UUIDFetch.java

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

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.UUID;

/**
 * Created by Yonas on 20.10.2015.
 */
public class UUIDProfile {

    private JSONObject result;

    private String name;
    private UUID identifier;

    private List<String> history = new ArrayList<String>();

    private boolean isPremium;

    public UUIDProfile(JSONObject result) {
        this.result = result;

        this.work();
    }

    public String getName() {
        return this.name;
    }

    public UUID getIdentifier() {
        return this.identifier;
    }

    public boolean isPremium() {
        return this.isPremium;
    }

    public List<String> getHistory() {
        return this.history;
    }

    /**
     * Uses the results to put them into the attributes.
     */
    private void work() {

        if(((JSONObject )this.result.get("result")).get("status").toString().equalsIgnoreCase("error")) {
            return;
        }

        String username = this.result.get("username").toString();
        UUID formatUUID = UUID.fromString(this.result.get("uuid").toString().replaceFirst("([0-9a-fA-F]{8})([0-9a-fA-F]{4})([0-9a-fA-F]{4})([0-9a-fA-F]{4})([0-9a-fA-F]+)", "$1-$2-$3-$4-$5"));
        this.isPremium = Boolean.valueOf(this.result.get("premium").toString());

        Iterator<JSONObject> history = ((JSONArray) this.result.get("history")).iterator();

        while(history.hasNext()) {

            this.history.add(history.next().get("name").toString());

        }


    }

}

UUIDProfile.java

import org.bukkit.entity.Player;
import org.json.simple.JSONObject;
import org.json.simple.JSONValue;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.UUID;

/**
 * Created by Yonas on 20.10.2015.
 */
public class UUIDFetcher {

    private final static String API_ENDPOINT = "http://mcapi.de/api/user/%s";

    public static UUIDProfile getProfile(UUID uuid) throws IOException {
        return UUIDFetcher.getProfile(uuid.toString());
    }

    public static UUIDProfile getProfile(Player player) throws IOException {
        return UUIDFetcher.getProfile(player.getName());
    }

    public static UUIDProfile getProfile(String playerName) throws IOException {
        return new UUIDProfile(
                UUIDFetcher.fetch(new URL(String.format(UUIDFetcher.API_ENDPOINT, playerName)))
        );
    }

    private static JSONObject fetch(URL url) throws IOException {
        StringBuilder jsonString = new StringBuilder();
        InputStream inputStream = url.openStream();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

        String line;
        while ((line = bufferedReader.readLine()) != null) {
            jsonString.append(line);
        }

        inputStream.close();
        bufferedReader.close();
        //--------
        JSONObject jsonObject = (JSONObject)((JSONObject) JSONValue.parse(jsonString.toString()));

        return jsonObject;
    }

}

You should probably use for loops on line 44. Makes it a bit cleaner.

@blackwolf12333 You're right. Well... after this long time I updated it.