android 开发-文件存储之读写sdcard

　　android提供对可移除的外部存储进行文件存储。在对外部sdcard进行调用的时候首先要调用Environment.getExternalStorageState()检查sdcard的可用状态。通过Environment.getExternalStorageDirectory()得到Sdcard的路径。文件写入外部存储需要添加对sdcard的授权

　　<!-- 写sdcard需要添加写sdcard的授权 -->
　　<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

　　boolean mExternalStorageAvailable = false;
　　boolean mExternalStorageWriteable = false;
　　String state = Environment.getExternalStorageState();

　　if (Environment.MEDIA_MOUNTED.equals(state)) {
 　　   // We can read and write the media
   　　 mExternalStorageAvailable = mExternalStorageWriteable = true;
　　} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
 　　   // We can only read the media
　　    mExternalStorageAvailable = true;
 　　   mExternalStorageWriteable = false;
　　} else {
 　　   // Something else is wrong. It may be one of many other states, but all we need
 　　   //  to know is we can neither read nor write
　　    mExternalStorageAvailable = mExternalStorageWriteable = false;
　　}
android学习过程中的示例如下：
　　文件读写工具类：
　　

 package com.example.android_data_storage_sdcard.file;

 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.os.Environment;
 import android.util.Log;
 /**
  * @author xiaowu
  * @note  文件存储之外部存储（sdcard存储）。
  *         外部存储不需要context
  */
 public class FileUitls {
     private final String TAG = "FileUtil";

     /**
      * 保存文件至外部存储的SD卡
      * @param fileName
      * @param mode
      * @param data
      * @return 是否存储内容到sdcard成功
      */
     public boolean saveFileToSdcard(String fileName,  byte[] data) {
         boolean flag = false;
         // 判断sdcard的状态
         String state = Environment.getExternalStorageState();
         // 获取sdcard的根目录 /mnt/sdcard/...
         File root = Environment.getExternalStorageDirectory();
         FileOutputStream outputStream = null;
         // Environment.MEDIA_MOUNTED表示SD卡挂载在手机上并可以读写
         if (Environment.MEDIA_MOUNTED.equals(state)) {
             // 在sdcard的根目录下创建文件
             File file = new File(root, fileName);
             try {
                 outputStream = new FileOutputStream(file);
                 outputStream.write(data, 0, data.length);
                 flag = true ;
             } catch (FileNotFoundException e) {
                 Log.i(TAG, "文件未找到异常！");
             } catch (Exception e) {
                 Log.i(TAG, "写文件发生异常");
             } finally {
                 if (outputStream != null) {
                     try {
                         outputStream.close();
                     } catch (IOException e) {
                         Log.i(TAG, "关闭IO流发生异常!");
                     }
                 }
             }
         }
         return flag;
     }
     /**
      * 从sdcard中读文件
      * @param fileName
      * @return 文件内容
      */
     public String  readFromSdcard(String fileName){
         String  str = "" ;
         FileInputStream inputStream = null;
         String state = Environment.getExternalStorageState();
         ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
         try {
             if (Environment.MEDIA_MOUNTED.equals(state)) {
                 //获取Sdcard路径
                 File root = Environment.getExternalStorageDirectory();
                 File file = new File(root.getAbsolutePath(),fileName);
                 if(file.exists()){
                     inputStream = new FileInputStream(file);
                     int len = 0 ;
                     byte[] data = new byte[1024];
                     while ((len = inputStream.read(data)) != -1) {
                         byteArrayOutputStream.write(data, 0, len);
                     }
                     return new String(byteArrayOutputStream.toByteArray());
                 }
             }
         } catch (Exception e) {
             Log.i(TAG, "文件读取异常！");
         }finally{
             if(inputStream != null){
                 try {
                     inputStream.close();
                 } catch (IOException e) {
                     Log.i(TAG, "关闭流异常！");
                 }
             }
         }
         return str ;
     }
 }

　　Junit单元测试类：

　　单元测试类必须继承自AndroidTestCase，并在资源清单文件中添加单元测试包  <uses-library android:name="android.test.runner"/>,并添加单元测试目标包

　　<!-- 引入单元测试目标包 -->
　　<instrumentation
　　　　android:name="android.test.InstrumentationTestRunner"
　　　　android:targetPackage="com.example.android_data_storage_sdcard" >
　　</instrumentation>

 package com.example.android_data_storage_sdcard;

 import android.test.AndroidTestCase;

 import com.example.android_data_storage_sdcard.file.FileUitls;

 public class MyTest extends AndroidTestCase {

     public void test() {
         FileUitls fileUitls = new FileUitls();
         fileUitls.saveFileToSdcard("keji.txt", "橘子洲头".getBytes());
     }
 }