在Java中，可以使用以下方式實現文件下載：

1. 使用URL和URLConnection類：可以通過創建URL對象，然后打開連接并獲取輸入流，將輸入流寫入輸出流實現文件下載。

URL url = new URL(fileUrl);
HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
InputStream inputStream = httpConn.getInputStream();
FileOutputStream outputStream = new FileOutputStream(localFilePath);

int bytesRead;
byte[] buffer = new byte[4096];
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
}

outputStream.close();
inputStream.close();

2. 使用Apache HttpClient庫：可以使用HttpClient庫來簡化文件下載過程，通過HttpGet請求獲取文件內容并保存到本地文件。

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(fileUrl);
CloseableHttpResponse response = httpClient.execute(httpGet);

HttpEntity entity = response.getEntity();
if (entity != null) {
    InputStream inputStream = entity.getContent();
    FileOutputStream outputStream = new FileOutputStream(localFilePath);

    int bytesRead;
    byte[] buffer = new byte[4096];
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, bytesRead);
    }

    outputStream.close();
    inputStream.close();
}

httpClient.close();

3. 使用Files類：Java 7引入了Files類，可以使用它的copy()方法實現文件的下載。

URL url = new URL(fileUrl);
InputStream inputStream = url.openStream();
Files.copy(inputStream, Paths.get(localFilePath), StandardCopyOption.REPLACE_EXISTING);

這些方式都可以用來實現文件下載，可以根據具體需求選擇合適的方式。