added PeriodicTrigger implementation

org.springframework.context/src/main/java/org/springframework/scheduling/support/PeriodicTrigger.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright 2002-2009 the original author or authors.
+ *
+ * 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.springframework.scheduling.support;
+
+import java.util.Date;
+import java.util.concurrent.TimeUnit;
+
+import org.springframework.scheduling.Trigger;
+import org.springframework.scheduling.TriggerContext;
+import org.springframework.util.Assert;
+
+/**
+ * A trigger for periodic task execution. The period may be applied as either
+ * fixed-rate or fixed-delay, and an initial delay value may also be configured.
+ * The default initial delay is 0, and the default behavior is fixed-delay
+ * (i.e. the interval between successive executions is measured from each
+ * <emphasis>completion</emphasis> time). To measure the interval between the
+ * scheduled <emphasis>start</emphasis> time of each execution instead, set the
+ * 'fixedRate' property to <code>true</code>.
+ * <p>
+ * Note that the TaskScheduler interface already defines methods for scheduling
+ * tasks at fixed-rate or with fixed-delay. Both also support an optional value
+ * for the initial delay. Those methods should be used directly whenever
+ * possible. The value of this Trigger implementation is that it can be used
+ * within components that rely on the Trigger abstraction. For example, it may
+ * be convenient to allow periodic triggers, cron-based triggers, and even
+ * custom Trigger implementations to be used interchangeably.
+ * 
+ * @author Mark Fisher
+ * @since 3.0
+ */
+public class PeriodicTrigger implements Trigger {
+
+	private final long period;
+
+	private final TimeUnit timeUnit;
+
+	private volatile long initialDelay = 0;
+
+	private volatile boolean fixedRate = false;
+
+
+	/**
+	 * Create a trigger with the given period in milliseconds.
+	 */
+	public PeriodicTrigger(long period) {
+		this(period, null);
+	}
+
+	/**
+	 * Create a trigger with the given period and time unit. The time unit will
+	 * apply not only to the period but also to any 'initialDelay' value, if
+	 * configured on this Trigger later via {@link #setInitialDelay(long)}.
+	 */
+	public PeriodicTrigger(long period, TimeUnit timeUnit) {
+		Assert.isTrue(period >= 0, "period must not be negative");
+		this.timeUnit = (timeUnit != null) ? timeUnit : TimeUnit.MILLISECONDS;
+		this.period = this.timeUnit.toMillis(period);
+	}
+
+
+	/**
+	 * Specify the delay for the initial execution. It will be evaluated in
+	 * terms of this trigger's {@link TimeUnit}. If no time unit was explicitly
+	 * provided upon instantiation, the default is milliseconds. 
+	 */
+	public void setInitialDelay(long initialDelay) {
+		this.initialDelay = this.timeUnit.toMillis(initialDelay);
+	}
+
+	/**
+	 * Specify whether the periodic interval should be measured between the
+	 * scheduled start times rather than between actual completion times.
+	 * The latter, "fixed delay" behavior, is the default.
+	 */
+	public void setFixedRate(boolean fixedRate) {
+		this.fixedRate = fixedRate;
+	}
+
+	/**
+	 * Returns the time after which a task should run again.
+	 */
+	public Date nextExecutionTime(TriggerContext triggerContext) {
+		if (triggerContext.lastScheduledExecutionTime() == null) {
+			return new Date(System.currentTimeMillis() + this.initialDelay);
+		}
+		else if (this.fixedRate) {
+			return new Date(triggerContext.lastScheduledExecutionTime().getTime() + this.period);
+		}
+		return new Date(triggerContext.lastCompletionTime().getTime() + this.period);
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) {
+			return true;
+		}
+		if (!(obj instanceof PeriodicTrigger)) {
+			return false;
+		}
+		PeriodicTrigger other = (PeriodicTrigger) obj;
+		return this.fixedRate == other.fixedRate
+				&& this.initialDelay == other.initialDelay
+				&& this.period == other.period;
+	}
+
+	@Override
+	public int hashCode() {
+		return (this.fixedRate ? 17 : 29) +
+				(int) (37 * this.period) +
+				(int) (41 * this.initialDelay); 
+	}
+
+}