使用Activity的openFileOutput()方法保存文件，文件是存放在手机空间上，一般手机的存储空间不是很大，存放些小文件还行，如果要存放像视频这样的大文件，是不可行的。对于像视频这样的大文件，我们可以把它存放在SDCard。 SDCard是干什么的？你可以把它看作是移动硬盘或U盘。
在模拟器中使用SDCard，你需要先创建一张SDCard卡（当然不是真的SDCard，只是镜像文件）。创建SDCard可以在Eclipse创建模拟器时随同创建，也可以使用DOS命令进行创建，如下：在Dos窗口中进入android SDK安装路径的tools目录，输入以下命令创建一张容量为2G的SDCard，文件后缀可以随便取，建议使用.img：
mksdcard 2048M D:\AndroidTool\sdcard.img
注意：在程序中访问SDCard，你需要申请访问SDCard的权限。
在AndroidManifest.xml中加入访问SDCard的权限如下:<!-- 在SDCard中创建与删除文件权限 --><uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/><!-- 往SDCard写入数据权限 --><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>要往SDCard存放文件，程序必须先判断手机是否装有SDCard，并且可以进行读写。注意：访问SDCard必须在AndroidManifest.xml中加入访问SDCard的权限if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录 File saveFile = new File(sdCardDir, “ljq.txt”); FileOutputStream outStream = new FileOutputStream(saveFile); outStream.write("abc".getBytes()); outStream.close();}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("/mnt/sdcard"); //获取SDCard目录File saveFile = new File(sdCardDir, "ljq.txt"); //上面两句代码可以合成一句： File saveFile = new File("/mnt/sdcard/ljq.txt");FileOutputStream outStream = new FileOutputStream(saveFile);outStream.write("abc".getBytes());outStream.close();
案例
main.xml布局文件
<? xml version="1.0" encoding="utf-8" ?> < LinearLayout xmlns:android ="http://schemas.android.com/apk/res/android" android:orientation ="vertical" android:layout_width ="fill_parent" android:layout_height ="fill_parent" > <!-- 相对布局 --> < RelativeLayout xmlns:android ="http://schemas.android.com/apk/res/android" android:orientation ="vertical" android:layout_width ="fill_parent" android:layout_height ="wrap_content" > < TextView android:layout_width ="wrap_content" android:layout_height ="wrap_content" android:text ="@string/filename" android:id ="@+id/filenameLable" /> < EditText android:layout_width ="250px" android:layout_height ="wrap_content" android:layout_toRightOf ="@id/filenameLable" android:layout_alignTop ="@id/filenameLable" android:layout_marginLeft ="10px" android:text ="ljq.txt" android:id ="@+id/filename" /> </ RelativeLayout > < TextView android:layout_width ="fill_parent" android:layout_height ="wrap_content" android:text ="@string/content" /> < EditText android:layout_width ="fill_parent" android:layout_height ="wrap_content" android:minLines ="3" android:id ="@+id/content" /> < RelativeLayout xmlns:android ="http://schemas.android.com/apk/res/android" android:orientation ="vertical" android:layout_width ="fill_parent" android:layout_height ="wrap_content" > < Button android:layout_width ="wrap_content" android:layout_height ="wrap_content" android:text ="@string/button" android:id ="@+id/button" /> < Button android:layout_width ="wrap_content" android:layout_height ="wrap_content" android:layout_toRightOf ="@id/button" android:layout_alignTop ="@id/button" android:layout_marginLeft ="10px" android:minLines ="3" android:text ="@string/readButton" android:id ="@+id/readButton" /> </ RelativeLayout > < TextView android:layout_width ="wrap_content" android:layout_height ="wrap_content" android:id ="@+id/resultView" /> </ LinearLayout >
strings.xml
<? xml version = " 1.0 " encoding = " utf-8 " ?> < resources > < string name = " hello " > Hello World, FileActivity !</ string > < string name = " app_name " > 数据保存 </ string > < string name = " filename " > 文件名称 </ string > < string name = " content " > 文件内容 </ string > < string name = " button " > 保存 </ string > < string name = " readButton " > 读取内容 </ string > < string name = " error " > 保存失败 </ string > < string name = " success " > 保存成功 </ string > </ resources >
FileService工具类
