Closing nested Reader

Question

When reading from a text file, one typically creates a FileReader and then nests that in a BufferedReader. Which of the two readers should I close when I'm done reading? Does it matter?

FileReader fr = null;
BufferedReader br = null;
try
{
    fr = new FileReader(fileName);
    br = new BufferedReader(fr);
    // ...
}
finally
{
    // should I close fr or br here?
}

I'm a little paranoid when it comes to exception-safety. What happens when the BufferedReader constructor throws an exception? Does it close the nested reader? Or is it guaranteed not to throw?

Answer 1

Generally, close() on the outermost stream wrapper will call close() on the wrapped streams. However, if you think it's likely that a constructor will throw an exception, make liberal use of the Closeable interface.

FileReader fr = new FileReader(fileName);
Closeable res = fr;
try {
    BufferedReader br = new BufferedReader(fr);
    res = br;
} finally {
    res.close();
}

So, even if the JVM ran out of heap space for the buffer and threw an error, you wouldn't leak a file handle.

For Java 7 and above use try-with-resources:

try (FileReader fr = new FileReader(fileName);
    BufferedReader br = new BufferedReader(fr)) {
  // do work
}