AndroidManifest.xml ↓

 <!--加读写权限-->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

Java ↓

	//定义请求码
    private static final int REQUEST_EXTERNAL_STORAGE = 1;
    private static String[] PERMISSIONS = {
            "android.permission.READ_EXTERNAL_STORAGE",
            "android.permission.WRITE_EXTERNAL_STORAGE" };

    //然后通过一个函数来申请
    public static void readWritePermission(Activity activity) {
        try {
            //检测是否有权限：permission = 0 ，则有权限
            int permission = ActivityCompat.checkSelfPermission(activity,
                    "android.permission.WRITE_EXTERNAL_STORAGE");
            //判断是否有权限，没有则弹出对话框
            if (permission != PackageManager.PERMISSION_GRANTED) {
                //Activity的实例、String数组、请求码
                ActivityCompat.requestPermissions(activity, PERMISSIONS,REQUEST_EXTERNAL_STORAGE);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }



//--------------在 onCreate中调用此函数--------------
readWritePermission(this);

效果图 ↓