Android之Android的数据存储--SD卡

上一节我们学习了Android的数据存储采用File,但是这样的数据是存储在应用程序内的，那么也就是说这样的存储的文件大小还是有一定要限制的，有时候我们需要存储更大的文件，比如电影等，这就用到了我们的SDSard存储卡。Android也为我们提供了SDCard的一些相关操作。Environment这个类就可以实现这个功能。

Environmet类

常用常量

String MEDIA_MOUNTED	当前Android的外部存储器可读可写
String MEDIA_MOUNTED_READ_ONLY	当前Android的外部存储器只读

常用方法

方法名称	描述
public static File getDataDirectory ()	获得Android下的data文件夹的目录
public static File getDownloadCacheDirectory ()	获得Android Download/Cache 内容的目录
public static File getExternalStorageDirectory ()	获得Android外部存储器也就是SDCard的目录
public static String getExternalStorageState ()	获得Android外部存储器的当前状态
public static File getRootDirectory ()	获得Android下的root文件夹的目录

要想实现对SDCard的读取操作，只需要按以下几个步骤就行：

1、先判断这台手机设备上是否有SDCard且具有读写SDCard的权限

Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)

2、调用Environment.getExternalStorageDirectory()获得到外部存储器的目录

3、使用IO流对外部存储器进行文件的读写

4、别忘记了要在AndroidMainfest.xml中添加权限哦

特别声明：以下操作必须要在如下权限下完成：

[html] view plain copy print ?

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

    <!-- 在SDCard中创建与删除文件权限 -->    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />    <!-- 往SDCard中写入数据权限 -->    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

实例：读写SDCard上的文件

[java] view plain copy print ?

packagecom.jiahui.sdcarddemo;
importjava.io.File;
importjava.io.FileInputStream;
importjava.io.FileNotFoundException;
importjava.io.FileOutputStream;
importjava.io.IOException;
importjava.io.InputStream;
importjava.io.OutputStream;
importjava.io.RandomAccessFile;
importandroid.app.Activity;
importandroid.os.Bundle;
importandroid.os.Environment;
importandroid.view.View;
importandroid.widget.Button;
importandroid.widget.EditText;
importandroid.widget.TextView;
publicclassSDCardDemoActivityextendsActivity{
privateButtonbtnWrite,btnRead;
privateEditTextedtContent;
privateTextViewtvResult;
privatestaticfinalStringFILE_NAME="test.txt";
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
edtContent=(EditText)this.findViewById(R.id.edtContent);
tvResult=(TextView)this.findViewById(R.id.tvResult);
btnRead=(Button)this.findViewById(R.id.btnRead);
btnWrite=(Button)this.findViewById(R.id.btnWrite);
btnWrite.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
System.out.println("往SDCard里写数据");
//先判断是否有SDCard
System.out.println("Environment.getExternalStorageState():"
+Environment.getExternalStorageState());
System.out.println("Environment.MEDIA_MOUNTED:"
+Environment.MEDIA_MOUNTED);
if(Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)){
Stringcontent=edtContent.getText().toString();
try{
//获取SDcard路径
FilesdCardDir=Environment
.getExternalStorageDirectory();
//SDCard目录：/mnt/sdcard
StringsdcardPath=sdCardDir.getAbsolutePath();
System.out.println("sdCardDir.getAbsolutePath()"
+sdCardDir.getAbsolutePath());
Filefile=newFile(sdCardDir,FILE_NAME);
//Filefile=newFile(sdcardPath
//+File.separator+FILE_NAME);
//以指定文件创建RandomAccessFile对象
RandomAccessFileraf=newRandomAccessFile(file,"rw");
//将文件记录指针移动最后
raf.seek(file.length());
//输出文件内容
raf.write(content.getBytes());
raf.close();
}catch(Exceptione){
//TODO:handleexception
}
}
}
});
btnRead.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
if(Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)){
//获取SDcard路径
StringBuildersb=newStringBuilder();
try{
FilesdCardDir=Environment
.getExternalStorageDirectory();
Filefile=newFile(sdCardDir,FILE_NAME);
InputStreaminputStream=newFileInputStream(file);
intlen=0;
byte[]buffer=newbyte[1024];
while((len=inputStream.read(buffer))!=-1){
sb.append(newString(buffer,0,len));
}
tvResult.setText(sb.toString());
//关闭流
inputStream.close();
}catch(Exceptione){
//TODOAuto-generatedcatchblock
e.printStackTrace();
}
}
}
});
}
}

package com.jiahui.sdcarddemo;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.io.RandomAccessFile;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;public class SDCardDemoActivity extends Activity {private Button btnWrite, btnRead;private EditText edtContent;private TextView tvResult;private static final String FILE_NAME = "test.txt";public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);edtContent = (EditText) this.findViewById(R.id.edtContent);tvResult = (TextView) this.findViewById(R.id.tvResult);btnRead = (Button) this.findViewById(R.id.btnRead);btnWrite = (Button) this.findViewById(R.id.btnWrite);btnWrite.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {System.out.println("往SDCard里写数据");// 先判断是否有SDCardSystem.out.println("Environment.getExternalStorageState():"+ Environment.getExternalStorageState());System.out.println("Environment.MEDIA_MOUNTED:"+ Environment.MEDIA_MOUNTED);if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {String content = edtContent.getText().toString();try {// 获取SDcard路径File sdCardDir = Environment.getExternalStorageDirectory();// SDCard目录：/mnt/sdcardString sdcardPath = sdCardDir.getAbsolutePath();System.out.println("sdCardDir.getAbsolutePath()"+ sdCardDir.getAbsolutePath());File file = new File(sdCardDir, FILE_NAME);// File file = new File(sdcardPath// + File.separator + FILE_NAME);// 以指定文件创建RandomAccessFile对象RandomAccessFile raf = new RandomAccessFile(file, "rw");// 将文件记录指针移动最后raf.seek(file.length());// 输出文件内容raf.write(content.getBytes());raf.close();} catch (Exception e) {// TODO: handle exception}}}});btnRead.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {// 获取SDcard路径StringBuilder sb = new StringBuilder();try {File sdCardDir = Environment.getExternalStorageDirectory();File file = new File(sdCardDir, FILE_NAME);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));}tvResult.setText(sb.toString());// 关闭流inputStream.close();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}});}}

实现效果

用File Explorer可以看到如下图一样的效果：

开发注意事项：

1、一定不能忘记添加权限

[html] view plain copy print ?

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

    <!-- 在SDCard中创建与删除文件权限 -->    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />    <!-- 往SDCard中写入数据权限 -->    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

2、要判断一下是否插入SD卡和是否具有读写的能力：

Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)

如需转载引用请注明出处：http://blog.csdn.net/jiahui524

源代码下载：http://download.csdn.net/download/jiahui524/3799819

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