Android(安卓)studio 将字符串写入本地的操作

File 类的操作：
1.首先需要添加相关权限：

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

注意6.0以上需要动态申请：

 private  void checkPermission(){        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {//6.0以上            int permission = ActivityCompat.checkSelfPermission(getApplication(), Manifest.permission.RECEIVE_SMS);            int permission1 = ActivityCompat.checkSelfPermission(getApplication(), Manifest.permission.WRITE_EXTERNAL_STORAGE);            if(permission != PackageManager.PERMISSION_GRANTED && permission1 != PackageManager.PERMISSION_GRANTED) {                Log.e(TAG,"没有获取权限，请申请");                // 申请一个（或多个）权限，并提供用于回调返回的获取码（用户定义)                if (ActivityCompat.shouldShowRequestPermissionRationale(this,                        Manifest.permission.RECEIVE_SMS) && ActivityCompat.shouldShowRequestPermissionRationale(this,                        Manifest.permission.WRITE_EXTERNAL_STORAGE)) {//这里可以写个对话框之类的项向用户解释为什么要申请权限，并在对话框的确认键后续再次申请权限                    Log.e(TAG,"提示");                    ActivityCompat.requestPermissions(this,                            new String[]{Manifest.permission.RECEIVE_SMS,Manifest.permission.WRITE_EXTERNAL_STORAGE}, CODE_READ_SMS);                } else {                    //申请权限，字符串数组内是一个或多个要申请的权限，1是申请权限结果的返回参数，在onRequestPermissionsResult可以得知申请结果                    Log.e(TAG,"您已禁止");                    Toast.makeText(MainActivity.this,"没有获取读取手机权限，请到应用中心手动打开该权限",Toast.LENGTH_SHORT).show();                }            }else{                 Log.e(TAG,"获取到了权限");            }        }else{            Log.e(TAG,"获取到了权限");        }    }    @Override    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {        super.onRequestPermissionsResult(requestCode, permissions, grantResults);        if(requestCode == CODE_READ_SMS){            if(grantResults[0] == PackageManager.PERMISSION_GRANTED) {                Log.e(TAG,"获取到了权限");            } else{                // 没有获取到权限，做特殊处理                Log.e(TAG,"没有获取到权限");                Toast.makeText(MainActivity.this,"没有获取读取手机权限，请到应用中心手动打开该权限",Toast.LENGTH_SHORT).show();            }        }    }

2.saveToFile

a)BufferedWriter 追加

//保存文件到sd卡    public void saveToFile(String content) {        BufferedWriter out = null;        //获取SD卡状态        String state = Environment.getExternalStorageState();        //判断SD卡是否就绪        if (!state.equals(Environment.MEDIA_MOUNTED)) {            Toast.makeText(this, "请检查SD卡", Toast.LENGTH_SHORT).show();            return;        }        //取得SD卡根目录        File file = Environment.getExternalStorageDirectory();        try {            Log.e(TAG, "======SD卡根目录：" + file.getCanonicalPath());            if(file.exists()){                LOG.e(TAG, "file.getCanonicalPath() == " + file.getCanonicalPath());            }            /*            输出流的构造参数1：可以是File对象  也可以是文件路径            输出流的构造参数2：默认为False=>覆盖内容； true=>追加内容             */            out = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file.getCanonicalPath() + "/readMsg.txt",true)));            out.newLine();            out.write(content);            Toast.makeText(this, "保存成功", Toast.LENGTH_SHORT).show();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (out != null) {                try {                    out.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }    }

b)FileWriter追加

 /**     * 使用FileWriter进行文本内容的追加     * @param file     * @param content     */    private void addTxtToFileWrite(File file, String content){        FileWriter writer = null;        try {            //FileWriter(file, true),第二个参数为true是追加内容，false是覆盖            writer = new FileWriter(file, true);            writer.write("\r\n");//换行            writer.write(content);        } catch (IOException e) {            e.printStackTrace();        } finally {            try {                if(writer != null){                    writer.close();                }            } catch (IOException e) {                e.printStackTrace();            }        }    }}

3.readFromFile()

 //从SD卡读取文件    public String readFromFile() {        //读的时候要用字符流   万一里面有中文        BufferedReader reader = null;        FileInputStream fis;        StringBuilder sbd = new StringBuilder();        String state = Environment.getExternalStorageState();        if (!state.equals(Environment.MEDIA_MOUNTED)) {            Toast.makeText(this, "SD卡未就绪", Toast.LENGTH_SHORT).show();            return "";        }        File root = Environment.getExternalStorageDirectory();        try {            fis = new FileInputStream(root + "/readMsg.txt");            reader = new BufferedReader(new InputStreamReader(fis));            String row;            while ((row = reader.readLine()) != null) {                sbd.append(row);            }        } catch (FileNotFoundException e) {            Toast.makeText(this, "文件不存在", Toast.LENGTH_SHORT).show();            //e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } finally {            if (reader != null) {                try {                    reader.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }        return sbd.toString();    }

4.removeFromFile()

//删除SD卡文件    public void removeFromFile() {        String state = Environment.getExternalStorageState();        if (!state.equals(Environment.MEDIA_MOUNTED)) {            Toast.makeText(this, "SD卡未就绪", Toast.LENGTH_SHORT).show();            return;        }        //取得SD卡根目录        File root = Environment.getExternalStorageDirectory();        File myFile=new File(root+"/sd.txt");        //File myFile=new File(root,"sd.txt");        if (myFile.exists()) {            myFile.delete();            Toast.makeText(this,"文件已删除",Toast.LENGTH_SHORT).show();        }else {            Toast.makeText(this,"文件不存在",Toast.LENGTH_SHORT).show();        }    }}

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