JavaとSpring Bootで為替レートを取得する

package com.example.fx;

import com.fasterxml.jackson.annotation.JsonProperty;
import java.math.BigDecimal;
import java.time.Instant;
import java.util.Map;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.HttpHeaders;
import org.springframework.stereotype.Component;
import org.springframework.web.client.RestClient;

record LatestRates(
    String base,
    String source,
    @JsonProperty("market_session") String marketSession,
    @JsonProperty("data_updated_at") Instant dataUpdatedAt,
    Map<String, BigDecimal> rates
) {}

@Component
public final class ExchangeRateClient {
  private final RestClient client;

  public ExchangeRateClient(
      RestClient.Builder builder,
      @Value("${exchangerate.api-key}") String apiKey
  ) {
    this.client = builder
        .baseUrl("https://api.exchangerate.dev/v1")
        .defaultHeader(HttpHeaders.AUTHORIZATION, "Bearer " + apiKey)
        .build();
  }

  public LatestRates latest(String base) {
    return client.get()
        .uri("/latest/{base}?symbols=EUR,GBP", base)
        .retrieve()
        .body(LatestRates.class);
  }
}

exchangerate:
  api-key: ${EXCHANGERATE_API_KEY}