Re: IO pattern

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Sat, 11 Dec 2010 14:54:58 -0500

Message-ID:

<ie0kt1$9nt$1@news.albasani.net>

markspace wrote:

I've done something similar as a simple utility method. Typed from
memory, not checked:

public void closeAll( Closeable... closeables ) {
{
   for( Closeable c : closeables ) {
     try {
       if( c != null ) {
         c.close();
       }
     } catch( IOException ex ) {
       logger.log( Level.SEVERE, null, ex );
     }
   }
}

The check for null is there to catch the case where the reference has
not been initialized yet. Maybe we throw an exception trying to open the
file, for example, and no object was returned.

I recommend "RAII". (I call it "RRID", "resource release in disposal".) Null
resource handlers are not possible with certain idioms. For this utility
method the 'null' check is mandatory, but in private code might not be.

  public void foo()
  {
    final Reader reader;
    try
    {
      reader = new BufferedReader( new FileReader( "foo" ));
    }
    catch ( IOException exc )
    {
      final String msg = "Cannot open reader";
      logger.error( msg, exc );
      return;
    }
    assert reader != null;
    try
    {
      doSomething( reader );
    }
    catch ( IOException exc )
    {
      final String msg = "Problem with reader";
      logger.error( msg, exc );
    }
    finally
    {
      close( reader );
    }
  }
  private void close( Reader reader )
  {
    assert reader != null;
    try
    {
      reader.close();
    }
    catch ( IOException exc )
    {
      final String msg = "Cannot close reader";
      logger.error( msg, exc );
    }
  }

--
Lew