Android设备与外接U盘实现数据读取操作

现在越来越多手机支持OTG功能，通过OTG可以实现与外接入的U盘等USB设备实现数据传输。关于OTG，可以参考：
http://blog.csdn.net/srw11/article/details/39154053。
最近项目上用到了该功能，项目上用的是安卓7.1的盒子，要实现与插入的U盘进行数据操作。通过大量的找资料，终于实现了项目上需要的功能。找资料主要是解决两个问题：

1. U盘权限问题

2. U盘文件路径及文件操作

   废话不多说，感觉还是喜欢直接上代码才爽快。项目中用到了一个开源框架，开源地址是： 
   https://github.com/magnusja/libaums。

---

代码部分：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    //输入的内容
    private EditText u_disk_edt;
    //写入到U盘
    private Button u_disk_write;
    //从U盘读取
    private Button u_disk_read;
    //显示读取的内容
    private TextView u_disk_show;
    //自定义U盘读写权限
    private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
    //当前处接U盘列表
    private UsbMassStorageDevice[] storageDevices;
    //当前U盘所在文件目录
    private UsbFile cFolder;
    private final static String U_DISK_FILE_NAME = "u_disk.txt";
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case 100:
                    showToastMsg("保存成功");
                    break;
                case 101:
                    String txt = msg.obj.toString();
                    if (!TextUtils.isEmpty(txt))
                        u_disk_show.setText("读取到的数据是：" + txt);
                    break;
            }
        }
    };

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

    private void initViews() {
        u_disk_edt = (EditText) findViewById(R.id.u_disk_edt);
        u_disk_write = (Button) findViewById(R.id.u_disk_write);
        u_disk_read = (Button) findViewById(R.id.u_disk_read);
        u_disk_show = (TextView) findViewById(R.id.u_disk_show);
        u_disk_write.setOnClickListener(this);
        u_disk_read.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.u_disk_write:
                final String content = u_disk_edt.getText().toString().trim();
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        saveText2UDisk(content);
                    }
                });

                break;
            case R.id.u_disk_read:
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        readFromUDisk();
                    }
                });

                break;
        }
    }

    private void readFromUDisk() {
        UsbFile[] usbFiles = new UsbFile[0];
        try {
            usbFiles = cFolder.listFiles();
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (null != usbFiles && usbFiles.length > 0) {
            for (UsbFile usbFile : usbFiles) {
                if (usbFile.getName().equals(U_DISK_FILE_NAME)) {
                    readTxtFromUDisk(usbFile);
                }
            }
        }
    }

    /**
     * @description 保存数据到U盘，目前是保存到根目录的
     * @author ldm
     * @time 2017/9/1 17:17
     */
    private void saveText2UDisk(String content) {
        //项目中也把文件保存在了SD卡，其实可以直接把文本读取到U盘指定文件
        File file = FileUtil.getSaveFile(getPackageName()
                        + File.separator + FileUtil.DEFAULT_BIN_DIR,
                U_DISK_FILE_NAME);
        try {
            FileWriter fw = new FileWriter(file);
            fw.write(content);
            fw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (null != cFolder) {
            FileUtil.saveSDFile2OTG(file, cFolder);
            mHandler.sendEmptyMessage(100);
        }
    }

    /**
     * @description OTG广播注册
     * @author ldm
     * @time 2017/9/1 17:19
     */
    private void registerUDiskReceiver() {
        //监听otg插入 拔出
        IntentFilter usbDeviceStateFilter = new IntentFilter();
        usbDeviceStateFilter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
        usbDeviceStateFilter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
        registerReceiver(mOtgReceiver, usbDeviceStateFilter);
        //注册监听自定义广播
        IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
        registerReceiver(mOtgReceiver, filter);
    }

    /**
     * @description OTG广播，监听U盘的插入及拔出
     * @author ldm
     * @time 2017/9/1 17:20
     * @param
     */
    private BroadcastReceiver mOtgReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            switch (action) {
                case ACTION_USB_PERMISSION://接受到自定义广播
                    UsbDevice usbDevice = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    //允许权限申请
                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if (usbDevice != null) {
                            //用户已授权，可以进行读取操作
                            readDevice(getUsbMass(usbDevice));
                        } else {
                            showToastMsg("没有插入U盘");
                        }
                    } else {
                        showToastMsg("未获取到U盘权限");
                    }
                    break;
                case UsbManager.ACTION_USB_DEVICE_ATTACHED://接收到U盘设备插入广播
                    UsbDevice device_add = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                    if (device_add != null) {
                        //接收到U盘插入广播，尝试读取U盘设备数据
                        redUDiskDevsList();
                    }
                    break;
                case UsbManager.ACTION_USB_DEVICE_DETACHED://接收到U盘设设备拔出广播
                    showToastMsg("U盘已拔出");
                    break;
            }
        }
    };

