android6版本以上的需要动态获取权限

private static String[] PERMISSIONS_STORAGE = {
        "android.permission.READ_EXTERNAL_STORAGE",
        "android.permission.WRITE_EXTERNAL_STORAGE"};

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //动态获取权限
    verifyStoragePermissions(this);
}

//动态获取权限
private void verifyStoragePermissions(Activity activity) {
    int permission = ActivityCompat.checkSelfPermission(activity, PERMISSIONS_STORAGE[0]);
    if (permission != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(activity, PERMISSIONS_STORAGE, 1);
    }
}

然后在manifest中加上：

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

android 10中文件读写新特性。还需要在Androidmanifast的application节点中加入android:requestLegacyExternalStorage="true"