android数据存储之文件存储

package com.android.saveData;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import android.app.Activity;import android.content.Context;import android.os.Bundle;import android.os.Environment;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class FileSaveDataActivity extends Activity implements OnClickListener {    private EditText mEditText;private Button mSaveToFileButton;private Button mReadFromFileButton;private Button mSaveToSDButton;private Button mReadFromSDButton;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                initView();                addListener();    }        private void initView() {    mEditText = (EditText)findViewById(R.id.mEditText_id);    mSaveToFileButton = (Button)findViewById(R.id.saveToFile_id);    mReadFromFileButton = (Button)findViewById(R.id.readFromFile_id);    mSaveToSDButton = (Button)findViewById(R.id.saveToSD_id);    mReadFromSDButton = (Button)findViewById(R.id.readFromSD_id);    }        private void addListener() {    mSaveToFileButton.setOnClickListener(this);    mReadFromFileButton.setOnClickListener(this);    mSaveToSDButton.setOnClickListener(this);    mReadFromSDButton.setOnClickListener(this);    }@Overridepublic void onClick(View view) {String fileName = "fileSave.txt";switch(view.getId()) {case R.id.readFromFile_id:try {FileInputStream inStream = getApplicationContext().openFileInput(fileName);ByteArrayOutputStream mStream = new ByteArrayOutputStream();byte[] buffer = new byte[1024];int length = -1;while((length = inStream.read(buffer)) != -1) {mStream.write(buffer, 0, length);}Toast.makeText(getApplicationContext(), new String(buffer), Toast.LENGTH_LONG).show();mStream.close();inStream.close();} catch (FileNotFoundException e1) {// TODO Auto-generated catch blocke1.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}break;case R.id.readFromSD_id:if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {File sdCardDir = Environment.getExternalStorageDirectory();File readFile = new File(sdCardDir, fileName);try {FileInputStream inStream = new FileInputStream(readFile);ByteArrayOutputStream mStream = new ByteArrayOutputStream();byte[] buffer = new byte[1024];int length = -1;while((length = inStream.read(buffer)) != -1) {mStream.write(buffer, 0, length);}Toast.makeText(getApplicationContext(), new String(buffer), Toast.LENGTH_LONG).show();mStream.close();inStream.close();} catch (FileNotFoundException e1) {// TODO Auto-generated catch blocke1.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}break;case R.id.saveToFile_id:try {FileOutputStream outStream = getApplicationContext().openFileOutput(fileName, Context.MODE_WORLD_READABLE);outStream.write(mEditText.getText().toString().getBytes());outStream.close();} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}break;case R.id.saveToSD_id:if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {File sdCardDir = Environment.getExternalStorageDirectory();File saveFile = new File(sdCardDir, fileName);try {FileOutputStream outStream = new FileOutputStream(saveFile);outStream.write(mEditText.getText().toString().getBytes());outStream.close();} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}break;default:break;}}}

添加权限：

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

openFileOutput(fileName, Context.MODE_WORLD_READABLE)

方法，fileName不包含路径分隔符"/",如果文件不存在，android会自动创建，且保存在/data/data/<package name>/files目录，

Context.MODE_PRIVATE：该文件时私有数据，只能在应用本身访问，写入的内容会覆盖原文件，如想把新写入的内容追加到原文件，就用Context.MODE_APPEND

Context.MODE_APPEND：先检查文件是否存在，不存在就新建，存在就追加

下面两个是设置其他应用是否有权限读取这个数据:

Context.MODE_WORLD_WRITEABLE：读取数据

Context.MODE_WORLD_READABLE：写入数据

如果要其他应用要读和写权限的 可以：

openFileOutput(fileName, Context.MODE_WORLD_READABLE + Context.MODE_WORLD_WRITEABLE)

Activity还提供了getCacheDir()和getFilesDir()方法：
getCacheDir()方法用于获取/data/data/<package name>/cache目录

getFilesDir()方法用于获取/data/data/<package name>/files目录

Environment.getExternalStorageState()方法用于获取SDCard的状态，如果手机装有SDCard，并且可以进行读写，那么方法返回的状态等于Environment.MEDIA_MOUNTED。

Environment.getExternalStorageDirectory()方法用于获取SDCard的目录，当然要获取SDCard的目录，你也可以这样写：

File sdCardDir = new File("/sdcard"); //获取SDCard目录

File saveFile = new File(sdCardDir, "file.txt");

//上面两句代码可以合成一句： File saveFile = new File("/sdcard/file.txt");