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：
- U盘权限问题
-
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"/>