Android - 如何序列化和去序列化公共外部存储的对象？

Question

我需要将对象保存到公共外部存储器（http://developer.android.com/guide/topics/data/data-storage.html#filesExternal）请向下滚动到“保存应共享的文件”，即保存文件，以便在卸载应用程序时不会被删除。

保存后，我需要从保存的文件中加载对象并显示它。只是使用int对象进行测试。请帮忙。

这是我为保存和加载

int a = 1; 
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) 
{ 
    String path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString(); 
    final File file = new File (path, "int_object_saved.dat"); 

    FileOutputStream file_output_stream = null; 
    ObjectOutputStream object_output_stream = null; 
    boolean should_keep_file = true; 

    try 
    { 
     file_output_stream = new FileOutputStream(file); 
     object_output_stream = new ObjectOutputStream(file_output_stream); 
     object_output_stream.writeObject(a); 

    } 
    catch (FileNotFoundException e) 
    { 
     e.printStackTrace(); 
     should_keep_file = false; 
    } 
    catch (IOException e) 
    { 
     e.printStackTrace(); 
     should_keep_file = false; 
    } 
    finally 
    { 
     try 
     { 
      if(object_output_stream != null) 
       object_output_stream.close(); 

      if(file_output_stream != null) 
       file_output_stream.close(); 

      if(!should_keep_file) 
       file.delete(); 
     } 
     catch (Exception e) 
     { 
      e.printStackTrace(); 
     } 
    } 
} 
else 
{ 
    Log.d("mytag", "Sorry can't write to external media"); 
} 

int b = 0; 
try 
{ 
    FileInputStream file_input_stream; 
    file_input_stream = activity_parameter.openFileInput("int_object_saved.dat"); 
    ObjectInputStream object_input_stream = new ObjectInputStream(file_input_stream); 
    b = (Integer) object_input_stream.readObject(); 
    object_input_stream.close(); 
} 
catch (FileNotFoundException e) 
{ 
    e.printStackTrace(); 
} 
catch (OptionalDataException e) 
{ 
    e.printStackTrace(); 
} 
catch (ClassNotFoundException e) 
{ 
    e.printStackTrace(); 
} 
catch (IOException e) 
{ 
    e.printStackTrace(); 
} 

Log.d("mytag", Integer.toString(b)); 

码这是logcat的我得到

08-02 12:39:48.382: I/ApplicationPackageManager(13109): cscCountry is not German : BTU 
08-02 12:39:48.421: D/mytag(13109): my Log is working :D 
08-02 12:39:48.437: W/System.err(13109): java.io.FileNotFoundException: /data/data/j.violajones.facedetect1/files/int_object_saved.dat (No such file or directory) 
08-02 12:39:48.437: W/System.err(13109): at org.apache.harmony.luni.platform.OSFileSystem.open(Native Method) 
08-02 12:39:48.437: W/System.err(13109): at dalvik.system.BlockGuard$WrappedFileSystem.open(BlockGuard.java:232) 
08-02 12:39:48.437: W/System.err(13109): at java.io.FileInputStream.<init>(FileInputStream.java:80) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ContextImpl.openFileInput(ContextImpl.java:416) 
08-02 12:39:48.437: W/System.err(13109): at android.content.ContextWrapper.openFileInput(ContextWrapper.java:152) 
08-02 12:39:48.437: W/System.err(13109): at j.violajones.facedetect1.Detector.<init>(Detector.java:94) 
08-02 12:39:48.437: W/System.err(13109): at j.violajones.facedetect1.Camera_Activty.onCreate(Camera_Activty.java:72) 
08-02 12:39:48.437: W/System.err(13109): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 
08-02 12:39:48.437: W/System.err(13109): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-02 12:39:48.437: W/System.err(13109): at android.os.Looper.loop(Looper.java:130) 
08-02 12:39:48.437: W/System.err(13109): at android.app.ActivityThread.main(ActivityThread.java:3687) 
08-02 12:39:48.445: W/System.err(13109): at java.lang.reflect.Method.invokeNative(Native Method) 
08-02 12:39:48.445: W/System.err(13109): at java.lang.reflect.Method.invoke(Method.java:507) 
08-02 12:39:48.445: W/System.err(13109): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
08-02 12:39:48.445: W/System.err(13109): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
08-02 12:39:48.445: W/System.err(13109): at dalvik.system.NativeStart.main(Native Method) 
08-02 12:39:48.445: D/mytag(13109): 0 

，这是我的AndroidManifest.xml文件

<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="j.violajones.facedetect1" 
    android:versionCode="1" 
    android:versionName="1.0" > 

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

    <uses-feature android:name="android.hardware.camera" /> 
    <uses-feature android:name="android.hardware.camera.autofocus" /> 

    <uses-sdk 
     android:minSdkVersion="8" 
     android:targetSdkVersion="15" /> 

    <application 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name=".Camera_Activty" 
      android:label="@string/title_activity_camera__activty" 
      android:screenOrientation="landscape" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

Answer 1

错误信息是明确的：

java.io.FileNotFoundException: /data/data/j.violajones.facedetect1/files/int_object_saved.dat (No such file or directory) 

您不必在/data/data/j.violajones.facedetect1/files/int_object_saved.dat

事实上这样的文件，你似乎并没有被写入该位置，因为你使用：

String path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString(); 
final File file = new File (path, "int_object_saved.dat"); 

因此，尝试从位置在哪里阅读你保存它：

String path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString(); 
FileInputStream file_input_stream = new FileInputStream(path + "/int_object_saved.dat"); 
/*...*/