代碼：

import org.springframework.http.MediaType;
import org.springframework.http.MediaTypeFactory;

public class Test {

    public static void main(String[] args) {
        String fileName = "1.docx";
        String contentType = MediaTypeFactory.getMediaType(fileName).orElse(MediaType.APPLICATION_OCTET_STREAM).toString();
        System.out.println("文件名稱為“" + fileName + "”的contentType：" + contentType);
    }
}

結果：

文件名稱為“1.docx”的contentType：application/vnd.openxmlformats-officedocument.wordprocessingml.document