Scala, output to multiple files/streams

Question

I need to write the same text to multiple files (or streams). Sometimes I need to use Writer, sometimes a PrintWriter, sometimes a OutputStream...

One way to do this in Java wold be to extend a PrintWriter to have an array of PrintWriters and overridde each method as follows:

class MutiplePrintWriter extends PrintWriter {
    private PrintWriter[] outs;
    public MutiplePrintWriter(PrintWriter[] outs) { this.out = out; }

    public void print(boolean b) { for (PrintWriter out : outs) print(b); }
    public void print(char c) { for (PrintWriter out : outs) print(c); }
    public void print(char[] s) { for (PrintWriter out : outs) print(s); }
    ...
}

(and the same for Writer, OutputStream...)

Is there a better alternative in Scala?

Is this already implemented in a library in Scala?

gzm0 · Accepted Answer · 2013-06-07 15:25:19Z

1

I can answer your question in the java-world: Implement your multi-writer class on OutputStream level and then stack a Writer/PrintWriter on top:

class MultiOutputStream(val outs: Array[OutputStream]) extends OutputStream {
  override def close() = {
    super.close()
    outs.foreach(_.close)
  }
  override def flush() = {
    super.flush()
    outs.foreach(_.flush)
  }
  def write(c: Int) = outs.foreach(_.write(c))

  // overridden for efficiency
  override def write(b: Array[Byte], off: Int, len: Int) = 
    outs.foreach(_.write(b,off,len))
}

Now create out of this whatever you need:

val outs = //...
val out = new PrintStream(new MultiOutputStream(outs))

This way, the PrintStream takes care of all the formatting business, while you only have to redirect data.

answered Jun 7, 2013 at 15:25

gzm0

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