4.6.1.2 使用公共只读文件
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2023-12-01
4.6.1.2 使用公共只读文件
这是使用文件向未指定的大量应用公开内容的情况。 如果通过遵循以下几点来实现，那么它也是比较安全的文件使用方法。 请注意，在 API 级别 1 7及更高版本中，不推荐使用MODE_WORLD_READABLE变量来创建公共文件，并且在 API 级别 24 及更高版本中，会触发安全异常; 因此使用内容供应器的文件共享方法更可取。
要点：
文件必须在应用目录中创建。
文件的访问权限必须设置为其他应用只读。
敏感信息不得存储。
对于要存储在文件中的信息，请仔细和安全地处理文件数据。
PublicFileActivity.java
package org.jssec.android.file.publicfile.readonly;
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 PublicFileActivity extends Activity {
private TextView mFileView;
private static final String FILE_NAME = "public_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 to read only to other applications.
// (MODE_WORLD_READABLE is deprecated API Level 17,
// don't use this mode as much as possible and exchange data by using ContentProvider().)
fos = openFileOutput(FILE_NAME, MODE_WORLD_READABLE);
// *** POINT 3 *** Sensitive information must not 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 sensitive information (Public File Activity)¥n").getBytes());
} catch (FileNotFoundException e) {
mFileView.setText(R.string.file_view);
} catch (IOException e) {
android.util.Log.e("PublicFileActivity", "failed to read file");
} finally {
if (fos != null) {
try {
fos.close();
} catch (IOException e) {
android.util.Log.e("PublicFileActivity", "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("PublicFileActivity", "failed to read file");
} finally {
if (fis != null) {
try {
fis.close();
} catch (IOException e) {
android.util.Log.e("PublicFileActivity", "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);
}
}
PublicUserActivity.java
package org.jssec.android.file.publicuser.readonly;
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.content.ActivityNotFoundException;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class PublicUserActivity extends Activity {
private TextView mFileView;
private static final String TARGET_PACKAGE = "org.jssec.android.file.publicfile.readonly";
private static final String TARGET_CLASS = "org.jssec.android.file.publicfile.readonly.PublicFileActivity";
private static final String FILE_NAME = "public_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.setClassName(TARGET_PACKAGE, TARGET_CLASS);
try {
startActivity(intent);
} catch (ActivityNotFoundException e) {
mFileView.setText("(File Activity does not exist)");
}
}
/**
* 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 {
File file = new File(getFilesPath(FILE_NAME));
fis = new FileInputStream(file);
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) {
android.util.Log.e("PublicUserActivity", "no file");
} catch (IOException e) {
android.util.Log.e("PublicUserActivity", "failed to read file");
} finally {
if (fis != null) {
try {
fis.close();
} catch (IOException e) {
android.util.Log.e("PublicUserActivity", "failed to close file");
}
}
}
}
/**
* Rewrite file process
*
* @param view
*/
public void onWriteFileClick(View view) {
FileOutputStream fos = null;
boolean exception = false;
try {
File file = new File(getFilesPath(FILE_NAME));
// Fail to write in. FileNotFoundException occurs.
fos = new FileOutputStream(file, true);
fos.write(new String("Not sensitive information (Public User Activity)¥n").getBytes());
} catch (IOException e) {
mFileView.setText(e.getMessage());
exception = true;
} finally {
if (fos != null) {
try {
fos.close();
} catch (IOException e) {
exception = true;
}
}
}
if (!exception)
callFileActivity();
}
private String getFilesPath(String filename) {
String path = "";
try {
Context ctx = createPackageContext(TARGET_PACKAGE,
Context.CONTEXT_RESTRICTED);
File file = new File(ctx.getFilesDir(), filename);
path = file.getPath();
} catch (NameNotFoundException e) {
android.util.Log.e("PublicUserActivity", "no file");
}
return path;
}
}