From 99dc7914b2e83968f95f7b2d37aff6268e0c0bde Mon Sep 17 00:00:00 2001
From: Phillip Webb <pwebb@vmware.com>
Date: Thu, 17 Sep 2020 01:41:39 -0700
Subject: [PATCH] Attempt to fix ConcurrentModificationException

Attempt to fix `ConcurrentModificationException` which occurs on
Java 11+.

See gh-23326
---
 .../org/springframework/boot/DefaultBootstrapContext.java  | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultBootstrapContext.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultBootstrapContext.java
index 9806d34916..79495c0c95 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultBootstrapContext.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/DefaultBootstrapContext.java
@@ -88,7 +88,12 @@ public class DefaultBootstrapContext implements ConfigurableBootstrapContext {
 		synchronized (this.instanceSuppliers) {
 			InstanceSupplier<?> instanceSupplier = this.instanceSuppliers.get(type);
 			Assert.state(instanceSupplier != null, () -> type.getName() + " has not been registered");
-			return (T) this.instances.computeIfAbsent(type, (key) -> instanceSupplier.get(this));
+			T instance = (T) this.instances.get(type);
+			if (instance == null) {
+				instance = (T) instanceSupplier.get(this);
+				this.instances.put(type, instance);
+			}
+			return instance;
 		}
 	}