Multithreaded client-server with oxford dictionary api, JSON parsing using json-simple: https://code.google.com/archive/p/json-simple/downloads

Client.java

import java.io.*;
import java.net.Socket;
import java.util.Scanner;

/**
 * Created by ahmedengu.
 */
public class Client {

    public static void main(String[] args) {

        try {
            Socket client = new Socket("localhost", 1234);

            System.out.println("Just connected to " + client.getRemoteSocketAddress());
            Scanner scanner = new Scanner(System.in);
            DataOutputStream out = new DataOutputStream(client.getOutputStream());
            DataInputStream in = new DataInputStream(client.getInputStream());
            System.out.println("Write a word[-1 to exit]:");
            String read = scanner.nextLine();
            out.writeUTF(read);
            while (!read.contains("-1")) {
                System.out.println(in.readUTF());
                System.out.println("Write a word[-1 to exit]:");
                read = scanner.nextLine();
                out.writeUTF(read);
            }
            client.close();
            System.out.println("Disconnected");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Oxford.java

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;

import javax.net.ssl.HttpsURLConnection;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;

/**
 * Created by ahmedengu.
 */
public class Oxford {
    public static Oxford instance;

    private Oxford() {
    }

    public static Oxford getInstance() {
        if (instance == null) {
            synchronized (Oxford.class) {
                if (instance == null)
                    instance = new Oxford();
            }
        }
        return instance;
    }

    public String dictionary(String word) {
        JSONParser parser = new JSONParser();
        String ret = "404";
        try {
            final String result = getRequest(buildURL(word));
            final Object parse = parser.parse(result);
            ret = (String) ((JSONArray) ((JSONObject) ((JSONArray) ((JSONObject) ((JSONArray) ((JSONObject) ((JSONArray) ((JSONObject) ((JSONArray) ((JSONObject) parse).get("results")).get(0)).get("lexicalEntries")).get(0)).get("entries")).get(0)).get("senses")).get(0)).get("definitions")).get(0);
        } catch (Exception e) {
            System.out.println(e);
        }
        return ret;
    }

    private String buildURL(final String word) {
        final String language = "en";
        final String word_id = word.toLowerCase(); //word id is case sensitive and lowercase is required
        return "https://od-api.oxforddictionaries.com:443/api/v1/entries/" + language + "/" + word_id;
    }

    private String getRequest(String link) {
        final String app_id = "2f0d7a3a";
        final String app_key = "5215f3131a55b7cdabb65c4193c63d49";
        try {
            URL url = new URL(link);
            HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
            urlConnection.setRequestProperty("Accept", "application/json");
            urlConnection.setRequestProperty("app_id", app_id);
            urlConnection.setRequestProperty("app_key", app_key);

            // read the output from the server
            BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
            StringBuilder stringBuilder = new StringBuilder();

            String line = null;
            while ((line = reader.readLine()) != null) {
                stringBuilder.append(line + "\n");
            }

            return stringBuilder.toString();
        } catch (Exception e) {
            e.printStackTrace();
            return e.toString();
        }
    }
}

Server.java

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Server extends Thread {
    Socket cSocket;
    static int counter;

    Server(Socket cSocket) {
        this.cSocket = cSocket;
    }

    public static void main(String args[]) throws Exception {
        ServerSocket sSock = new ServerSocket(1234);
        System.out.println("Listening");

        while (true) {
            Socket sock = sSock.accept();
            new Thread(new Server(sock)).start();
        }
    }

    public void run() {
        try {
            System.out.println("Connected " + cSocket.getRemoteSocketAddress() + ", Counter: " + ++counter);
            DataInputStream in = new DataInputStream(cSocket.getInputStream());
            DataOutputStream out = new DataOutputStream(cSocket.getOutputStream());

            String read = in.readUTF();
            while (!read.contains("-1")) {
                out.writeUTF(Oxford.getInstance().dictionary(read));
                read = in.readUTF();
            }

            System.out.println("Disconnected " + cSocket.getRemoteSocketAddress() + ", Counter: " + --counter);
            cSocket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}