Android文件读写

1.assets

assets文件在main文件夹中与java、res同级，assets的文件不会在R资源中生成id，目录中可以有子文件夹，文件不会被编译成二进制，存放到这里的资源在运行打包的时候都会打入程序安装包中。读取方法如下：

try {                    InputStream is = getResources().getAssets().open("info.txt");                    InputStreamReader isr = new InputStreamReader(is,"UTF-8");                    BufferedReader br = new BufferedReader(isr);//                    Log.i(TAG,br.readLine());                    String in = "";                    while ((in = br.readLine()) != null){//                        Log.i(TAG,in);                        System.out.println(in);                    }                } catch (IOException e) {                    e.printStackTrace();                }

2.raw

raw文件夹在res目录中，不能有子文件夹，会在R资源中生成id，不会被编译成二进制，这些资源在打包时只打包使用过的资源到安装包中。读取如下：

try {                    InputStream is = getResources().openRawResource(R.raw.info);                    InputStreamReader isr = new InputStreamReader(is, "UTF-8");                    BufferedReader br = new BufferedReader(isr);                    String in = "";                    while ((in = br.readLine()) != null) {//                        Log.i(TAG, in);                        System.out.println(in);                    }                } catch (IOException e) {                    e.printStackTrace();                }

3.android内部储存文件数据

android系统中会在data/data/app包名的文件夹中存储应用数据。例如我们将EditText输入的数据储存在其中：

try {    FileOutputStream fos = openFileOutput(fileName, Context.MODE_PRIVATE);    /**     * Context.MODE_PRIVATE     * 默认操作模式，代表该文件是私有数据，只能被应用本身访问，在该模式下，     * 写入的内容会覆盖原文件的内容     *     * Context.MODE_APPEND     * 检查文件是否存在，存在就往文件追加内容，否则就创建新文件。     *     */    OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8");    osw.write(editText.getText().toString());    osw.flush();    fos.flush();    osw.close();    fos.close();    Toast.makeText(getApplicationContext(), "写入完成", Toast.LENGTH_SHORT).show();} catch (IOException e) {    e.printStackTrace();}

读取时：

try {    FileInputStream fis = openFileInput(fileName);    InputStreamReader isr = new InputStreamReader(fis,"UTF-8");    char input[] = new char[fis.available()];    isr.read(input);    isr.close();    fis.close();    String readed = new String(input);    tvShow.setText(readed);} catch (IOException e) {    e.printStackTrace();}

4.android外部储存

比较常用的存储方式，同样我们将EditText输入的内容以文件的形式存储的手机中：

 File sdCard = Environment.getExternalStorageDirectory();                File myFile = new File(sdCard,"This is my file.txt");                if (sdCard.exists()){                    try {                        myFile.createNewFile();//                        System.out.println(myFile.getAbsolutePath());                        Toast.makeText(getApplicationContext(),"文件创建完成",Toast.LENGTH_SHORT).show();                        FileOutputStream fos = new FileOutputStream(myFile);                        OutputStreamWriter osw = new OutputStreamWriter(fos,"UTF-8");                        osw.write(editText.getText().toString());                        osw.flush();                        osw.close();                        fos.close();                        Toast.makeText(getApplicationContext(),"文件写入完成",Toast.LENGTH_SHORT).show();                    } catch (IOException e) {                        e.printStackTrace();                    }                } else {                    Toast.makeText(getApplicationContext(),"当前系统不具备SD卡目录",Toast.LENGTH_SHORT).show();                }

读取内容：

File myFile = new File(sdCard,"This is my file.txt");if (myFile.exists()){    try {        FileInputStream fis = new FileInputStream(myFile);        InputStreamReader isr = new InputStreamReader(fis,"UTF-8");        char input[] = new char[fis.available()];        isr.read(input);        isr.close();        fis.close();        String in = new String(input);        tvShow.setText(in);    } catch (IOException e) {        e.printStackTrace();    }}

