前言

Android 10（API 29）及以上启用了 Scoped Storage（分区存储），限制了对外部存储的直接访问

Android < 6.0（API 23）：只需在 AndroidManifest.xml 声明：

1	<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Android 6.0 ~ 9（API 23~28）：除了声明权限，还需动态申请：

1
2
3

if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
}

Android 10+（API 29+）：

默认启用 Scoped Storage，即使有权限也不能随意写入外部存储根目录。

可以使用以下三种方式

// App 私有目录（无需权限，卸载时自动删除）
File privateFile = new File(getFilesDir(), "file.txt");

// App 外部私有目录（无需权限，但可能在外部存储上）
File externalFile = new File(getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), "file.pdf");

// 公共下载目录（需权限 + 适配 Scoped Storage）
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
    // 使用 MediaStore
} else {
    File publicDownload = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
}

或者

使用Scoped Storage

下载工具类

import android.Manifest;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.provider.MediaStore;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;

/**
 * 文件下载工具类，支持 Android 10+ MediaStore 和传统存储方式
 */
public class ZFileDownloader {

    private static final String TAG = "ZFileDownloader";
    private static final int REQUEST_WRITE_PERMISSION = 1001;
    private static final int BUFFER_SIZE = 8192;
    private static final int PROGRESS_UPDATE_INTERVAL = 100; // 进度更新间隔（ms）

    // 复用 OkHttpClient 实例
    private static volatile OkHttpClient sClient;

    @NonNull
    private static OkHttpClient getClient() {
        if (sClient == null) {
            synchronized (ZFileDownloader.class) {
                if (sClient == null) {
                    sClient = new OkHttpClient.Builder()
                            .build();
                }
            }
        }
        return sClient;
    }

    public interface DownloadCallback {
        /**
         * 下载成功（通过 File）
         * 注意：Android 10+ 可能 file == null，建议优先使用 {@link #onSuccess(Uri)}
         */
        void onSuccess(@Nullable File file);

        /**
         * 下载成功（通过 Uri）
         */
        void onSuccess(@NonNull Uri uri);

        /**
         * 下载失败
         */
        void onFailure(@NonNull Exception e);

        /**
         * 下载进度回调
         *
         * @param bytesRead  已读取字节数
         * @param totalBytes 总字节数（如果服务器未返回 content-length，可能为 -1）
         */
        void onProgress(long bytesRead, long totalBytes);
    }

    /**
     * 下载文件到 Downloads 目录
     *
     * @param activity Activity 上下文（用于权限检查和 UI 线程回调）
     * @param url      下载地址
     * @param fileName 保存的文件名
     * @param mimeType 文件 MIME 类型（可为 null，默认 application/octet-stream）
     * @param callback 下载回调
     */
    public static void downloadFile(@NonNull Activity activity,
                                    @NonNull String url,
                                    @NonNull String fileName,
                                    @Nullable String mimeType,
                                    @NonNull DownloadCallback callback) {
        OkHttpClient client = getClient();
        Request request = new Request.Builder()
                .url(url)
                .build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(@NonNull Call call, @NonNull IOException e) {
                activity.runOnUiThread(() -> callback.onFailure(e));
            }

            @Override
            public void onResponse(@NonNull Call call, @NonNull Response response) {
                if (!response.isSuccessful()) {
                    Exception error = new IOException("Response not successful: " + response.code());
                    activity.runOnUiThread(() -> callback.onFailure(error));
                    return;
                }

                ResponseBody body = response.body();
                if (body == null) {
                    Exception error = new IOException("Response body is null");
                    activity.runOnUiThread(() -> callback.onFailure(error));
                    return;
                }

                long totalBytes = body.contentLength();

                try (InputStream inputStream = body.byteStream()) {
                    DownloadResult result = saveFile(activity, inputStream, fileName, mimeType, totalBytes, callback);
                    activity.runOnUiThread(() -> {
                        callback.onSuccess(result.uri);
                        if (result.file != null) {
                            callback.onSuccess(result.file);
                        }
                    });
                } catch (Exception e) {
                    activity.runOnUiThread(() -> callback.onFailure(e));
                }
            }
        });
    }

    /**
     * 保存文件结果
     */
    private static class DownloadResult {
        final Uri uri;
        final File file;

        DownloadResult(@NonNull Uri uri, @Nullable File file) {
            this.uri = uri;
            this.file = file;
        }
    }

    /**
     * 保存文件到本地存储
     */
    private static DownloadResult saveFile(@NonNull Activity activity,
                                           @NonNull InputStream inputStream,
                                           @NonNull String fileName,
                                           @Nullable String mimeType,
                                           long totalBytes,
                                           @NonNull DownloadCallback callback) throws IOException {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            return saveViaMediaStore(activity, inputStream, fileName, mimeType, totalBytes, callback);
        } else {
            return saveViaLegacyStorage(activity, inputStream, fileName, totalBytes, callback);
        }
    }