package com.ljq.service; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.io.OutputStream; public class FileService { /** * 保存数据 * * @param outputStream * @param content * @throws Exception */ public static void save(OutputStream outputStream, String content) throws Exception { outputStream.write(content.getBytes()); outputStream.close(); } /** * 读取数据 * * @param inputStream * @return * @throws Exception */ public static String read(InputStream inputStream) throws Exception { ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); // 往内存写数据 byte [] buffer = new byte [ 1024 ]; // 缓冲区 int len = - 1 ; while ((len = inputStream.read(buffer)) != - 1 ) { byteArrayOutputStream.write(buffer, 0 , len); } byte [] data = byteArrayOutputStream.toByteArray(); // 存储数据 byteArrayOutputStream.close(); inputStream.close(); return new String(data); }}
SdcardActivity类
package com.ljq.sdcard; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.InputStream; import android.app.Activity; import android.os.Bundle; import android.os.Environment; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; import android.widget.Toast; import com.ljq.service.FileService; public class SdcardActivity extends Activity { private final String TAG = " FileActivity " ; private EditText filenameText; private TextView resultView; private EditText contentText; @Override public void onCreate(Bundle savedInstanceState) { super .onCreate(savedInstanceState); setContentView(R.layout.main); filenameText = (EditText) this .findViewById(R.id.filename); contentText = (EditText) this .findViewById(R.id.content); resultView = (TextView) this .findViewById(R.id.resultView); Button button = (Button) this .findViewById(R.id.button); button.setOnClickListener(listener); Button readButton = (Button) this .findViewById(R.id.readButton); readButton.setOnClickListener(listener); } private View.OnClickListener listener = new View.OnClickListener() { public void onClick(View v) { Button button = (Button) v; String filename = filenameText.getText().toString(); // Environment.getExternalStorageDirectory()等价于new File("/sdcard")---->获取sdcard目录 // 获取sdcard目录 // File file = new File("/sdcard" + filename); File file = new File(Environment.getExternalStorageDirectory(), filename); switch (button.getId()) { case R.id.button: int resId = R.string.success; // 默认成功 String content = contentText.getText().toString(); // sdcard存在并且可以读写 if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) { try { FileOutputStream fileOutputStream = new FileOutputStream(file); FileService.save(fileOutputStream, content); } catch (Exception e) { Log.e(TAG, e.toString()); resId = R.string.error; } Toast.makeText(SdcardActivity. this , resId, Toast.LENGTH_LONG).show(); } else { Toast.makeText(SdcardActivity. this , " sdcard不存在或写保护 " , Toast.LENGTH_LONG).show(); } break ; case R.id.readButton: try { InputStream inputStream = new FileInputStream(file); String text = FileService.read(inputStream); resultView.setText(text); } catch (Exception e) { Log.e(TAG, e.toString()); Toast.makeText(SdcardActivity. this , " 读取失败 " , Toast.LENGTH_LONG).show(); } break ; } } };}
清单文件
<? xml version="1.0" encoding="utf-8" ?> < manifest xmlns:android ="http://schemas.android.com/apk/res/android" package ="com.ljq.sdcard" android:versionCode ="1" android:versionName ="1.0" > < application android:icon ="@drawable/icon" android:label ="@string/app_name" > < activity android:name =".SdcardActivity" android:label ="@string/app_name" > < intent-filter > < action android:name ="android.intent.action.MAIN" /> < category android:name ="android.intent.category.LAUNCHER" /> </ intent-filter > </ activity > </ application > < uses-sdk android:minSdkVersion ="7" /> <!-- 在SDCard中创建与删除文件权限 --> < uses-permission android:name ="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <!-- 往SDCard写入数据权限 --> < uses-permission android:name ="android.permission.WRITE_EXTERNAL_STORAGE" /> </ manifest >
运行结果
