Java中可以使用URL類來發送HTTP請求并獲取響應。在訪問API時，一般都會返回JSON格式的數據。下面是一個簡單的示例代碼：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
public class JsonFromUrl {
public static void main(String[] args) throws IOException {
String apiUrl = "https://api.com/data.json";
URL url = new URL(apiUrl);
URLConnection connection = url.openConnection();
BufferedReader reader = new BufferedReader(new InputStreamReader(
connection.getInputStream()));
String line;
StringBuilder builder = new StringBuilder();
while ((line = reader.readLine()) != null) {
builder.append(line);
}
String json = builder.toString();
System.out.println(json);
}
}

該代碼簡單地通過URL類打開鏈接并讀取響應。BufferedReader逐行讀取響應，并將每行數據添加到StringBuilder中。最后，將StringBuilder轉換為字符串形式的JSON響應，然后打印出來。