karaf-2.2.x/shell/log/src/main/java/org/apache/karaf/shell/log/LogTail.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.karaf.shell.log;

import java.io.PrintStream;
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.felix.gogo.commands.Command;
import org.apache.karaf.shell.log.layout.PatternConverter;
import org.apache.karaf.shell.log.layout.PatternParser;
import org.ops4j.pax.logging.spi.PaxAppender;
import org.ops4j.pax.logging.spi.PaxLoggingEvent;

@Command(scope = "log", name = "tail", description = "Continuously display log entries.")
public class LogTail extends DisplayLog {

    protected Object doExecute() throws Exception {
        final PatternConverter cnv = new PatternParser(overridenPattern != null ? overridenPattern : pattern).parse();
        final PrintStream out = System.out;

        Iterable<PaxLoggingEvent> le = events.getElements(entries == 0 ? Integer.MAX_VALUE : entries);
        for (PaxLoggingEvent event : le) {
            display(cnv, event, out);
        }
        // Tail
        final BlockingQueue<PaxLoggingEvent> queue = new LinkedBlockingQueue<PaxLoggingEvent>();
        PaxAppender appender = new PaxAppender() {
            public void doAppend(PaxLoggingEvent event) {
                queue.add(event);
            }
        };
        try {
            events.addAppender(appender);
            for (;;) {
                display(cnv, queue.take(), out);
            }
        } catch (InterruptedException e) {
            // Ignore
        } finally {
            events.removeAppender(appender);
        }
        out.println();
        return null;
    }

}