{\"goods\":{\"55278650620460\":[{\"product\":\"teddy\",\"available\":20},{\"product\":\"diny\",\"available\":10}],\"55278650631327\":[{\"product\":\"teddy\",\"available\":20},{\"product\":\"diny\",\"available\":10}],\"55278650628131\":[{\"product\":\"teddy\",\"available\":20},{\"product\":\"diny\",\"available\":10}],\"55278650582748\":[{\"product\":\"teddy\",\"available\":20},{\"product\":\"diny\",\"available\":10}],\"55278650624615\":[{\"product\":\"teddy\",\"available\":20},{\"product\":\"diny\",\"available\":10}]}}",
                StoreContianer.class);
        StringWriter sw2 = new StringWriter();
        objm.writeValue(sw2, c);
        System.out.println(sw2.toString());
    }
}

@JsonSerialize
class StoreContianer {
    private final HashMap<String, ArrayList<InventoryItem>> goods;

    public StoreContianer(@JsonProperty("goods") HashMap<String, ArrayList<InventoryItem>> goods) {
        this.goods = goods;
    }

    public HashMap<String, ArrayList<InventoryItem>> getGoods() {
        return goods;
    }
}

@JsonSerialize
class InventoryItem {
    private final String product;
    private final int available;

    public InventoryItem(@JsonProperty("product") String product, @JsonProperty("available") int available) {
        this.product = product;
        this.available = available;
    }

    public String getProduct() {
        return product;
    }

    public int getAvailable() {
        return available;
    }
}

jcomeau_ictx · Accepted Answer · 2012-05-05 00:48:58Z

1

why not use the library? http://www.json.org/java/

specifically,

public JSONObject(String source) throws JSONException {
        this(new JSONTokener(source));
}

answered May 5, 2012 at 0:48

jcomeau_ictx

38.6k7 gold badges98 silver badges114 bronze badges

9 Comments

Matt Ball Over a year ago

Meh, that JSON library is pretty lousy for Java. There are much better ones out there, such as GSON or Jackson.

Droidik Over a year ago

I tried to iterate through the JSONArray object, but it didn't work. JSONObject goods = new JSONObject(jsonInput); JSONArray stores = goods.toJSONArray("stores"); throws me an error

jcomeau_ictx Over a year ago

need more information, update your question with some details from this attempt.

Lukas Hanacek Over a year ago

because it is incredible slow

Paul Over a year ago

@MattBall It's not a lousy library; its usefulness depends on what's needed. The JSON in Java library does not require deserializing to a custom class - basic operations are performed using the post-parsing JSONObject which is all the OP needed. If I'm working with a response from a web service then I'll use Jackson and unmarhsal to my own classes but if I need a quick way to manipulate a JSON object directly (and not through my own POJO) I use the JSON in Java library.

|

Usman Chaudhri · Accepted Answer · 2014-09-27 00:59:12Z

0

I found this google library very powerful for parsing nested objects in JSON.

List<String> products = JsonPath.read(json, "$.goods.NY Store[*].product");

This will return you a list of all products in each "NY Store" list.

edited Sep 27, 2014 at 0:59

user3141031

answered Sep 27, 2014 at 0:31

Usman Chaudhri

1

Comments

Mateo · Accepted Answer · 2019-10-02 21:26:19Z

    //import java.util.ArrayList;
    //import org.bson.Document;

    Document root = Document.parse("{\n"
            + "   \"goods\":{\n"
            + "      \"NY Store\":[\n"
            + "         {\n"
            + "            \"product\":\"Teddybear\",\n"
            + "            \"available\":\"20\"\n"
            + "         },\n"
            + "         {\n"
            + "            \"product\":\"Mountain bike\",\n"
            + "            \"available\":\"0\"\n"
            + "         }]}}");

    System.out.println(((String) ((Document) ((ArrayList) ((Document) root.get("goods")).get("NY Store")).get(0)).get("product")));
    System.out.println(((String) ((Document) ((ArrayList) ((Document) root.get("goods")).get("NY Store")).get(0)).get("available")));
    System.out.println(((String) ((Document) ((ArrayList) ((Document) root.get("goods")).get("NY Store")).get(1)).get("product")));
    System.out.println(((String) ((Document) ((ArrayList) ((Document) root.get("goods")).get("NY Store")).get(1)).get("available")));

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