andorid写文件问题

1.权限

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

2.动态申请权限

  private static final int REQUEST_EXTERNAL_STORAGE = 1;

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

    //然后通过一个函数来申请
    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();
        }
    }

3.调用

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        verifyStoragePermissions(MainActivity.this);

}

4.写文件函数

    public static String readTxt(String txtPath) {
        File file = new File(txtPath);
        if(file.isFile() && file.exists()){
            try {
                FileInputStream fileInputStream = new FileInputStream(file);
                InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream);
                BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

                StringBuffer sb = new StringBuffer();
                String text = null;
                while((text = bufferedReader.readLine()) != null){
                    sb.append(text);
                }
                bufferedReader.close();
                return sb.toString();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public static void writeTxt(String txtPath, String content)
    {
        FileOutputStream fileOutputStream = null;
        File file = new File(txtPath);
        try
        {
            if (! file.exists())
            {
                //判断文件是否存在，如果不存在就新建一个txt
                file.createNewFile();
            }
            fileOutputStream = new FileOutputStream(file);
            fileOutputStream.write(content.getBytes());
            fileOutputStream.flush();
            fileOutputStream.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

5.使用

FileUtils_X.writeTxt(path, text);//写入唯一标识符

6.如果遇到权限问题,将这个按这个改低一点

android {
    compileSdkVersion 28
    buildToolsVersion "29.0.2"

    defaultConfig {
        applicationId "chenlong.chenlong.createtoken"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 2
        versionName "1.1"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

 

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