方式一（适用于小型文件）

• 代码示例

  import java.io.FileOutputStream;
  import java.net.URL;
  import java.nio.channels.Channels;
  import java.nio.channels.ReadableByteChannel;
  
  public class FileDownloader {
      public static void downloadFile(String remoteFilePath, String localFilePath) {
          try {
              URL website = new URL(remoteFilePath);
              ReadableByteChannel rbc = Channels.newChannel(website.openStream());
              FileOutputStream fos = new FileOutputStream(localFilePath);
              fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
              fos.close();
              rbc.close();
              System.out.println("文件下载完成！");
          } catch (Exception e) {
              e.printStackTrace();
          }
      }
      public static void main(String[] args) {
          downloadFile("https://example.com/file.pdf", "D:/file.pdf");
      }
  }

方式二（适用于大型文件）

• 代码示例

  import java.io.*;
  import java.net.HttpURLConnection;
  import java.net.URL;
  
  public class LargeFileDownloader {
      public static void downloadLargeFile(String downloadUrl, String savePath) {
          InputStream inputStream = null;
          OutputStream outputStream = null;
          try {
              URL url = new URL(downloadUrl);
              HttpURLConnection connection = (HttpURLConnection) url.openConnection();
              connection.setConnectTimeout(3000);
              connection.setRequestProperty("User-Agent", "Mozilla/4.0");
              inputStream = new BufferedInputStream(connection.getInputStream());
              File file = new File(savePath);
              if (file.exists()) file.delete();
              outputStream = new FileOutputStream(file);
              byte[] buffer = new byte[1024 * 1024 * 5]; // 5MB 缓冲区
              int len;
              while ((len = inputStream.read(buffer)) != -1) {
                  outputStream.write(buffer, 0, len);
              }
              System.out.println("文件下载完成！");
          } catch (Exception e) {
              e.printStackTrace();
          } finally {
              try { if (outputStream != null) outputStream.close(); } catch (IOException ignored) {}
              try { if (inputStream != null) inputStream.close(); } catch (IOException ignored) {}
          }
      }
      public static void main(String[] args) {
          downloadLargeFile("https://example.com/largefile.zip", "D:/largefile.zip");
      }
  }

• 特点：使用缓冲流分块读取，适合大文件，避免一次性加载文件到内存导致内存溢出的问题