mail-archive/server/src/main/java/org/apache/sling/mailarchiveserver/util/SysStreamsLogger.java

package org.apache.sling.mailarchiveserver.util;

/**
 * Util class to log System.err and System.out streams.
 * 
 * taken from http://stackoverflow.com/questions/11187461/redirect-system-out-and-system-err-to-slf4j
 * @author itshorty
 */

import java.io.IOException;
import java.io.PrintStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class SysStreamsLogger {
	private static Logger sysOutLogger = LoggerFactory.getLogger("SYSOUT");
	private static Logger sysErrLogger = LoggerFactory.getLogger("SYSERR");

	public static final PrintStream sysout = System.out;
	public static final PrintStream syserr = System.err;

	protected static final String LINE_SEPERATOR = System.getProperty("line.separator");

	public static void bindSystemStreams() {
		// Enable autoflush
		System.setOut(new PrintStream(new LoggingOutputStream(sysOutLogger, false), true));
		System.setErr(new PrintStream(new LoggingOutputStream(sysErrLogger, true), true));
	}

	public static void unbindSystemStreams() {
		System.setOut(sysout);
		System.setErr(syserr);
	}

	private static class LoggingOutputStream extends java.io.OutputStream {

		protected Logger log;
		protected boolean isError;

		/**
		 * Used to maintain the contract of {@link #close()}.
		 */
		protected boolean hasBeenClosed = false;

		/**
		 * The internal buffer where data is stored.
		 */
		protected byte[] buf;

		/**
		 * The number of valid bytes in the buffer. This value is always in the
		 * range <tt>0</tt> through <tt>buf.length</tt>; elements
		 * <tt>buf[0]</tt> through <tt>buf[count-1]</tt> contain valid byte
		 * data.
		 */
		protected int count;

		/**
		 * Remembers the size of the buffer for speed.
		 */
		private int bufLength;

		/**
		 * The default number of bytes in the buffer. =2048
		 */
		public static final int DEFAULT_BUFFER_LENGTH = 2048;

		private LoggingOutputStream() {
			// illegal
		}

		/**
		 * Creates the LoggingOutputStream to flush to the given Category.
		 * 
		 * @param log
		 *            the Logger to write to
		 * 
		 * @param isError
		 *            the if true write to error, else info
		 * 
		 * @exception IllegalArgumentException
		 *                if cat == null or priority == null
		 */
		public LoggingOutputStream(Logger log, boolean isError) throws IllegalArgumentException {
			if (log == null) {
				throw new IllegalArgumentException("log == null");
			}

			this.isError = isError;
			this.log = log;
			bufLength = DEFAULT_BUFFER_LENGTH;
			buf = new byte[DEFAULT_BUFFER_LENGTH];
			count = 0;
		}

		/**
		 * Closes this output stream and releases any system resources
		 * associated with this stream. The general contract of
		 * <code>close</code> is that it closes the output stream. A closed
		 * stream cannot perform output operations and cannot be reopened.
		 */
		@Override
		public void close() {
			flush();
			hasBeenClosed = true;
		}

		/**
		 * Writes the specified byte to this output stream. The general contract
		 * for <code>write</code> is that one byte is written to the output
		 * stream. The byte to be written is the eight low-order bits of the
		 * argument <code>b</code>. The 24 high-order bits of <code>b</code> are
		 * ignored.
		 * 
		 * @param b
		 *            the <code>byte</code> to write
		 */
		@Override
		public void write(final int b) throws IOException {
			if (hasBeenClosed) {
				throw new IOException("The stream has been closed.");
			}

			// don't log nulls
			if (b == 0) {
				return;
			}

			// would this be writing past the buffer?
			if (count == bufLength) {
				// grow the buffer
				final int newBufLength = bufLength + DEFAULT_BUFFER_LENGTH;
				final byte[] newBuf = new byte[newBufLength];

				System.arraycopy(buf, 0, newBuf, 0, bufLength);

				buf = newBuf;
				bufLength = newBufLength;
			}

			buf[count] = (byte) b;
			count++;
		}

		/**
		 * Flushes this output stream and forces any buffered output bytes to be
		 * written out. The general contract of <code>flush</code> is that
		 * calling it is an indication that, if any bytes previously written
		 * have been buffered by the implementation of the output stream, such
		 * bytes should immediately be written to their intended destination.
		 */
		@Override
		public void flush() {

			if (count == 0) {
				return;
			}

			// don't print out blank lines; flushing from PrintStream puts out
			// these
			if (count == LINE_SEPERATOR.length()) {
				if (((char) buf[0]) == LINE_SEPERATOR.charAt(0) && ((count == 1) || // <-
						// Unix
						// &
						// Mac,
						// ->
						// Windows
						((count == 2) && ((char) buf[1]) == LINE_SEPERATOR.charAt(1)))) {
					reset();
					return;
				}
			}

			final byte[] theBytes = new byte[count];

			System.arraycopy(buf, 0, theBytes, 0, count);

			if (isError) {
				log.error(new String(theBytes));
			} else {
				log.info(new String(theBytes));
			}

			reset();
		}

		private void reset() {
			// not resetting the buffer -- assuming that if it grew that it
			// will likely grow similarly again
			count = 0;
		}
	}
}