    /**
     * @description U盘设备读取
     * @author ldm
     * @time 2017/9/1 17:20
     */
    private void redUDiskDevsList() {
        //设备管理器
        UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
        //获取U盘存储设备
        storageDevices = UsbMassStorageDevice.getMassStorageDevices(this);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
        //一般手机只有1个OTG插口
        for (UsbMassStorageDevice device : storageDevices) {
            //读取设备是否有权限
            if (usbManager.hasPermission(device.getUsbDevice())) {
                readDevice(device);
            } else {
                //没有权限，进行申请
                usbManager.requestPermission(device.getUsbDevice(), pendingIntent);
            }
        }
        if (storageDevices.length == 0) {
            showToastMsg("请插入可用的U盘");
        }
    }

    private UsbMassStorageDevice getUsbMass(UsbDevice usbDevice) {
        for (UsbMassStorageDevice device : storageDevices) {
            if (usbDevice.equals(device.getUsbDevice())) {
                return device;
            }
        }
        return null;
    }

    private void readDevice(UsbMassStorageDevice device) {
        try {
            device.init();//初始化
            //设备分区
            Partition partition = device.getPartitions().get(0);
            //文件系统
            FileSystem currentFs = partition.getFileSystem();
            currentFs.getVolumeLabel();//可以获取到设备的标识
            //通过FileSystem可以获取当前U盘的一些存储信息，包括剩余空间大小，容量等等
            Log.e("Capacity: ", currentFs.getCapacity() + "");
            Log.e("Occupied Space: ", currentFs.getOccupiedSpace() + "");
            Log.e("Free Space: ", currentFs.getFreeSpace() + "");
            Log.e("Chunk size: ", currentFs.getChunkSize() + "");
            cFolder = currentFs.getRootDirectory();//设置当前文件对象为根目录
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void showToastMsg(String msg) {
        Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
    }

    private void readTxtFromUDisk(UsbFile usbFile) {
        UsbFile descFile = usbFile;
        //读取文件内容
        InputStream is = new UsbFileInputStream(descFile);
        //读取秘钥中的数据进行匹配
        StringBuilder sb = new StringBuilder();
        BufferedReader bufferedReader = null;
        try {
            bufferedReader = new BufferedReader(new InputStreamReader(is));
            String read;
            while ((read = bufferedReader.readLine()) != null) {
                sb.append(read);
            }
            Message msg = mHandler.obtainMessage();
            msg.what = 101;
            msg.obj = read;
            mHandler.sendMessage(msg);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (bufferedReader != null) {
                    bufferedReader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

对应布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.ldm.androidudisk.MainActivity"
        android:orientation="vertical">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Android盒子外接U盘文件读写测试DEMO"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            />

    <EditText
            android:id="@+id/u_disk_edt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:hint="输入要保存到U盘中的文字内容"/>


    <Button
            android:id="@+id/u_disk_write"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:gravity="center"
            android:text="往U盘中写入数据"/>

    <Button
            android:id="@+id/u_disk_read"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:gravity="center"
            android:text="从U盘中读取数据"/>

    <TextView
            android:id="@+id/u_disk_show"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginLeft="10dp"
            />
</LinearLayout>

文件操作工具类：

package com.ldm.androidudisk.utils;

import android.os.Environment;

import com.github.mjdev.libaums.fs.UsbFile;
import com.github.mjdev.libaums.fs.UsbFileOutputStream;

import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import static android.os.Environment.getExternalStorageDirectory;

/**
 * 文件操作工具类
 *
 * @author ldm
 * @description：
 * @date 2016-4-28 下午3:17:10
 */
public final class FileUtil {
    public static final String DEFAULT_BIN_DIR = "usb";

    /**
     * 检测SD卡是否存在
     */
    public static boolean checkSDcard() {
        return Environment.MEDIA_MOUNTED.equals(Environment
                .getExternalStorageState());
    }

    /**
     * 从指定文件夹获取文件
     *
     * @return 如果文件不存在则创建, 如果如果无法创建文件或文件名为空则返回null
     */
    public static File getSaveFile(String folderPath, String fileNmae) {
        File file = new File(getSavePath(folderPath) + File.separator
                + fileNmae);
        try {
            file.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return file;
    }

    /**
     * 获取SD卡下指定文件夹的绝对路径
     *
     * @return 返回SD卡下的指定文件夹的绝对路径
     */
    public static String getSavePath(String folderName) {
        return getSaveFolder(folderName).getAbsolutePath();
    }

    /**
     * 获取文件夹对象
     *
     * @return 返回SD卡下的指定文件夹对象，若文件夹不存在则创建
     */
    public static File getSaveFolder(String folderName) {
        File file = new File(getExternalStorageDirectory()
                .getAbsoluteFile()
                + File.separator
                + folderName
                + File.separator);
        file.mkdirs();
        return file;
    }

    /**
     * 关闭流
     */
    public static void closeIO(Closeable... closeables) {
        if (null == closeables || closeables.length <= 0) {
            return;
        }
        for (Closeable cb : closeables) {
            try {
                if (null == cb) {
                    continue;
                }
                cb.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private static void redFileStream(OutputStream os, InputStream is) throws IOException {
        int bytesRead = 0;
        byte[] buffer = new byte[1024 * 8];
        while ((bytesRead = is.read(buffer)) != -1) {
            os.write(buffer, 0, bytesRead);
        }
        os.flush();
        os.close();
        is.close();
    }

    /**
     * @description 把本地文件写入到U盘中
     * @author ldm
     * @time 2017/8/22 10:22
     */
    public static void saveSDFile2OTG(final File f, final UsbFile usbFile) {
        UsbFile uFile = null;
        FileInputStream fis = null;
        try {//开始写入
            fis = new FileInputStream(f);//读取选择的文件的
            if (usbFile.isDirectory()) {//如果选择是个文件夹
                UsbFile[] usbFiles = usbFile.listFiles();
                if (usbFiles != null && usbFiles.length > 0) {
                    for (UsbFile file : usbFiles) {
                        if (file.getName().equals(f.getName())) {
                            file.delete();
                        }
                    }
                }
                uFile = usbFile.createFile(f.getName());
                UsbFileOutputStream uos = new UsbFileOutputStream(uFile);
                try {
                    redFileStream(uos, fis);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (final Exception e) {
            e.printStackTrace();
        }
    }
}

不要忘记在app/build.grade下添加：

compile 'com.github.mjdev:libaums:0.5.5'

及AndroidManifest.xml中添加权限：

  <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>