4.6.1.1 使用私有文件

这种情况下使用的文件，只能在同一个应用中读取/写入，并且这是使用文件的一种非常安全的方式。 原则上，无论存储在文件中的信息是否是公开的，尽可能使用私有文件，当与其他应用交换必要的信息时，应该使用另一个 Android 系统（内容供应器，服务）来完成。

要点：

1. 文件必须在应用目录中创建。

2. 文件的访问权限必须设置为私有模式，以免其他应用使用。

3. 可以存储敏感信息。

4. 对于存储在文件中的信息，请仔细和安全地处理文件数据。

PrivateFileActivity.java

package org.jssec.android.file.privatefile;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class PrivateFileActivity extends Activity {
    private TextView mFileView;
    private static final String FILE_NAME = "private_file.dat";
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.file);
        mFileView = (TextView) findViewById(R.id.file_view);
    }
    
    /**
    * Create file process
    *
    * @param view
    */
    public void onCreateFileClick(View view) {
        FileOutputStream fos = null;
        try {
            // *** POINT 1 *** Files must be created in application directory.
            // *** POINT 2 *** The access privilege of file must be set private mode in order not to be used by other applications.
            fos = openFileOutput(FILE_NAME, MODE_PRIVATE);
            // *** POINT 3 *** Sensitive information can be stored.
            // *** POINT 4 *** Regarding the information to be stored in files, handle file data carefully and securely.
            // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
            fos.write(new String("Not sensotive information (File Activity)¥n").getBytes());
        } catch (FileNotFoundException e) {
            mFileView.setText(R.string.file_view);
        } catch (IOException e) {
            android.util.Log.e("PrivateFileActivity", "failed to read file");
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    android.util.Log.e("PrivateFileActivity", "failed to close file");
                }
            }
        }
        finish();
    }
    
    /**
    * Read file process
    *
    * @param view
    */
    public void onReadFileClick(View view) {
        FileInputStream fis = null;
        try {
            fis = openFileInput(FILE_NAME);
            byte[] data = new byte[(int) fis.getChannel().size()];
            fis.read(data);
            String str = new String(data);
            mFileView.setText(str);
        } catch (FileNotFoundException e) {
            mFileView.setText(R.string.file_view);
        } catch (IOException e) {
            android.util.Log.e("PrivateFileActivity", "failed to read file");
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    android.util.Log.e("PrivateFileActivity", "failed to close file");
                }
            }
        }
    }
    
    /**
    * Delete file process
    *
    * @param view
    */
    public void onDeleteFileClick(View view) {
        File file = new File(this.getFilesDir() + "/" + FILE_NAME);
        file.delete();
        mFileView.setText(R.string.file_view);
    }
}

PrivateUserActivity.java

package org.jssec.android.file.privatefile;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class PrivateUserActivity extends Activity {

    private TextView mFileView;
    private static final String FILE_NAME = "private_file.dat";
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.user);
        mFileView = (TextView) findViewById(R.id.file_view);
    }
    
    private void callFileActivity() {
        Intent intent = new Intent();
        intent.setClass(this, PrivateFileActivity.class);
        startActivity(intent);
    }
    
    /**
    * Call file Activity process
    *
    * @param view
    */
    public void onCallFileActivityClick(View view) {
        callFileActivity();
    }
    
    /**
    * Read file process
    *
    * @param view
    */
    public void onReadFileClick(View view) {
        FileInputStream fis = null;
        try {
            fis = openFileInput(FILE_NAME);
            byte[] data = new byte[(int) fis.getChannel().size()];
            fis.read(data);
            // *** POINT 4 *** Regarding the information to be stored in files, handle file data carefully and securely.
            // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
            String str = new String(data);
            mFileView.setText(str);
        } catch (FileNotFoundException e) {
            mFileView.setText(R.string.file_view);
        } catch (IOException e) {
            android.util.Log.e("PrivateUserActivity", "failed to read file");
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    android.util.Log.e("PrivateUserActivity", "failed to close file");
                }
            }
        }
    }
    
    /**
    * Rewrite file process
    *
    * @param view
    */
    public void onWriteFileClick(View view) {
        FileOutputStream fos = null;
        try {
            // *** POINT 1 *** Files must be created in application directory.
            // *** POINT 2 *** The access privilege of file must be set private mode in order not to be used by other applications.
            fos = openFileOutput(FILE_NAME, MODE_APPEND);
            // *** POINT 3 *** Sensitive information can be stored.
            // *** POINT 4 *** Regarding the information to be stored in files, handle file data carefully and securely.
            // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
            fos.write(new String("Sensitive information (User Activity)¥n").getBytes());
        } catch (FileNotFoundException e) {
            mFileView.setText(R.string.file_view);
        } catch (IOException e) {
            android.util.Log.e("PrivateUserActivity", "failed to read file");
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    android.util.Log.e("PrivateUserActivity", "failed to close file");
                }
            }
        }
        callFileActivity();
    }
}