diff --git a/spring-aop/src/test/java/org/springframework/aop/interceptor/CustomizableTraceInterceptorTests.java b/spring-aop/src/test/java/org/springframework/aop/interceptor/CustomizableTraceInterceptorTests.java
index b98acc38e94d..ebf44f27fcdd 100644
--- a/spring-aop/src/test/java/org/springframework/aop/interceptor/CustomizableTraceInterceptorTests.java
+++ b/spring-aop/src/test/java/org/springframework/aop/interceptor/CustomizableTraceInterceptorTests.java
@@ -143,13 +143,13 @@ public void testSunnyDayPathLogsCorrectlyWithPrettyMuchAllPlaceholdersMatching()
 		given(log.isTraceEnabled()).willReturn(true);
 
 		CustomizableTraceInterceptor interceptor = new StubCustomizableTraceInterceptor(log);
-		interceptor.setEnterMessage(new StringBuffer()
+		interceptor.setEnterMessage(new StringBuilder()
 			.append("Entering the '").append(CustomizableTraceInterceptor.PLACEHOLDER_METHOD_NAME)
 			.append("' method of the [").append(CustomizableTraceInterceptor.PLACEHOLDER_TARGET_CLASS_NAME)
 			.append("] class with the following args (").append(CustomizableTraceInterceptor.PLACEHOLDER_ARGUMENTS)
 			.append(") and arg types (").append(CustomizableTraceInterceptor.PLACEHOLDER_ARGUMENT_TYPES)
 			.append(").").toString());
-		interceptor.setExitMessage(new StringBuffer()
+		interceptor.setExitMessage(new StringBuilder()
 			.append("Exiting the '").append(CustomizableTraceInterceptor.PLACEHOLDER_METHOD_NAME)
 			.append("' method of the [").append(CustomizableTraceInterceptor.PLACEHOLDER_TARGET_CLASS_SHORT_NAME)
 			.append("] class with the following args (").append(CustomizableTraceInterceptor.PLACEHOLDER_ARGUMENTS)
diff --git a/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTestTypes.java b/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTestTypes.java
index 0d846d9d1243..01c0f5413df3 100644
--- a/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTestTypes.java
+++ b/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTestTypes.java
@@ -589,7 +589,7 @@ class ReverseMethodReplacer implements MethodReplacer, Serializable {
 	@Override
 	public Object reimplement(Object obj, Method method, Object[] args) throws Throwable {
 		String s = (String) args[0];
-		return new StringBuffer(s).reverse().toString();
+		return new StringBuilder(s).reverse().toString();
 	}
 }
 
diff --git a/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTests.java b/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTests.java
index edf72fdcf2b3..a1e3f81940aa 100644
--- a/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTests.java
+++ b/spring-context/src/test/java/org/springframework/beans/factory/xml/XmlBeanFactoryTests.java
@@ -1324,7 +1324,7 @@ void replaceMethodOverrideWithSetterInjection() {
 
 		// Now test replace
 		String s = "this is not a palindrome";
-		String reverse = new StringBuffer(s).reverse().toString();
+		String reverse = new StringBuilder(s).reverse().toString();
 		assertThat(oom.replaceMe(s)).as("Should have overridden to reverse, not echo").isEqualTo(reverse);
 
 		assertThat(oom.replaceMe()).as("Should have overridden no-arg overloaded replaceMe method to return fixed value").isEqualTo(FixedMethodReplacer.VALUE);
@@ -1380,7 +1380,7 @@ void serializableMethodReplacerAndSuperclass() throws IOException {
 		reader.loadBeanDefinitions(DELEGATION_OVERRIDES_CONTEXT);
 		SerializableMethodReplacerCandidate s = (SerializableMethodReplacerCandidate) xbf.getBean("serializableReplacer");
 		String forwards = "this is forwards";
-		String backwards = new StringBuffer(forwards).reverse().toString();
+		String backwards = new StringBuilder(forwards).reverse().toString();
 		assertThat(s.replaceMe(forwards)).isEqualTo(backwards);
 		// SPR-356: lookup methods & method replacers are not serializable.
 		assertThat(SerializationTestUtils.isSerializable(s)).as("Lookup methods and method replacers are not meant to be serializable.").isFalse();
diff --git a/spring-context/src/test/java/org/springframework/scripting/MessengerScrambler.java b/spring-context/src/test/java/org/springframework/scripting/MessengerScrambler.java
index fba76773e167..36320d0c1597 100644
--- a/spring-context/src/test/java/org/springframework/scripting/MessengerScrambler.java
+++ b/spring-context/src/test/java/org/springframework/scripting/MessengerScrambler.java
@@ -28,7 +28,7 @@ public class MessengerScrambler {
 
 	public String scramble(ProceedingJoinPoint pjp) throws Throwable {
 		String message = (String) pjp.proceed();
-		return new StringBuffer(message).reverse().toString();
+		return new StringBuilder(message).reverse().toString();
 	}
 
 }
diff --git a/spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java b/spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java
index 1af56bd8366f..a8f4cb5da7d7 100644
--- a/spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java
+++ b/spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java
@@ -260,7 +260,7 @@ private static Class getClass(String className, ClassLoader loader, String[] pac
 		while ((index = className.indexOf("[]", index) + 1) > 0) {
 			dimensions++;
 		}
-		StringBuffer brackets = new StringBuffer(className.length() - dimensions);
+		StringBuilder brackets = new StringBuilder(className.length() - dimensions);
 		for (int i = 0; i < dimensions; i++) {
 			brackets.append('[');
 		}