Daemon.java

package act.app;

/*-
 * #%L
 * ACT Framework
 * %%
 * Copyright (C) 2014 - 2017 ActFramework
 * %%
 * 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.
 * #L%
 */

import org.joda.time.DateTime;

import java.util.Map;

/**
 * A daemon encapsulate a long running logic that can be
 *
 * * {@link #start() started}
 * * {@link #stop() stopped}
 * * {@link #restart() restart}
 * * Check {@link #state() state}
 */
public interface Daemon extends Runnable {

    enum State {
        STOPPING, STOPPED, STARTING, STARTED, ERROR, FATAL
    }

    /**
     * Start this daemon
     */
    void start();

    /**
     * Stop this daemon
     */
    void stop();

    /**
     * {@link #stop() stop} this daemon first and then {@link #start() start}
     */
    void restart();

    /**
     * Returns the {@link State state} of this daemon
     * @return the state
     */
    State state();

    /**
     * Returns the timestamp when last state transfer happening
     * @return the timestamp
     */
    DateTime timestamp();

    /**
     * Returns ID of the daemon logic
     * @return ID
     */
    String id();

    /**
     * Returns last error
     * @return the last error encountered
     */
    Exception lastError();

    /**
     * Returns the timestamp when last error happening
     * @return the timestamp
     */
    DateTime errorTimestamp();

    /**
     * Set an attribute to the daemon
     * @param key the attribute key
     * @param value attribute value
     */
    void setAttribute(String key, Object value);

    /**
     * Remove an attribute from a daemon
     * @param key the attribute key
     */
    void removeAttribute(String key);

    /**
     * Return the attribute set to the daemon
     * @param key the attribute key
     * @param <T> the gneric type of the attribute value
     * @return the attribute value
     */
    <T> T getAttribute(String key);

    /**
     * Returns all attributes set on this daemon
     * @return the attributes set on this daemon
     */
    Map<String, Object> getAttributes();
}