Defensively use setRemoveOnCancelPolicy for JDK 6 compatibility

Issue: SPR-12238
(cherry picked from commit e003d21)

Author: jhoeller

spring-context/src/main/java/org/springframework/scheduling/concurrent/ScheduledExecutorFactoryBean.java

@@ -27,6 +27,7 @@
 import org.springframework.scheduling.support.DelegatingErrorHandlingRunnable;
 import org.springframework.scheduling.support.TaskUtils;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -66,12 +67,17 @@
 public class ScheduledExecutorFactoryBean extends ExecutorConfigurationSupport
 		implements FactoryBean<ScheduledExecutorService> {
 
-	private int poolSize = 1;
+	// ScheduledThreadPoolExecutor.setRemoveOnCancelPolicy(boolean) only available on JDK 7+
+	private static final boolean setRemoveOnCancelPolicyAvailable =
+			ClassUtils.hasMethod(ScheduledThreadPoolExecutor.class, "setRemoveOnCancelPolicy", boolean.class);
+
 
-	private Boolean removeOnCancelPolicy;
+	private int poolSize = 1;
 
 	private ScheduledExecutorTask[] scheduledExecutorTasks;
 
+	private boolean removeOnCancelPolicy = false;
+
 	private boolean continueScheduledExecutionAfterException = false;
 
 	private boolean exposeUnconfigurableExecutor = false;
@@ -88,14 +94,6 @@ public void setPoolSize(int poolSize) {
 		this.poolSize = poolSize;
 	}
 
-	/**
-	 * Set the same property on ScheduledExecutorService (JDK 1.7+).
-	 * There is no default. If not set, the executor property is not set.
-	 */
-	public void setRemoveOnCancelPolicy(boolean removeOnCancelPolicy) {
-		this.removeOnCancelPolicy = removeOnCancelPolicy;
-	}
-
 	/**
 	 * Register a list of ScheduledExecutorTask objects with the ScheduledExecutorService
 	 * that this FactoryBean creates. Depending on each ScheduledExecutorTask's settings,
@@ -108,6 +106,15 @@ public void setScheduledExecutorTasks(ScheduledExecutorTask... scheduledExecutor
 		this.scheduledExecutorTasks = scheduledExecutorTasks;
 	}
 
+	/**
+	 * Set the remove-on-cancel mode on {@link ScheduledThreadPoolExecutor} (JDK 7+).
+	 * <p>Default is {@code false}. If set to {@code true}, the target executor will be
+	 * switched into remove-on-cancel mode (if possible, with a soft fallback otherwise).
+	 */
+	public void setRemoveOnCancelPolicy(boolean removeOnCancelPolicy) {
+		this.removeOnCancelPolicy = removeOnCancelPolicy;
+	}
+
 	/**
 	 * Specify whether to continue the execution of a scheduled task
 	 * after it threw an exception.
@@ -141,8 +148,13 @@ protected ExecutorService initializeExecutor(
 		ScheduledExecutorService executor =
 				createExecutor(this.poolSize, threadFactory, rejectedExecutionHandler);
 
-		if (executor instanceof ScheduledThreadPoolExecutor && this.removeOnCancelPolicy != null) {
-			((ScheduledThreadPoolExecutor) executor).setRemoveOnCancelPolicy(this.removeOnCancelPolicy);
+		if (this.removeOnCancelPolicy) {
+			if (setRemoveOnCancelPolicyAvailable && executor instanceof ScheduledThreadPoolExecutor) {
+				((ScheduledThreadPoolExecutor) executor).setRemoveOnCancelPolicy(true);
+			}
+			else {
+				logger.info("Could not apply remove-on-cancel policy - not a Java 7+ ScheduledThreadPoolExecutor");
+			}
 		}
 
 		// Register specified ScheduledExecutorTasks, if necessary.