----------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------

5.SharedPreferences（题外）

sharedpreferences是一种简单的数据储存方式，将数据以键值对存储在/data/data/包名/shared_prefs下的xml文件中。使用如下：

public class MainActivity extends AppCompatActivity {    private EditText editText;    SharedPreferences preferences;    SharedPreferences.Editor editor;    static final String KEY = "MyValue";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        preferences = getPreferences(Activity.MODE_PRIVATE);        editor = preferences.edit();        editText = (EditText) findViewById(R.id.editText);        findViewById(R.id.btnWrite).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                editor.putString(KEY, editText.getText().toString());                if (editor.commit()) {                    Toast.makeText(getApplicationContext(), "写入成功", Toast.LENGTH_SHORT).show();                }            }        });        findViewById(R.id.btnRead).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                String in = preferences.getString(KEY, "当前数值不存在");//getString(String key,String defValue)  String defValue  如果key对应的值不存在，则传入defValue                Toast.makeText(getApplicationContext(), in, Toast.LENGTH_SHORT).show();            }        });    }}

sharedpreferences还可以用在应用的首选项上：

import android.os.Bundle;import android.preference.CheckBoxPreference;import android.preference.EditTextPreference;import android.preference.ListPreference;import android.preference.PreferenceActivity;import android.preference.PreferenceManager;import android.widget.Toast;public class MyPreferenceActivity extends PreferenceActivity {//    CheckBoxPreference//    ListPreference//    EditTextPreference    PreferenceManager manager;    CheckBoxPreference checkBoxPreference;    ListPreference listPreference;    EditTextPreference editTextPreference;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        addPreferencesFromResource(R.xml.mypreference);        manager = getPreferenceManager();        checkBoxPreference = (CheckBoxPreference) manager.findPreference("checkbox");        Toast.makeText(getApplicationContext(), "当前的状态为：" + checkBoxPreference.isChecked(), Toast.LENGTH_SHORT).show();        listPreference = (ListPreference) manager.findPreference("list");        Toast.makeText(getApplicationContext(), listPreference.getEntry() + "的开发环境：" + listPreference.getValue(), Toast.LENGTH_SHORT).show();        editTextPreference = (EditTextPreference) manager.findPreference("text");        Toast.makeText(getApplicationContext(), "您输入的内容为：" + editTextPreference.getText(), Toast.LENGTH_SHORT).show();    }}

R.xml.mypreference是放在res目录中的xml文件夹中的mypreference.xml，内容如下：

<?xml version="1.0" encoding="utf-8"?><PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">    <CheckBoxPreference        android:key="checkbox"        android:summaryOff="已经关闭"        android:summaryOn="已经开启"        android:title="是否开启" />    <ListPreference        android:entries="@array/entries"        android:entryValues="@array/values"        android:key="list"        android:summary="请点击选择"        android:title="选择一个选项" />    <EditTextPreference        android:dialogMessage="有劳了"        android:dialogTitle="请输入你的名字"        android:key="text"        android:summary="请再次输入"        android:title="请输入" /></PreferenceScreen>

ListPreference的resources内容如下：

<?xml version="1.0" encoding="utf-8"?><resources>    <string-array name="entries">        <item>Java</item>        <item>Swift</item>        <item>C#</item>    </string-array>    <string-array name="values">        <item>Eclipse</item>        <item>Xcode</item>        <item>Visual Studio</item>    </string-array></resources>

6.xml数据的读写

在assets文件夹中有一份xml文件，如下：

<?xml version="1.0" encoding="utf-8"?><Languages cat="it">    <lan id="1">        <name>Java</name>        <ide>Eclipse</ide>    </lan>    <lan id="2">        <name>Swift</name>        <ide>Xcode</ide>    </lan>    <lan id="3">        <name>C#</name>        <ide>Visual Studio</ide>    </lan></Languages>

