RandomController.java

import org.springframework.boot.json.BasicJsonParser;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import java.util.Map;
import java.util.Random;

import static org.springframework.http.HttpMethod.POST;
import static org.springframework.web.bind.annotation.RequestMethod.GET;

@RestController
public class RandomController {

    private final Random random;

    public RandomController(Random random) {
        this.random = random;
    }

    @RequestMapping(value = "/get", method = GET)
    public int random(@RequestParam(value = "limit", defaultValue = "100") int limit) {
        String bearerToken = getBearerToken();
        int[] bounds = getBounds(bearerToken);
        return computeRandom(bounds[0], bounds[1]);
    }

    private String getBearerToken() {
        RestTemplate tokenTemplate = new RestTemplate();
        MultiValueMap<String, String> body = new LinkedMultiValueMap<>();
        body.add("client_id", "my id");
        body.add("client_secret", "my secret");
        body.add("grant_type", "client_credentials");
        HttpHeaders headers = new HttpHeaders();
        headers.add("Accept", "application/json");
        HttpEntity<?> entity = new HttpEntity<>(body, headers);
        ResponseEntity<String> res = tokenTemplate.exchange(
                "https://bearer.token/get", POST, entity, String.class);
        Map<String, Object> map = new BasicJsonParser().parseMap(res.getBody());
        return (String) map.get("access_token");
    }

    private int[] getBounds(String bearerToken) {
        RestTemplate configurationTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.add("Authorization", "Bearer " + bearerToken);
        HttpEntity<?> entity = new HttpEntity<>(headers);
        ResponseEntity<String> res = configurationTemplate.exchange(
                "https://configurations.com/bounds", HttpMethod.GET, entity, String.class);
        Map<String, Object> map = new BasicJsonParser().parseMap(res.getBody());
        Map<String, Long> value = (Map<String, Long>) map.get("value");
        int lowerBound = value.get("lower").intValue();
        int upperBound = value.get("upper").intValue();
        return new int[]{lowerBound, upperBound};
    }

    private int computeRandom(int lowerBound, int upperBound) {
        int difference = upperBound - lowerBound;
        int raw = random.nextInt(difference);
        return raw + lowerBound;
    }
}