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：　　

 1 package com.example.android_data_storage_sdcard.file;
 2
 3 import java.io.File;
 4 import java.io.FileNotFoundException;
 5 import java.io.FileOutputStream;
 6 import java.io.IOException;
 7
 8 import android.os.Environment;
 9 import android.util.Log;
10 /**
11  * @author xiaowu
12  * @note  文件存储之外部存储（sdcard存储）。
13  *         外部存储不需要context
14  */
15 public class FileUitls {
16     private final String TAG = "FileUtil";
17
18     /**
19      * 保存文件至外部存储的SD卡
20      *
21      * @param fileName
22      * @param mode
23      * @param data
24      * @return
25      */
26     public boolean saveFileToSdcard(String fileName,  byte[] data) {
27         boolean flag = false;
28         // 判断sdcard的状态
29         String state = Environment.getExternalStorageState();
30         // 获取sdcard的根目录 /mnt/sdcard/...
31         File root = Environment.getExternalStorageDirectory();
32         FileOutputStream outputStream = null;
33         // Environment.MEDIA_MOUNTED表示SD卡挂载在手机上并可以读写
34         if (Environment.MEDIA_MOUNTED.equals(state)) {
35             // 在sdcard的根目录下创建文件
36             File file = new File(root, fileName);
37             try {
38                 outputStream = new FileOutputStream(file);
39                 outputStream.write(data, 0, data.length);
40                 flag = true ;
41             } catch (FileNotFoundException e) {
42                 Log.i(TAG, "文件未找到异常！");
43             } catch (Exception e) {
44                 Log.i(TAG, "写文件发生异常");
45             } finally {
46                 if (outputStream != null) {
47                     try {
48                         outputStream.close();
49                     } catch (IOException e) {
50                         Log.i(TAG, "关闭IO流发生异常!");
51                     }
52                 }
53             }
54         }
55         return flag;
56     }
57 }

　　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>

 1 package com.example.android_data_storage_sdcard;
 2
 3 import android.test.AndroidTestCase;
 4
 5 import com.example.android_data_storage_sdcard.file.FileUitls;
 6
 7 public class MyTest extends AndroidTestCase {
 8
 9     public void test() {
10         FileUitls fileUitls = new FileUitls();
11         fileUitls.saveFileToSdcard("keji.txt", "橘子洲头".getBytes());
12     }
13 }