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

/*
 * Copyright 1999,2005 The Apache Software Foundation.
 *
 * Licensed 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;


/**
  * 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 <a href="http://www.qos.ch/log4j/">Ceki G&uuml;lc&uuml;</a>
  * @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(final Layout layout) {
        setLayout(layout);
        activateOptions();
    }

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

        if (SYSTEM_OUT.equalsIgnoreCase(v)) {
            target = SYSTEM_OUT;
        } else if (SYSTEM_ERR.equalsIgnoreCase(v)) {
            target = SYSTEM_ERR;
        } else {
            getLogger().warn("[{}] should be System.out or System.err.", value);
            getLogger().warn("Using previously set target, System.out by default.");
        }
    }

    /**
     * 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;
    }


    /**
     *   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);
        }
    }
}