src/main/java/org/apache/sling/startupfilter/impl/StartupFilterImpl.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.sling.startupfilter.impl;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Service;
import org.apache.sling.startupfilter.StartupFilter;
import org.apache.sling.startupfilter.StartupInfoProvider;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.framework.ServiceRegistration;
import org.osgi.service.component.ComponentContext;
import org.osgi.util.tracker.ServiceTracker;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/** StartupFilter implementation. Initially registered
 *  as a StartupFilter only, the Filter registration
 *  is dynamic, on-demand. */
@Component(immediate=true, metatype=true)
@Service(value=StartupFilter.class)
public class StartupFilterImpl implements StartupFilter, Filter {

    private final Logger log = LoggerFactory.getLogger(getClass());
    private ServiceRegistration filterServiceRegistration;
    private BundleContext bundleContext;
    private ServiceTracker providersTracker;
    private int providersTrackerCount = -1;
    
    private final List<StartupInfoProvider> providers = new ArrayList<StartupInfoProvider>();
    
    @Property(boolValue=true)
    public static final String ACTIVE_BY_DEFAULT_PROP = "active.by.default";
    private boolean defaultFilterActive;
    
    public static final String DEFAULT_MESSAGE = "Startup in progress";
    
    @Property(value=DEFAULT_MESSAGE)
    public static final String DEFAULT_MESSAGE_PROP = "default.message";
    private String defaultMessage;
    
    /** @inheritDoc */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        updateProviders();
        
        final StringBuilder sb = new StringBuilder();
        sb.append(defaultMessage);
        for(StartupInfoProvider p : providers) {
            sb.append('\n');
            sb.append(p.getProgressInfo());
        }
        ((HttpServletResponse)response).sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sb.toString());
    }

    /** @inheritDoc */
    public void destroy() {
    }

    /** @inheritDoc */
    public void init(FilterConfig cfg) throws ServletException {
    }
    
    /** If needed, update our list of providers */
    private void updateProviders() {
        if(providersTracker.getTrackingCount() != providersTrackerCount) {
            synchronized(this) {
                if(providersTracker.getTrackingCount() != providersTrackerCount) {
                    providers.clear();
                    final ServiceReference [] refs = providersTracker.getServiceReferences();
                    if(refs != null) {
                        for(ServiceReference ref : refs) {
                            providers.add((StartupInfoProvider)bundleContext.getService(ref));
                        }
                    }
                }
                providersTrackerCount = providersTracker.getTrackingCount();
                log.info("Reloaded list of StartupInfoProvider: {}", providers);
            }
        }
    }

    @Activate
    protected void activate(ComponentContext ctx) throws InterruptedException {
        bundleContext = ctx.getBundleContext();
        
        providersTracker = new ServiceTracker(bundleContext, StartupInfoProvider.class.getName(), null);
        providersTracker.open();
        
        Object prop = ctx.getProperties().get(DEFAULT_MESSAGE_PROP);
        defaultMessage = prop == null ? DEFAULT_MESSAGE : prop.toString();
                
        prop = ctx.getProperties().get(ACTIVE_BY_DEFAULT_PROP);
        defaultFilterActive = (prop instanceof Boolean ? (Boolean)prop : false);
        if(defaultFilterActive) {
            enable();
        }
        log.info("Activated, enabled={}", isEnabled());
    }
    
    @Deactivate
    protected void deactivate(ComponentContext ctx) throws InterruptedException {
        disable();
        providersTracker.close();
        providersTracker = null;
        bundleContext = null;
    }
    
    
    public synchronized void enable() {
        if(filterServiceRegistration == null) {
            final Hashtable<String, String> params = new Hashtable<String, String>();
            params.put("filter.scope", "REQUEST");
            filterServiceRegistration = bundleContext.registerService(Filter.class.getName(), this, params);
            log.info("Registered {} as a Filter service", this);
        }
    }
    
    public synchronized void disable() {
        if(filterServiceRegistration != null) {
            filterServiceRegistration.unregister();
            filterServiceRegistration = null;
            log.info("Filter service disabled");
        }
    }
    
    public synchronized boolean isEnabled() {
        return filterServiceRegistration != null;
    }
}