在读取/写入文件到内部/外部存储android时使用啥类和方法?
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【中文标题】在读取/写入文件到内部/外部存储android时使用啥类和方法?【英文标题】:What class and method to use while reading/writing a file to internal/external storage android?在读取/写入文件到内部/外部存储android时使用什么类和方法? 【发布时间】:2013-09-01 22:59:00 【问题描述】:我有很多谷歌,阅读 javadoc,并搜索不同的论坛,包括阅读问题,但没有找到我问题的正确答案。下面的代码 sn-p 工作正常,但我想确切地知道在 android 中用于读/写文件的函数。一种可以使用OutputStream,FileOutputSteam.write()写入内部存储,另一种是使用OutputStreamWriter(FileOutputSteam).write(),再使用BufferedWriter(OutputStreamWriter).write(),最后使用PrintWriter.write()。
对于 InputStream 的情况,是否使用 InputStream、FileInputSteam.read()、InputSreamReader(FileInputStream).read()、BufferedReader(InputStreamReader) 也是如此。
我想知道哪种方法最合适。请帮我解决这个问题。
public class MainActivity extends Activity
private static final String TAG = MainActivity.class.getName();
private static final String FILENAME = "students.txt";
private EditText stdId;
private Button Insert;
private Button Search;
private Button Update;
private Button Delete;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final String TAG = MainActivity.class.getName(); //output: com.fyp2.testapp.MainActivity
//value used for insert/delete/search
stdId = (EditText) findViewById(R.id.editTxtId);
//insert value in application sandbox file
Insert = (Button) findViewById(R.id.btnInsert);
Insert.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
String IdToInsert = stdId.getText().toString().trim();
if(IdToInsert.length() > 0)
myInsertFunc(IdToInsert);
else
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
);
//search value from application sandbox file
Search = (Button) findViewById(R.id.btnSearch);
Search.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
String IdToSearch = stdId.getText().toString().trim();
if(IdToSearch.length() > 0)
mySearchFunc(IdToSearch);
else
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
);
//delete value from application sandbox file
Delete = (Button) findViewById(R.id.btnDelete);
Delete.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
String IdToDelete = stdId.getText().toString().trim();
if(IdToDelete.length() > 0)
myDeleteFunc(IdToDelete);
else
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
);
//function to insert
private void myInsertFunc(String data)
//If student id already exist don't write it again -> Not handled at the moment
//Other exceptions may not have been handled properly
try
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput(FILENAME, Context.MODE_APPEND));
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
bufferedWriter.append(data);
bufferedWriter.newLine();
Toast.makeText(getApplicationContext(), "Student ID: " + data + " Inserted Successfully!", Toast.LENGTH_SHORT).show();
bufferedWriter.close();
outputStreamWriter.close();
catch (IOException e)
Log.e(TAG, "File write failed: " + e.toString());
//function to search
private void mySearchFunc(String data)
//Id id not found show toast to user -> Not handled at the moment
try
InputStream inputStream = openFileInput(FILENAME);
if (inputStream != null)
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
while ((receiveString = bufferedReader.readLine()) != null)
if(receiveString.contains(data))
Toast.makeText(getApplicationContext(), "Found Student ID: " + data , Toast.LENGTH_SHORT).show();
break;
bufferedReader.close();
inputStream.close();
catch (FileNotFoundException e)
Log.e(TAG, "File not found: " + e.toString());
catch (IOException e)
Log.e(TAG, "Can not read file: " + e.toString());
private void myDeleteFunc(String data)
/* I have found a solution to delete a specific line from the file.
* But the problem is that it needs to scan the whole file line by line and copy the file contents that not matches the string to temp file.
* This solution can reduce the effeciency. Consider search 20,000 records in a file.
* Need to work around on it.
*/
private void myUpdateFunc(String data)
/* Same goes to the update process...
* Need to scan all records and copy content in temp file and put the updated data in that file.
* Need to work around on this issue too...
*/
@Override
public boolean onCreateOptionsMenu(Menu menu)
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
【问题讨论】:
【参考方案1】:它们都有一个目的。有最好的方法,因为每个作家都是有原因的。如果您有多次读/写/刷新,通常任何缓冲的东西都会更有效。
Android 和 Java 文档都有帮助,Java 文档为您提供了对这些作者的更多描述。查看这些文档。尝试阅读更详细的javase6:
Android_FileWriter
Java_FileWriter
Android_OutputStreamWriter
Java_OutputStreamWriter
Android_BufferedWriter
Java_BufferedWriter
【讨论】:
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