    /**
     * Android 10+: 使用 MediaStore 保存文件
     */
    private static DownloadResult saveViaMediaStore(@NonNull Activity activity,
                                                    @NonNull InputStream inputStream,
                                                    @NonNull String fileName,
                                                    @Nullable String mimeType,
                                                    long totalBytes,
                                                    @NonNull DownloadCallback callback) throws IOException {
        ContentValues values = new ContentValues();
        values.put(MediaStore.Downloads.DISPLAY_NAME, fileName);
        values.put(MediaStore.Downloads.MIME_TYPE, mimeType != null ? mimeType : "application/octet-stream");
        values.put(MediaStore.Downloads.RELATIVE_PATH, Environment.DIRECTORY_DOWNLOADS);

        ContentResolver resolver = activity.getContentResolver();
        Uri uri = null;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            uri = resolver.insert(MediaStore.Downloads.EXTERNAL_CONTENT_URI, values);
        }
        if (uri == null) {
            throw new IOException("Failed to create MediaStore entry");
        }

        try (OutputStream out = resolver.openOutputStream(uri)) {
            if (out == null) {
                throw new IOException("Cannot open output stream for Uri: " + uri);
            }
            copyStreamWithProgress(inputStream, out, totalBytes, activity, callback);
        } catch (Exception e) {
            // 写入失败时删除已创建的条目
            resolver.delete(uri, null, null);
            throw e;
        }

        return new DownloadResult(uri, null);
    }

    /**
     * Android 10 以下: 使用传统外部存储保存文件
     */
    private static DownloadResult saveViaLegacyStorage(@NonNull Activity activity,
                                                       @NonNull InputStream inputStream,
                                                       @NonNull String fileName,
                                                       long totalBytes,
                                                       @NonNull DownloadCallback callback) throws IOException {
        if (ContextCompat.checkSelfPermission(activity, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(activity,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    REQUEST_WRITE_PERMISSION);
            throw new SecurityException("WRITE_EXTERNAL_STORAGE permission denied");
        }

        File dir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
        if (dir != null && !dir.exists()) {
            dir.mkdirs();
        }

        File file = new File(dir, fileName);
        try (FileOutputStream out = new FileOutputStream(file)) {
            copyStreamWithProgress(inputStream, out, totalBytes, activity, callback);
        }

        return new DownloadResult(Uri.fromFile(file), file);
    }

    /**
     * 复制流并报告进度
     */
    private static void copyStreamWithProgress(@NonNull InputStream in,
                                               @NonNull OutputStream out,
                                               long totalBytes,
                                               @NonNull Activity activity,
                                               @NonNull DownloadCallback callback) throws IOException {
        byte[] buffer = new byte[BUFFER_SIZE];
        long downloaded = 0;
        int bytesRead;
        long lastUpdateTime = 0;

        while ((bytesRead = in.read(buffer)) != -1) {
            out.write(buffer, 0, bytesRead);
            downloaded += bytesRead;

            // 限制进度更新频率，避免过于频繁的 UI 线程调用
            long currentTime = System.currentTimeMillis();
            if (currentTime - lastUpdateTime >= PROGRESS_UPDATE_INTERVAL) {
                final long progress = downloaded;
                activity.runOnUiThread(() -> callback.onProgress(progress, totalBytes));
                lastUpdateTime = currentTime;
            }
        }
        out.flush();

        // 确保最后一次进度更新
        final long finalProgress = downloaded;
        activity.runOnUiThread(() -> callback.onProgress(finalProgress, totalBytes));
    }
}

下载目录

兼容各个版本的文件下载目录

public static String getBaseDir(Context context) {
    String baseDir;

    // Android 10 (API 29) 及以上：使用应用专属外部存储（无需权限，自动沙盒）
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
        File externalFilesDir = context.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);
        if (externalFilesDir != null) {
            baseDir = externalFilesDir.getAbsolutePath();
        } else {
            // fallback to internal storage if external is unavailable
            baseDir = context.getFilesDir().getAbsolutePath();
        }
    } else {
        // Android 9 及以下：优先使用公共外部存储，否则用内部存储
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            baseDir = Environment.getExternalStorageDirectory().getAbsolutePath();
        } else {
            baseDir = context.getFilesDir().getAbsolutePath();
        }
    }
    File file = new File(baseDir);
    if (!file.exists()) {//判断文件目录是否存在
        file.mkdirs();
    }
    return baseDir;
}

我是码客，我是全栈工程师，我为自己代言。

Android文件下载在各个Android版本上兼容

前言

下载工具类

下载目录