Android開發(fā)學(xué)習(xí)教程（30）- Android數(shù)據(jù)存儲(chǔ)的幾種方式
—— 十七歲全力以赴，十八歲好好慶祝，F(xiàn)ighting！
Android存儲(chǔ)android四大組件之一，所以它的數(shù)據(jù)存儲(chǔ)方式在介紹四大組件的時(shí)候說明。
1、文件存儲(chǔ)
文件存儲(chǔ)不對(duì)存儲(chǔ)的內(nèi)容進(jìn)行任何的格式化處理，所有數(shù)據(jù)都是原封不動(dòng)地保存到文件當(dāng)中的，因而它比較適合用于存儲(chǔ)一些簡(jiǎn)單的文本數(shù)據(jù)或二進(jìn)制數(shù)據(jù)。文件存儲(chǔ)有兩種方式，一是存儲(chǔ)到手機(jī)內(nèi)存中（memory）,一是存儲(chǔ)到sd卡中。
1.1 存儲(chǔ)到手機(jī)內(nèi)存中
Context類中提供了一個(gè) openFileOutput()方法，可以用于將數(shù)據(jù)存儲(chǔ)到指定的文件中：
??openFileOutput(name, mode):??name:是文件名，注意這里指定的文件名不可以包含路徑，因?yàn)樗械奈募际悄J(rèn)存儲(chǔ)到/data/data/<package?name="">/files/(等價(jià)于 getFilesDir())目 錄下 的??mode:是文件的操作模式 ，MODE_PRIVATE：默認(rèn)的操作模式，同名文件內(nèi)容會(huì)被覆蓋。MODE_APPEND則表示 如果該文件已存在就往文件里面追加內(nèi)容，不存在就創(chuàng)建新文件。</package>public?void?save(String data) {????FileOutputStream out =?null;????BufferedWriter writer =?null;????try?{????????out = openFileOutput("content", Context.MODE_PRIVATE);????????writer =?new?BufferedWriter(new?OutputStreamWriter(out));????????writer.write(data);????}?catch?(IOException e) {????????e.printStackTrace();????}?finally?{????????try?{????????????if?(writer !=?null) {????????????????writer.close();????????????}????????}?catch?(IOException e) {????????}????}}public?String read() {????FileInputStream in =?null;????BufferedReader reader =?null;????StringBuilder content =?new?StringBuilder();????try?{????????in = openFileInput("content");????????reader =?new?BufferedReader(new?InputStreamReader(in));????????String line =?"";????????while?((line = reader.readLine()) !=?null) {????????????content.append(line);????????}????}?catch?(IOException e) {????????e.printStackTrace();????}?finally?{????????if?(reader !=?null) {????????????try?{????????????????reader.close();????????????}?catch?(IOException e) {????????????????e.printStackTrace();????????????}????????}????}????return?content.toString();}1.2 存儲(chǔ)到手機(jī)SD卡中
前面說的存儲(chǔ)到手機(jī)內(nèi)存，數(shù)據(jù)是存儲(chǔ)在應(yīng)用程序內(nèi)的，文件大小受到限制，而且數(shù)據(jù)隨著程序的卸載而自動(dòng)清除；當(dāng)要存儲(chǔ)大的文件時(shí)，或者想數(shù)據(jù)不會(huì)隨著程序的卸載而自動(dòng)清除就可以使用sd卡方式存儲(chǔ)了。使用sd卡存儲(chǔ)主要是使用Environment這個(gè)類的功能。
注：在Android6.0之后讀寫SD卡等危險(xiǎn)的操作需要?jiǎng)討B(tài)申請(qǐng)存儲(chǔ)等權(quán)限。否則可能會(huì)報(bào)異常java.io.FileNotFoundException: /storage/emulated/0/test: open failed: EACCES (Permission denied)
第 1 步：在AndroidManifest清掉中添加所需權(quán)限
????<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE">????<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission></uses-permission>第 2 步：動(dòng)態(tài)申請(qǐng)權(quán)限
requestPermissions(new?String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE},?101);第 3 步：使用Environment獲取SD目錄，讀寫數(shù)據(jù)：
public?void?save(String data) {????try?{????????// 獲取SDcard路徑????????File sdCardDir = Environment.getExternalStorageDirectory();????????// SDCard目錄：/mnt/sdcard????????String sdcardPath = sdCardDir.getAbsolutePath();????????File file =?new?File(sdCardDir,?"test");????????RandomAccessFile raf =?new?RandomAccessFile(file,?"rw");????????// 將文件記錄指針移動(dòng)最后????????raf.seek(file.length());????????// 輸出文件內(nèi)容????????raf.write(data.getBytes());????????raf.close();????}?catch?(Exception e) {????????e.printStackTrace();????}}public?String read() {????StringBuilder sb =?new?StringBuilder();????// 獲取SDcard路徑????try?{????????File sdCardDir = Environment.getExternalStorageDirectory();????????File file =?new?File(sdCardDir,?"test");????????InputStream inputStream =?new?FileInputStream(file);????????int?len =?0;????????byte[] buffer =?new?byte[1024];????????while?((len = inputStream.read(buffer)) != -1) {????????????sb.append(new?String(buffer,?0, len));????????}????????// 關(guān)閉流????????inputStream.close();????}?catch?(Exception e) {????????e.printStackTrace();????}????return?sb.toString();}2、SharedPreferences存儲(chǔ)
SharedPreferences類，它是一個(gè)輕量級(jí)的存儲(chǔ)類，適合用于保存軟件配置參數(shù)。SharedPreferences是使用鍵值對(duì)的方式來存儲(chǔ)數(shù)據(jù)的，存儲(chǔ)數(shù)據(jù)是以xml文件形式存儲(chǔ)，文件存放在/data/data/your package name/shared_prefs目錄下。
public?void?save(String data) {????SharedPreferences preferences = getSharedPreferences("test", MODE_APPEND);????SharedPreferences.Editor editor = preferences.edit();????editor.putString("content", data);????editor.commit();}public?String read() {????SharedPreferences preferences = getSharedPreferences("test", MODE_PRIVATE);????return?preferences.getString("content",?"");}源碼鏈接：https://yunjunet.cn/876833.html
