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(); } }
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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：
importandroid.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(); }