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskScheduler.java

@@ -36,6 +36,7 @@
 import org.springframework.scheduling.Trigger;
 import org.springframework.scheduling.support.TaskUtils;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ErrorHandler;
 import org.springframework.util.concurrent.ListenableFuture;
 import org.springframework.util.concurrent.ListenableFutureTask;
@@ -56,9 +57,14 @@
 public class ThreadPoolTaskScheduler extends ExecutorConfigurationSupport
 		implements AsyncListenableTaskExecutor, SchedulingTaskExecutor, TaskScheduler {
 
+	// ScheduledThreadPoolExecutor.setRemoveOnCancelPolicy(boolean) only available on JDK 7+
+	private static final boolean setRemoveOnCancelPolicyAvailable =
+			ClassUtils.hasMethod(ScheduledThreadPoolExecutor.class, "setRemoveOnCancelPolicy", boolean.class);
+
+
 	private volatile int poolSize = 1;
 
-	private volatile Boolean removeOnCancelPolicy;
+	private volatile boolean removeOnCancelPolicy = false;
 
 	private volatile ScheduledExecutorService scheduledExecutor;
 
@@ -79,33 +85,42 @@ public void setPoolSize(int poolSize) {
 	}
 
 	/**
-	 * Set the same property on ScheduledExecutorService (JDK 1.7+).
-	 * There is no default. If not set, the executor property is not set.
+	 * Set the remove-on-cancel mode on {@link ScheduledThreadPoolExecutor} (JDK 7+).
+	 * <p>Default is {@code false}. If set to {@code true}, the target executor will be
+	 * switched into remove-on-cancel mode (if possible, with a soft fallback otherwise).
 	 * <p><b>This setting can be modified at runtime, for example through JMX.</b>
 	 */
 	public void setRemoveOnCancelPolicy(boolean removeOnCancelPolicy) {
 		this.removeOnCancelPolicy = removeOnCancelPolicy;
-		if (this.scheduledExecutor instanceof ScheduledThreadPoolExecutor) {
+		if (setRemoveOnCancelPolicyAvailable && this.scheduledExecutor instanceof ScheduledThreadPoolExecutor) {
 			((ScheduledThreadPoolExecutor) this.scheduledExecutor).setRemoveOnCancelPolicy(removeOnCancelPolicy);
 		}
+		else if (removeOnCancelPolicy && this.scheduledExecutor != null) {
+			logger.info("Could not apply remove-on-cancel policy - not a Java 7+ ScheduledThreadPoolExecutor");
+		}
 	}
 
 	/**
 	 * Set a custom {@link ErrorHandler} strategy.
 	 */
 	public void setErrorHandler(ErrorHandler errorHandler) {
-		Assert.notNull(errorHandler, "'errorHandler' must not be null");
 		this.errorHandler = errorHandler;
 	}
 
+
 	@Override
 	protected ExecutorService initializeExecutor(
 			ThreadFactory threadFactory, RejectedExecutionHandler rejectedExecutionHandler) {
 
 		this.scheduledExecutor = createExecutor(this.poolSize, threadFactory, rejectedExecutionHandler);
 
-		if (this.scheduledExecutor instanceof ScheduledThreadPoolExecutor && this.removeOnCancelPolicy != null) {
-			((ScheduledThreadPoolExecutor) this.scheduledExecutor).setRemoveOnCancelPolicy(this.removeOnCancelPolicy);
+		if (this.removeOnCancelPolicy) {
+			if (setRemoveOnCancelPolicyAvailable && this.scheduledExecutor instanceof ScheduledThreadPoolExecutor) {
+				((ScheduledThreadPoolExecutor) this.scheduledExecutor).setRemoveOnCancelPolicy(true);
+			}
+			else {
+				logger.info("Could not apply remove-on-cancel policy - not a Java 7+ ScheduledThreadPoolExecutor");
+			}
 		}
 
 		return this.scheduledExecutor;
@@ -166,14 +181,17 @@ public int getPoolSize() {
 	}
 
 	/**
-	 * Return the current setting of removeOnCancelPolicy.
-	 * <p>Requires an underlying {@link ScheduledThreadPoolExecutor} and JDK 1.7+.
+	 * Return the current setting for the remove-on-cancel mode.
+	 * <p>Requires an underlying {@link ScheduledThreadPoolExecutor}.
 	 */
 	public boolean isRemoveOnCancelPolicy() {
-		if (this.scheduledExecutor == null) {
-			// Not initialized yet: return false (the default of the executor)
+		if (!setRemoveOnCancelPolicyAvailable) {
 			return false;
 		}
+		if (this.scheduledExecutor == null) {
+			// Not initialized yet: return our setting for the time being.
+			return this.removeOnCancelPolicy;
+		}
 		return getScheduledThreadPoolExecutor().getRemoveOnCancelPolicy();
 	}