Android SD卡

//动态申请权限方法
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {
        "android.permission.READ_EXTERNAL_STORAGE",
        "android.permission.WRITE_EXTERNAL_STORAGE" };
public static void verifyStoragePermissions(Activity activity) {
    try {
        //检测是否有写的权限
        int permission = ActivityCompat.checkSelfPermission(activity,
                "android.permission.WRITE_EXTERNAL_STORAGE");
        if (permission != PackageManager.PERMISSION_GRANTED) {
            // 没有写的权限，去申请写的权限，会弹出对话框
            ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE,REQUEST_EXTERNAL_STORAGE);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

File f2=new File(ext,"test.data");
try {
    verifyStoragePermissions(MainActivity.this);
    OutputStream out=new FileOutputStream(f2);
    out.write("test".getBytes());
    out.close();
} catch (Exception e) {
    e.printStackTrace();
}

try {
    InputStream in=new FileInputStream(f2);
    byte[] buffer=new byte[64];
    int len=in.read(buffer);
    String str=new String(buffer,0,len);
} catch (Exception e) {
    e.printStackTrace();
}