Add output stream that unions other output streams

This will be extremely useful for intercepting stdout and stderr output
without repeatedly calling System.setOut/setErr and battling over who
gets to be "the guy." Everyone can be the guy -- they just have to add
themselves to the MultiOutputStream.

Author: ctrueden

src/main/java/org/scijava/console/MultiOutputStream.java

@@ -0,0 +1,113 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2015 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.console;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.ArrayList;
+
+/**
+ * A {@code MultiOutputStream} is a collection of constituent
+ * {@link OutputStream} objects, to which all output is forwarded.
+ * <p>
+ * Thanks to Ian F. Darwin for <a href=
+ * "http://www.java2s.com/Code/Java/File-Input-Output/TeePrintStreamteesallPrintStreamoperationsintoafileratherliketheUNIXtee1command.htm"
+ * >his implementation of a similar concept</a>.
+ * </p>
+ *
+ * @author Curtis Rueden
+ */
+public class MultiOutputStream extends OutputStream {
+
+	private final ArrayList<OutputStream> streams;
+
+	/**
+	 * Forwards output to a list of output streams.
+	 *
+	 * @param os Output streams which will receive this stream's output.
+	 */
+	public MultiOutputStream(final OutputStream... os) {
+		streams = new ArrayList<OutputStream>(os.length);
+		for (int i = 0; i < os.length; i++) {
+			streams.add(os[i]);
+		}
+	}
+
+	// -- MultiOutputStream methods --
+
+	/** Adds an output stream to those receiving this stream's output. */
+	public void addOutputStream(final OutputStream os) {
+		synchronized (streams) {
+			streams.add(os);
+		}
+	}
+
+	/** Removes an output stream from those receiving this stream's output. */
+	public void removeOutputStream(final OutputStream os) {
+		synchronized (streams) {
+			streams.remove(os);
+		}
+	}
+
+	// -- OutputStream methods --
+
+	@Override
+	public void write(final int b) throws IOException {
+		for (final OutputStream stream : streams)
+			stream.write(b);
+	}
+
+	@Override
+	public void write(final byte[] buf, final int off, final int len)
+		throws IOException
+	{
+		for (final OutputStream stream : streams)
+			stream.write(buf, off, len);
+	}
+
+	// -- Closeable methods --
+
+	@Override
+	public void close() throws IOException {
+		for (final OutputStream stream : streams)
+			stream.close();
+	}
+
+	// -- Flushable methods --
+
+	@Override
+	public void flush() throws IOException {
+		for (final OutputStream stream : streams)
+			stream.flush();
+	}
+
+}