如何在Java中模拟文件下载流程 Java通过URL保存资源文件

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Paths;

public class FileDownloader {

    public static void downloadFile(String fileURL, String saveDir, String fileName) throws IOException {
        URL url = new URL(fileURL);
        HttpURLConnection httpConn = null;
        try {
            httpConn = (HttpURLConnection) url.openConnection();
            int responseCode = httpConn.getResponseCode();

            // 检查HTTP响应码，确保是成功的（200 OK）
            if (responseCode == HttpURLConnection.HTTP_OK) {
                String disposition = httpConn.getHeaderField("Content-Disposition");
                String contentType = httpConn.getContentType();
                int contentLength = httpConn.getContentLength();

                System.out.println("Content-Type = " + contentType);
                System.out.println("Content-Disposition = " + disposition);
                System.out.println("Content-Length = " + contentLength);

                // 如果文件名未指定，尝试从Content-Disposition或URL中解析
                if (fileName == null || fileName.trim().isEmpty()) {
                    if (disposition != null && disposition.contains("filename=")) {
                        fileName = disposition.substring(disposition.indexOf("filename=") + 9);
                        if (fileName.contains(";")) { // 处理分号后的额外信息
                            fileName = fileName.substring(0, fileName.indexOf(";"));
                        }
                        fileName = fileName.replace("\"", ""); // 移除可能的引号
                    } else {
                        // 从URL路径中提取文件名
                        fileName = Paths.get(url.getPath()).getFileName().toString();
                    }
                }

                String saveFilePath = saveDir + java.io.File.separator + fileName;
                System.out.println("Saving file to: " + saveFilePath);

                // 获取输入流和输出流
                try (InputStream inputStream = httpConn.getInputStream();
                     FileOutputStream outputStream = new FileOutputStream(saveFilePath)) {

                    byte[] buffer = new byte[4096]; // 4KB 缓冲区
                    int bytesRead = -1;
                    long totalBytesRead = 0;

                    while ((bytesRead = inputStream.read(buffer)) != -1) {
                        outputStream.write(buffer, 0, bytesRead);
                        totalBytesRead += bytesRead;
                        // 可以在这里添加进度更新逻辑，例如：
                        // System.out.print("\rDownloaded: " + totalBytesRead + " bytes");
                    }
                    System.out.println("\nFile downloaded successfully!");
                }
            } else {
                System.out.println("No file to download. Server replied HTTP code: " + responseCode);
            }
        } finally {
            if (httpConn != null) {
                httpConn.disconnect(); // 确保连接被关闭
            }
        }
    }

    public static void main(String[] args) {
        // 示例用法
        String fileURL = "https://www.apache.org/licenses/LICENSE-2.0.txt"; // 替换为你要下载的实际文件URL
        String saveDirectory = "./downloads"; // 替换为你希望保存的目录
        String outputFileName = "ApacheLicense.txt"; // 可以指定文件名，如果为null或空则尝试自动解析

        // 确保下载目录存在
        java.io.File saveDirFile = new java.io.File(saveDirectory);
        if (!saveDirFile.exists()) {
            saveDirFile.mkdirs();
        }

        try {
            downloadFile(fileURL, saveDirectory, outputFileName);
        } catch (IOException ex) {
            System.err.println("Error downloading file: " + ex.getMessage());
            ex.printStackTrace();
        }
    }
}

httpConn.setConnectTimeout(10 * 1000); // 10 seconds
httpConn.setReadTimeout(60 * 1000);    // 60 seconds

// 在下载循环中加入进度更新
long totalBytesRead = 0;
long startTime = System.currentTimeMillis();
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
    totalBytesRead += bytesRead;
    // 每下载一定量数据或者每隔一段时间更新一次进度
    if (System.currentTimeMillis() - startTime > 1000) { // 每秒更新一次
        System.out.printf("\rDownloaded: %.2f MB", (double) totalBytesRead / (1024 * 1024));
        startTime = System.currentTimeMillis(); // 重置计时器
    }
}
System.out.println("\nDownload complete. Total size: " + totalBytesRead + " bytes.");

// 伪代码：分块下载的思路
// public void downloadPart(String url, long startByte, long endByte, String tempFile) {
//     HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
//     conn.setRequestProperty("Range", "bytes=" + startByte + "-" + endByte);
//     // ... 获取输入流，写入 tempFile ...
// }
//
// public void mainDownload(String url, int numThreads) {
//     // 获取文件总大小
//     // 计算每个线程负责的字节范围
//     // 启动多个线程调用 downloadPart
//     // 等待所有线程完成
//     // 合并所有临时文件
// }