Quick access to volatile field (full synchronization only for lazy init)

Issue: SPR-16570

spring-aop/src/main/java/org/springframework/aop/target/AbstractBeanFactoryBasedTargetSource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -60,7 +60,7 @@ public abstract class AbstractBeanFactoryBasedTargetSource implements TargetSour
 	private String targetBeanName;
 
 	/** Class of the target */
-	private Class<?> targetClass;
+	private volatile Class<?> targetClass;
 
 	/**
 	 * BeanFactory that owns this TargetSource. We need to hold onto this
@@ -120,19 +120,28 @@ public abstract class AbstractBeanFactoryBasedTargetSource implements TargetSour
 
 
 	@Override
-	public synchronized Class<?> getTargetClass() {
-		if (this.targetClass == null && this.beanFactory != null) {
-			// Determine type of the target bean.
-			this.targetClass = this.beanFactory.getType(this.targetBeanName);
-			if (this.targetClass == null) {
-				if (logger.isTraceEnabled()) {
-					logger.trace("Getting bean with name '" + this.targetBeanName + "' in order to determine type");
+	public Class<?> getTargetClass() {
+		Class<?> targetClass = this.targetClass;
+		if (targetClass != null) {
+			return targetClass;
+		}
+		synchronized (this) {
+			// Full check within synchronization, entering the BeanFactory interaction algorithm only once...
+			targetClass = this.targetClass;
+			if (targetClass == null && this.beanFactory != null) {
+				// Determine type of the target bean.
+				targetClass = this.beanFactory.getType(this.targetBeanName);
+				if (targetClass == null) {
+					if (logger.isTraceEnabled()) {
+						logger.trace("Getting bean with name '" + this.targetBeanName + "' for type determination");
+					}
+					Object beanInstance = this.beanFactory.getBean(this.targetBeanName);
+					targetClass = beanInstance.getClass();
 				}
-				Object beanInstance = this.beanFactory.getBean(this.targetBeanName);
-				this.targetClass = beanInstance.getClass();
+				this.targetClass = targetClass;
 			}
+			return targetClass;
 		}
-		return this.targetClass;
 	}
 
 	@Override

spring-jdbc/src/main/java/org/springframework/jdbc/support/JdbcAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -46,7 +46,7 @@ public abstract class JdbcAccessor implements InitializingBean {
 	private DataSource dataSource;
 
 	@Nullable
-	private SQLExceptionTranslator exceptionTranslator;
+	private volatile SQLExceptionTranslator exceptionTranslator;
 
 	private boolean lazyInit = true;
 
@@ -109,17 +109,25 @@ public abstract class JdbcAccessor implements InitializingBean {
 	 * {@link SQLStateSQLExceptionTranslator} in case of no DataSource.
 	 * @see #getDataSource()
 	 */
-	public synchronized SQLExceptionTranslator getExceptionTranslator() {
-		if (this.exceptionTranslator == null) {
-			DataSource dataSource = getDataSource();
-			if (dataSource != null) {
-				this.exceptionTranslator = new SQLErrorCodeSQLExceptionTranslator(dataSource);
-			}
-			else {
-				this.exceptionTranslator = new SQLStateSQLExceptionTranslator();
+	public SQLExceptionTranslator getExceptionTranslator() {
+		SQLExceptionTranslator exceptionTranslator = this.exceptionTranslator;
+		if (exceptionTranslator != null) {
+			return exceptionTranslator;
+		}
+		synchronized (this) {
+			exceptionTranslator = this.exceptionTranslator;
+			if (exceptionTranslator == null) {
+				DataSource dataSource = getDataSource();
+				if (dataSource != null) {
+					exceptionTranslator = new SQLErrorCodeSQLExceptionTranslator(dataSource);
+				}
+				else {
+					exceptionTranslator = new SQLStateSQLExceptionTranslator();
+				}
+				this.exceptionTranslator = exceptionTranslator;
 			}
+			return exceptionTranslator;
 		}
-		return this.exceptionTranslator;
 	}
 
 	/**