Apache Commons IO Introduction

The Apache Commons project is a collection of over 40 individual Java libraries that provide convenience methods to eleviate the developer from having to write tedious, boiler-plate code. The libraries try to stay as close to the core Java API as possible, so they have few or no dependencies on other libraries.

One of the libraries that I use a lot is the IO library. It contains features that build upon the core Java IO API and also make it easier to interact with the filesystem. I'm going to list three of the methods that I use a lot (and that you should use too). Looking at the API though, there's a ton more stuff this library can do, so don't let my tiny blog post keep you from exploring it.

IOUtils.copy()

The IOUtils.copy() method is great for copying data from an InputStream (or Reader) to an OutputStream (or Writer). No more creating arbitrarily-sized buffers and parenthesis-laden while loops! What it does here isn't rocket-science--any programmer worth their salt could code this up themselves. The point of using it is to make your code easier to read, less error-prone, and more consistent with the broader Java programming community.

These two code samples show just how much less code you have to write if you use this method:

Plain Java:

InputStream in = ...
OutputStream out = ...
byte buffer[] = new byte[4096];
int read;
while ((read = in.read(buffer)) != -1){
  out.write(buffer, 0, read);
}
in.close();
out.close();

Commons IO:

InputStream in = ...
OutputStream out = ...
IOUtils.copy(in, out);
in.close();
out.close();

IOUtils.closeQuietly()

The IOUtils.closeQuietly() method eliminates the boiler-plate required to close a stream in Java. It (1) checks to make sure the stream isn't null, (2) closes the stream, and (3) catches the IOException that is thrown when the stream's close() method is called. Again, what it does here isn't rocket-science. Its purpose is to reduce the amount of fluff in your code:

Plain Java:

InputStream in = null;
try{
  in = ...
  ...
} catch (IOException e){
  ...
} finally{
  try{
    if (in != null){
      in.close();
    }
  } catch (IOException e){}
}

Commons IO:

InputStream in = null;
try{
  in = ...
  ...
} catch (IOException e){
  ...
} finally{
  IOUtils.closeQuietly(in);
}

FileUtils.writeStringToFile()

Whenever I switch from coding in PHP to coding in Java, my heart sinks a little bit when I have to write some text to a file. In PHP, you can do this with a single function call. But in Java, you need to write a dozen or so lines of code. The FileUtils.writeStringToFile() method, however, allows you to write text to a file in one fell swoop.

Plain Java:

String text = "some text";
File file = new File("myfile.txt");
Writer writer = null;
try{
  writer = new PrintWriter(file);
  writer.write(text);
} catch (IOException e){
  ...
} finally {
  if (writer != null){
    try{
      writer.close();
    } catch (IOException e){}
  }
}

Commons IO:

String text = "some text";
File file = new File("myfile.txt");
try{
  FileUtils.writeStringToFile(file, text);
} catch (IOException e){
  ...
}

I hope you've enjoyed my little introduction to Commons IO. Using this library can greatly increase the readability and reliability of your code.