除了各种开源库外，Android 有自己的API来解析xml文件，如下：

TextView textView = (TextView) findViewById(R.id.tv);//读取xml文件try {    DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();    DocumentBuilder builder = builderFactory.newDocumentBuilder();    Document document = builder.parse(getAssets().open("languages.xml"));    Element element = document.getDocumentElement();    NodeList list = element.getElementsByTagName("lan");    for (int i = 0; i < list.getLength(); i++) {        Element lan = (Element) list.item(i);        textView.append(lan.getAttribute("id")+"\n");        textView.append(lan.getElementsByTagName("name").item(0).getTextContent()+"\n");        textView.append(lan.getElementsByTagName("ide").item(0).getTextContent()+"\n");    }} catch (IOException | ParserConfigurationException | SAXException e) {    e.printStackTrace();}//写入xml文件try {    DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();    DocumentBuilder builder = builderFactory.newDocumentBuilder();    Document documentXML = builder.newDocument();    Element element = documentXML.createElement("country");    element.setAttribute("cat", "it");    //添加里面    //第一个    Element coun1 = documentXML.createElement("coun");    coun1.setAttribute("id", "1");    Element name1 = documentXML.createElement("name");    name1.setTextContent("China");    Element lan1 = documentXML.createElement("language");    lan1.setTextContent("Chinese");    coun1.appendChild(name1);    coun1.appendChild(lan1);    element.appendChild(coun1);    //第二个    Element coun2 = documentXML.createElement("coun");    coun2.setAttribute("id", "2");    Element name2 = documentXML.createElement("name");    name2.setTextContent("America");    Element lan2 = documentXML.createElement("language");    lan2.setTextContent("English");    coun2.appendChild(name2);    coun2.appendChild(lan2);    element.appendChild(coun2);    //    documentXML.appendChild(element);    TransformerFactory transformerFactory = TransformerFactory.newInstance();    Transformer transformer = transformerFactory.newTransformer();    transformer.setOutputProperty("encoding", "UTF-8");    StringWriter sw = new StringWriter();    transformer.transform(new DOMSource(documentXML),new StreamResult(sw));    textView.setText(sw.toString());} catch (ParserConfigurationException | TransformerException e) {    e.printStackTrace();}

7.Json数据读取

同样解析assets文件夹下的json文件，需要要Gson之类的解析库，直接利用Android API，JSONObject  json  =  new JSONObject（传入json的Sting内容），具体如下：

json文件：

{  "language":[    {"id":1,"ide":"Eclipse","name":"Java"},    {"id":2,"ide":"Xcode","name":"Swift"},    {"id":3,"ide":"Visual Studio","name":"C#"}  ],  "cat":"it"}

解析：

//读取数据try {    InputStreamReader isr = new InputStreamReader(getAssets().open("test.json"), "UTF-8");    BufferedReader br = new BufferedReader(isr);    String line;    StringBuilder builder = new StringBuilder();    while ((line = br.readLine()) != null) {        builder.append(line);    }    br.close();    isr.close();    JSONObject root = new JSONObject(builder.toString());    System.out.println("cat = " + root.getString("cat"));    JSONArray array = root.getJSONArray("language");    for (int i=0;i<array.length();i++){        JSONObject lan = array.getJSONObject(i);        System.out.println("---------------------------------");        System.out.println("id = " + lan.getInt("id"));        System.out.println("ide = " + lan.getString("ide"));        System.out.println("name = " + lan.getString("name"));    }} catch (IOException | JSONException e) {    e.printStackTrace();}//写入数据try {    JSONObject root = new JSONObject();    root.put("cat","it");    //创建单个对象 {"id":1,"ide":"Eclipse","name":"Java"}    JSONObject lan1 = new JSONObject();    lan1.put("id",1);    lan1.put("ide","Eclipse");    lan1.put("name","Java");    //{"id":2,"ide":"Xcode","name":"Swift"}    JSONObject lan2 = new JSONObject();    lan2.put("id",2);    lan2.put("ide","Xcode");    lan2.put("name","Swift");    //{"id":3,"ide":"Visual Studio","name":"C#"}    JSONObject lan3 = new JSONObject();    lan3.put("id",3);    lan3.put("ide","Visual Studio");    lan3.put("name","C#");    //JSON数据添加单个对象    JSONArray array = new JSONArray();    array.put(lan1);    array.put(lan2);    array.put(lan3);    root.put("langusges",array);    System.out.println(root.toString());} catch (JSONException e) {    e.printStackTrace();}