Polish contribution

This commit:

- fixes Checkstyle violations
- improves Javadoc
- adds missing @SInCE tags
- renames getCurrentQueueSize() to getQueueSize()
- avoids NullPointerExceptions in getQueueSize()
- introduces tests for queue size and queue capacity

Closes gh-28583

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

@@ -72,6 +72,8 @@
  * {@link org.springframework.scheduling.concurrent.ConcurrentTaskExecutor} adapter.
  *
  * @author Juergen Hoeller
+ * @author Rémy Guihard
+ * @author Sam Brannen
  * @since 2.0
  * @see org.springframework.core.task.TaskExecutor
  * @see java.util.concurrent.ThreadPoolExecutor
@@ -155,7 +157,7 @@ public int getMaxPoolSize() {
 
 	/**
 	 * Set the ThreadPoolExecutor's keep-alive seconds.
-	 * Default is 60.
+	 * <p>Default is 60.
 	 * <p><b>This setting can be modified at runtime, for example through JMX.</b>
 	 */
 	public void setKeepAliveSeconds(int keepAliveSeconds) {
@@ -178,7 +180,7 @@ public int getKeepAliveSeconds() {
 
 	/**
 	 * Set the capacity for the ThreadPoolExecutor's BlockingQueue.
-	 * Default is {@code Integer.MAX_VALUE}.
+	 * <p>Default is {@code Integer.MAX_VALUE}.
 	 * <p>Any positive value will lead to a LinkedBlockingQueue instance;
 	 * any other value will lead to a SynchronousQueue instance.
 	 * @see java.util.concurrent.LinkedBlockingQueue
@@ -188,6 +190,15 @@ public void setQueueCapacity(int queueCapacity) {
 		this.queueCapacity = queueCapacity;
 	}
 
+	/**
+	 * Return the capacity for the ThreadPoolExecutor's BlockingQueue.
+	 * @since 5.3.21
+	 * @see #setQueueCapacity(int)
+	 */
+	public int getQueueCapacity() {
+		return this.queueCapacity;
+	}
+
 	/**
 	 * Specify whether to allow core threads to time out. This enables dynamic
 	 * growing and shrinking even in combination with a non-zero queue (since
@@ -315,19 +326,18 @@ public int getPoolSize() {
 		}
 		return this.threadPoolExecutor.getPoolSize();
 	}
-
-	/**
-	 * Return the current number of threads waiting in the queue
-	 */
-	public int getCurrentQueueSize() {
-		return this.getThreadPoolExecutor().getQueue().size();
-	}
 
 	/**
-	* Return the maximum capacity of the queue
-	*/
-	public int getQueueCapacity() {
-		return this.queueCapacity;
+	 * Return the current queue size.
+	 * @since 5.3.21
+	 * @see java.util.concurrent.ThreadPoolExecutor#getQueue()
+	 */
+	public int getQueueSize() {
+		if (this.threadPoolExecutor == null) {
+			// Not initialized yet: assume no queued tasks.
+			return 0;
+		}
+		return this.threadPoolExecutor.getQueue().size();
 	}
 
 	/**

spring-context/src/test/java/org/springframework/scheduling/concurrent/ThreadPoolTaskExecutorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -16,17 +16,25 @@
 
 package org.springframework.scheduling.concurrent;
 
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.TimeUnit;
 
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.task.AsyncListenableTaskExecutor;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.InstanceOfAssertFactories.type;
 
 /**
+ * Unit tests for {@link ThreadPoolTaskExecutor}.
+ *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 5.0.5
  */
 class ThreadPoolTaskExecutorTests extends AbstractSchedulingTaskExecutorTests {
@@ -50,8 +58,8 @@ void modifyCorePoolSizeWhileRunning() {
 
 		executor.setCorePoolSize(0);
 
-		assertThat(executor.getCorePoolSize()).isEqualTo(0);
-		assertThat(executor.getThreadPoolExecutor().getCorePoolSize()).isEqualTo(0);
+		assertThat(executor.getCorePoolSize()).isZero();
+		assertThat(executor.getThreadPoolExecutor().getCorePoolSize()).isZero();
 	}
 
 	@Test
@@ -112,4 +120,37 @@ void modifyKeepAliveSecondsWithInvalidValueWhileRunning() {
 		assertThat(executor.getThreadPoolExecutor().getKeepAliveTime(TimeUnit.SECONDS)).isEqualTo(60);
 	}
 
+	@Test
+	void queueCapacityDefault() {
+		assertThat(executor.getQueueCapacity()).isEqualTo(Integer.MAX_VALUE);
+		assertThat(executor.getThreadPoolExecutor().getQueue())
+			.asInstanceOf(type(LinkedBlockingQueue.class))
+			.extracting(BlockingQueue::remainingCapacity).isEqualTo(Integer.MAX_VALUE);
+	}
+
+	@Test
+	void queueCapacityZero() {
+		executor.setQueueCapacity(0);
+		executor.afterPropertiesSet();
+
+		assertThat(executor.getQueueCapacity()).isZero();
+		assertThat(executor.getThreadPoolExecutor().getQueue())
+			.asInstanceOf(type(SynchronousQueue.class))
+			.extracting(BlockingQueue::remainingCapacity).isEqualTo(0);
+	}
+
+	@Test
+	void queueSize() {
+		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+
+		assertThatIllegalStateException().isThrownBy(executor::getThreadPoolExecutor);
+		assertThat(executor.getQueueSize()).isZero();
+
+		executor.afterPropertiesSet();
+
+		assertThat(executor.getThreadPoolExecutor()).isNotNull();
+		assertThat(executor.getThreadPoolExecutor().getQueue()).isEmpty();
+		assertThat(executor.getQueueSize()).isZero();
+	}
+
 }