java 如何下载链接文件

你可以使用 Java 中的 `java.net.URL` 和 `java.net.HttpURLConnection` 类来下载链接文件。以下是一个示例代码：

import java.io.*;
import java.net.*;

public class FileDownloader {
    public static void download(String fileUrl, String saveAsFileName) throws IOException {
        URL url = new URL(fileUrl);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");

        int responseCode = connection.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            InputStream inputStream = connection.getInputStream();
            FileOutputStream outputStream = new FileOutputStream(saveAsFileName);

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

            outputStream.close();
            inputStream.close();
            System.out.println("File downloaded successfully.");
        } else {
            System.out.println("Failed to download file.");
        }
    }

    public static void main(String[] args) {
        String fileUrl = "https://example.com/myfile.txt";
        String saveAsFileName = "myfile.txt";

        try {
            download(fileUrl, saveAsFileName);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在此代码中，我们首先创建一个 `URL` 对象来表示文件的链接，然后使用 `HttpURLConnection` 对象打开连接并设置请求方法为 `GET`。我们检查响应代码是否为 `HTTP_OK`，如果是，则将链接文件的输入流复制到本地文件的输出流中。最后，我们关闭输入和输出流并打印成功消息。