src/main/java/org/apache/log4j/ConsoleAppender.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j;

import java.io.IOException;
import java.io.OutputStream;
import org.apache.log4j.helpers.LogLog;

/**
  * ConsoleAppender appends log events to <code>System.out</code> or
  * <code>System.err</code> using a layout specified by the user. The
  * default target is <code>System.out</code>.
  *
  * @author Ceki G&uuml;lc&uuml; 
  * @author Curt Arnold
  * @since 1.1 */
public class ConsoleAppender extends WriterAppender {

  public static final String SYSTEM_OUT = "System.out";
  public static final String SYSTEM_ERR = "System.err";

  protected String target = SYSTEM_OUT;

  /**
   *  Determines if the appender honors reassignments of System.out
   *  or System.err made after configuration.
   */
  private boolean follow = false;

  /**
    * Constructs an unconfigured appender.
    */
  public ConsoleAppender() {
  }

    /**
     * Creates a configured appender.
     *
     * @param layout layout, may not be null.
     */
  public ConsoleAppender(Layout layout) {
    this(layout, SYSTEM_OUT);
  }

    /**
     *   Creates a configured appender.
     * @param layout layout, may not be null.
     * @param target target, either "System.err" or "System.out".
     */
  public ConsoleAppender(Layout layout, String target) {
    setLayout(layout);
    setTarget(target);
    activateOptions();
  }

  /**
   *  Sets the value of the <b>Target</b> option. Recognized values
   *  are "System.out" and "System.err". Any other value will be
   *  ignored.  
   * */
  public
  void setTarget(String value) {
    String v = value.trim();

    if (SYSTEM_OUT.equalsIgnoreCase(v)) {
      target = SYSTEM_OUT;
    } else if (SYSTEM_ERR.equalsIgnoreCase(v)) {
      target = SYSTEM_ERR;
    } else {
      targetWarn(value);
    }
  }

  /**
   * Returns the current value of the <b>Target</b> property. The
   * default value of the option is "System.out".
   *
   * See also {@link #setTarget}.
   * */
  public
  String getTarget() {
    return target;
  }
  
  /**
   *  Sets whether the appender honors reassignments of System.out
   *  or System.err made after configuration.
   *  @param newValue if true, appender will use value of System.out or
   *  System.err in force at the time when logging events are appended.
   *  @since 1.2.13
   */
  public final void setFollow(final boolean newValue) {
     follow = newValue;
  }
  
  /**
   *  Gets whether the appender honors reassignments of System.out
   *  or System.err made after configuration.
   *  @return true if appender will use value of System.out or
   *  System.err in force at the time when logging events are appended.
   *  @since 1.2.13
   */
  public final boolean getFollow() {
      return follow;
  }

  void targetWarn(String val) {
    LogLog.warn("["+val+"] should be System.out or System.err.");
    LogLog.warn("Using previously set target, System.out by default.");
  }

  /**
    *   Prepares the appender for use.
    */
   public void activateOptions() {
        if (follow) {
            if (target.equals(SYSTEM_ERR)) {
               setWriter(createWriter(new SystemErrStream()));
            } else {
               setWriter(createWriter(new SystemOutStream()));
            }
        } else {
            if (target.equals(SYSTEM_ERR)) {
               setWriter(createWriter(System.err));
            } else {
               setWriter(createWriter(System.out));
            }
        }

        super.activateOptions();
  }
  
  /**
   *  {@inheritDoc}
   */
  protected
  final
  void closeWriter() {
     if (follow) {
        super.closeWriter();
     }
  }
  

    /**
     * An implementation of OutputStream that redirects to the
     * current System.err.
     *
     */
    private static class SystemErrStream extends OutputStream {
        public SystemErrStream() {
        }

        public void close() {
        }

        public void flush() {
            System.err.flush();
        }

        public void write(final byte[] b) throws IOException {
            System.err.write(b);
        }

        public void write(final byte[] b, final int off, final int len)
            throws IOException {
            System.err.write(b, off, len);
        }

        public void write(final int b) throws IOException {
            System.err.write(b);
        }
    }

    /**
     * An implementation of OutputStream that redirects to the
     * current System.out.
     *
     */
    private static class SystemOutStream extends OutputStream {
        public SystemOutStream() {
        }

        public void close() {
        }

        public void flush() {
            System.out.flush();
        }

        public void write(final byte[] b) throws IOException {
            System.out.write(b);
        }

        public void write(final byte[] b, final int off, final int len)
            throws IOException {
            System.out.write(b, off, len);
        }

        public void write(final int b) throws IOException {
            System.out.write(b);
        }
    }

}