Improve error reporting when driver class version is unsupported

ClassUtils.isPresent(String, ClassLoader) swallows all Throwables when
trying to load a class by name. For this reason
UnsupportedClassVersionError will also be swallowed when user code is
trying to use a driver library which has been compiled with a later
JDK than the one the application is running with. All the user would

see was "Cannot load driver class". This change simply propagates the
UnsupportedClassVersionNumberError so that it is easier for users to
find the root cause of the problem.

Closes gh-4082
Closes gh-4091

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceProperties.java

@@ -161,7 +161,7 @@ public class DataSourceProperties implements BeanClassLoaderAware, EnvironmentAw
 
 	public String getDriverClassName() {
 		if (StringUtils.hasText(this.driverClassName)) {
-			Assert.state(ClassUtils.isPresent(this.driverClassName, null),
+			Assert.state(driverClassIsLoadable(),
 					"Cannot load driver class: " + this.driverClassName);
 			return this.driverClassName;
 		}
@@ -182,6 +182,20 @@ public class DataSourceProperties implements BeanClassLoaderAware, EnvironmentAw
 		return driverClassName;
 	}
 
+	private boolean driverClassIsLoadable() {
+		try {
+			ClassUtils.forName(this.driverClassName, null);
+			return true;
+		}
+		catch (UnsupportedClassVersionError ucve) {
+			// driver library has been compiled with a later JDK, propagate error
+			throw ucve;
+		}
+		catch (Throwable t) {
+			return false;
+		}
+	}
+
 	public void setDriverClassName(String driverClassName) {
 		this.driverClassName = driverClassName;
 	}