要自定義Java requests的請求頭，可以使用URLConnection或HttpClient來發送HTTP請求，并設置請求頭。以下是使用URLConnection和HttpClient分別自定義請求頭的示例代碼：

1. 使用URLConnection自定義請求頭：

import java.net.HttpURLConnection;
import java.net.URL;

public class CustomRequestHeader {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://api.example.com");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            
            // 設置請求頭
            conn.setRequestProperty("Authorization", "Bearer token");
            conn.setRequestProperty("Content-Type", "application/json");
            
            // 發送請求
            conn.setRequestMethod("GET");
            int responseCode = conn.getResponseCode();
            
            System.out.println("Response Code: " + responseCode);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2. 使用HttpClient自定義請求頭：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;

public class CustomRequestHeader {
    public static void main(String[] args) {
        try {
            HttpClient httpClient = HttpClientBuilder.create().build();
            HttpGet httpGet = new HttpGet("https://api.example.com");
            
            // 設置請求頭
            httpGet.addHeader("Authorization", "Bearer token");
            httpGet.addHeader("Content-Type", "application/json");
            
            // 發送請求
            HttpResponse response = httpClient.execute(httpGet);
            
            System.out.println("Response Code: " + response.getStatusLine().getStatusCode());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

以上代碼示例分別使用URLConnection和HttpClient發送HTTP請求，并設置了Authorization和Content-Type兩個自定義請求頭。你可以根據需要自定義更多的請求頭參數。