鸿蒙操作系统（HarmonyOS）作为华为推出的面向全场景的分布式操作系统，其文件下载与上传功能在实际开发中是非常重要的部分。本文将深入探讨如何在鸿蒙系统中实现文件的下载和上传，并提供一些实战技巧。
文件下载的核心是通过HTTP或HTTPS协议从远程服务器获取数据并保存到本地存储。鸿蒙支持使用HttpURLConnection或第三方库（如OkHttp）来完成这一任务。
以下是文件下载的主要步骤：
以下是一个基于HttpURLConnection的文件下载代码片段：
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
public class FileDownloader {
public static void downloadFile(String fileUrl, String destinationPath) throws IOException {
URL url = new URL(fileUrl);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000); // 设置超时时间
connection.setReadTimeout(5000);
int responseCode = connection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
InputStream inputStream = connection.getInputStream();
FileOutputStream outputStream = new FileOutputStream(destinationPath);
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, bytesRead);
}
outputStream.close();
inputStream.close();
} else {
throw new IOException("Failed to download file. Server returned HTTP " + responseCode);
}
connection.disconnect();
}
}
为了支持断点续传，需要在请求头中添加Range字段，指定从哪个字节开始下载。例如：
long downloadedBytes = ...; // 已下载的字节数
connection.setRequestProperty("Range", "bytes=" + downloadedBytes + "-");
文件上传通常是将本地文件发送到服务器的过程，常见的方法包括表单上传（multipart/form-data）和二进制流上传。
表单上传适用于需要同时上传文件和其他参数的场景。
以下是一个基于HttpURLConnection的表单上传代码：
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
public class FileUploader {
private static final String boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW";
private static final String lineEnd = "\r\n";
private static final String twoHyphens = "--";
public static void uploadFile(String requestUrl, String filePath, String paramName) throws IOException {
File file = new File(filePath);
URL url = new URL(requestUrl);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setUseCaches(false);
connection.setRequestMethod("POST");
connection.setRequestProperty("Connection", "Keep-Alive");
connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
OutputStream outputStream = connection.getOutputStream();
PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream, "UTF-8"), true);
// 添加文件参数
writer.append(twoHyphens + boundary).append(lineEnd)
.append("Content-Disposition: form-data; name=\"" + paramName + "\"; filename=\"" + file.getName() + "\"")
.append(lineEnd)
.append("Content-Type: " + URLConnection.guessContentTypeFromName(file.getName()))
.append(lineEnd)
.append(lineEnd)
.flush();
FileInputStream inputStream = new FileInputStream(file);
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, bytesRead);
}
outputStream.flush();
inputStream.close();
writer.append(lineEnd).flush(); // 文件结束符
writer.append(twoHyphens + boundary + twoHyphens).append(lineEnd).flush();
int responseCode = connection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
InputStream responseStream = connection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(responseStream));
String line;
StringBuilder response = new StringBuilder();
while ((line = reader.readLine()) != null) {
response.append(line);
}
System.out.println("Server Response: " + response.toString());
} else {
throw new IOException("Upload failed with HTTP error code: " + responseCode);
}
writer.close();
outputStream.close();
connection.disconnect();
}
}
如果只需要上传文件本身，可以使用二进制流上传，这种方式更高效。
多线程下载
使用多线程技术可以显著提高大文件的下载速度。每个线程负责下载文件的一部分，最后合并成完整文件。
进度条显示
在UI界面上显示下载进度，提升用户体验。可以通过监听输入流读取的字节数来计算进度。
错误处理与重试机制
网络不稳定可能导致下载失败，因此需要实现自动重试机制。例如：
for (int attempt = 0; attempt < maxAttempts; attempt++) {
try {
downloadFile(fileUrl, destinationPath);
break; // 成功后退出循环
} catch (IOException e) {
System.err.println("Attempt " + (attempt + 1) + " failed. Retrying...");
}
}
文件校验
下载完成后，可以通过MD5或SHA-256等算法校验文件完整性，确保文件未被篡改。
权限管理
确保应用已申请网络访问和文件存储权限。对于鸿蒙系统，可以在config.json中声明相关权限：
{
"reqPermissions": [
{"name": "ohos.permission.INTERNET"},
{"name": "ohos.permission.READ_EXTERNAL_STORAGE"},
{"name": "ohos.permission.WRITE_EXTERNAL_STORAGE"}
]
}
本文详细介绍了鸿蒙系统中文件下载与上传的技术实现，包括基本原理、代码示例以及实战技巧。通过合理使用多线程、断点续传、进度条显示等功能，可以大幅提升用户体验和程序性能。