Java - get JSON data from URL

Question

I'm trying to pull a JSON document from http://api.conceptnet.io/c/en/concept but I haven't been successful in getting the JSON data into a variable. All I've managed to do is to get the page's source (specifically just the first line, but I understand why I only get one line) with:

InputStream stream = url.openStream();
Scanner scan = new Scanner(stream);
String data = scan.nextLine();
System.out.println(data);

Which isn't helpful. If I could get the JSON data into a String, I can feed that into a JSONObject constructor to build the JSONObject. If I were doing this in python, all I would have to do is:

concept = requests.get('http://api.conceptnet.io/c/en/' + theword).json()

But I can't figure out the equivalent for that in Java. I have very little experience with web requests so I appreciate any help.

You can use ObjectMapper or JsonObject to parse the response body into a Json. — codeogeek
– codeogeek, Commented Jun 8, 2020 at 17:59
So, your problem is to bring data or to change json string to json object? — KunLun
– KunLun, Commented Jun 8, 2020 at 18:00
@KunLun I'm trying to get the data from the website. JSONObject has a constructor that accepts a string to turn into a JSONObject. — Robobot1747
– Robobot1747, Commented Jun 8, 2020 at 18:04

sameera sy · Accepted Answer · 2020-06-08 18:10:39Z

1

However pythonic way seems much easier, it can't get more easy in Java than this.

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder().uri(URI.create("http://api.conceptnet.io/c/en/concept")).build();

HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
JSONObject myObject = new JSONObject(response.body());
System.out.println(myObject); // Your json object

Don't forget to add the dependencies below.

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import org.json.JSONObject;

Dependency for org.json can be found here : https://mvnrepository.com/artifact/org.json/json

answered Jun 8, 2020 at 18:10

sameera sy

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jøkęr · Accepted Answer · 2020-06-08 18:13:32Z

1

There are multiple options to get a json in java.

If you are using Java 11, you can use Java in built web client.


    HttpClient client = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
      .uri(URI.create("http://api.conceptnet.io/c/en/concept"))
      .build();
    client.sendAsync(request, BodyHandlers.ofString())
      .thenApply(HttpResponse::body)
      .thenAccept(System.out::println)
      .join();

Using a library like OkHttp, you have to create a request and feed it to the HttpClient.


    Request request = new Request
       .Builder()
       .url("http://api.conceptnet.io/c/en/concept")
       .get()
       .build()

    OkHttpClient httpClient = client.newBuilder().build()
    Response response = httpClient.newCall(request).execute()
    System.out.println(response.body.string())

answered Jun 8, 2020 at 18:13

jøkęr

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4 Comments

Robobot1747 Over a year ago

Thanks for the help. Do you happen to know where I could download the library for OkHTTP? I can't seem to find any official source for it. Thanks!

jøkęr Over a year ago

OkHttp If you are using a build tool like maven or gradle you can add it as a dependency.

Robobot1747 Over a year ago

I found the .jar and added it to my build path but when I run a program similar to yours I get a NoClassDefFoundError. I looked that up and an example situation for that was removing a .class file after compilation, which I didn't do. Do you have any idea what's wrong?

jøkęr Over a year ago

Difficult to say without looking at the code and your setup, but it seems like the jar was not loaded.

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