重点关于android 12的sd卡读写以及Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)的使用

首先要有对sd卡读写的权限 android 12 申请权限大全

<uses-permission android:name="android.permission.INTERNET" /> <!-- 网络权限 -->
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="android.permission.DISABLE_KEYGUARD" /> <!-- 读取外置存储。如果开发者使用了so动态加载功能并且把so文件放在了外置存储区域，则需要申请该权限，否则不需要 -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> <!-- 允许访问SD卡的权限 -->
    <!-- 写外置存储。如果开发者使用了离线地图，并且数据写在外置存储区域，则需要申请该权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission
        android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
        tools:ignore="ProtectedPermissions" /> <!-- 获取网络状态，根据网络状态切换进行数据请求网络转换 -->
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <!-- 读取网络状态 -->
    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />
    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

然后需要在AndroidManifest.xml文件中<application 加入
android:requestLegacyExternalStorage=“true”

其次在activity中动态申请权限

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        

if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            // Permission is not granted, request it
            int MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE = 1;
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                    MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);
        } else {
            // Permission has already been granted, read the file
            video   = ImageSaverUtil.readImageFromSDCard("video");
        }

  
    }

package com.example.zhuoyuadvert.utils;

import static org.greenrobot.eventbus.EventBus.TAG;

import android.content.Context;
import android.os.Build;
import android.os.Environment;
import android.util.Log;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.ReentrantLock;

public class ImageSaverUtil {
    private static ReentrantLock lock = new ReentrantLock(); 
    // 写入sd卡需要保证线程使用
    public static void saveImageToInternalStorage(Context context, List<String> imageUrl, String folderName, String name) {
        new Thread(() -> {
            lock.lock();
            String savedImagePath = null;
            if (Build.VERSION.SDK_INT >= 29) {
                File folder = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), folderName);
                if (!folder.exists()) {
                    folder.mkdirs();
                } else {
                    deleteFiles(folder);
                }
                for (int i = 0; i < imageUrl.size(); i++) {
                    try {
                        // Get the input stream from the URL
                        InputStream inputStream = new URL(imageUrl.get(i)).openStream();
                        // Create a request to save the image to the app's internal storage
                        File imageFile = new File(folder, folderName + System.currentTimeMillis() + name);
                        OutputStream outputStream = new FileOutputStream(imageFile);

                        // Copy the image from the input stream to the output stream
                        byte[] buffer = new byte[1024];
                        int bytesRead;
                        while ((bytesRead = inputStream.read(buffer)) != -1) {
                            outputStream.write(buffer, 0, bytesRead);
                        }

                        // Close the streams
                        outputStream.close();
                        inputStream.close();

                        savedImagePath = imageFile.getAbsolutePath();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
                // Use the Scoped Storage APIs on Android 12 and higher
                Log.d("ImageSaver", "Saved image to path: " + savedImagePath);
            }
           lock.unlock();

        }).start();
          
    }

	//每次写入前有需要可以先把文件清空
    private static boolean deleteFiles(File file) {
        try {
            if (file.isDirectory()) { //判断是否是文件夹
                File[] files = file.listFiles();//遍历文件夹里面的所有的
                for (int i = 0; i < files.length; i++) {
                    Log.e(TAG, "删除文件>>>>>> " + files[i].toString());
                    deleteFiles(files[i]); //删除
                }
            } else {
                boolean delete = file.delete();
                System.out.println(delete);
            }
            System.gc();//系统回收垃圾
            return true;
        } catch (Exception e) {
            Log.e(TAG, "删除报错！！！: " + e.toString());
            return false;

        }

    }
	//读取sd卡内容
    public static List<String> readImageFromSDCard( String folderName) {


        List<String> bitmaps = new ArrayList<>();
        try {
            // Get  path
            // Create a request to save the image to the app's internal storage
            File folder = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), folderName);
            File[] files = folder.listFiles();
            List<String> imagePaths = new ArrayList<>();
            if (files != null) {
                for (int i = 0; i < files.length; i++) {
                    imagePaths.add(files[i].getPath());
                    File imageFile = new File(files[i].getPath());
                    //Bitmap image = BitmapFactory.decodeFile(imageFile.getAbsolutePath());
                    bitmaps.add(imageFile.getAbsolutePath());
                }
            }
            return bitmaps;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
}