Force IOException during file reading

Question

I have a piece of code that reads data from a file. I want to force IOException in this code for testing purposes (I want to check if the code throws a correct custom exception in this case).

Is there any way to create a file which is protected from being read, for example? Maybe dealing with some security checks can help?

Please, note that passing the name of a non-existent file cannot help, because FileNotFoundException has a separate catch clause.

Here is the piece of code for better understanding of the question:

    BufferedReader reader = null;     try {          reader = new BufferedReader(new FileReader(csvFile));          String rawLine;         while ((rawLine = reader.readLine()) != null) {             // some work is done here         }      } catch (FileNotFoundException e) {         throw new SomeCustomException();     } catch (IOException e) {         throw new SomeCustomException();     } finally {         // close the input stream         if (reader != null) {             try {                 reader.close();             } catch (IOException e) {                 // ignore             }         }     } 

Answer 1

Disclaimer: I have not tested this on a non-Windows platform, so it may have different results on a platform with different file locking characteristics.

If you lock the file beforehand, you can trigger an IOException when something attempts to read from it:

java.io.IOException: The process cannot access the file because another process has locked a portion of the file 

This works even if you are in the same thread.

Here's some sample code:

final RandomAccessFile raFile = new RandomAccessFile(csvFile, "rw"); raFile.getChannel().lock();